Displaying items by tag: porsche

Your Boxster or Cayman is in the best of hands at JMG Porsche, where even with servicing we go beyond the factory schedule.

The factory schedule for many models called for a service every two years, which was fine when the car was new and to make the car last beyond the factory warranty without issue. However we strongly recommend that all models are serviced annually, alternating between a minor and a major service each year. Click here and read our article for more information.

Servicing and repair advice for the the Boxster and Cayman models.


Service interval - We strongly advise that all Porsche cars are serviced every year, with a major service every two years.

The service schedule can be confusing with some service items needing to be performed every X amount of years, with other items being specified every Y amount of miles.

At JMG Porsche we have built a database for each model car, where every two years of age for your car, has listed the major service it requires in that year, which combined with every year in between major services the car having an annual service.

This means that for your model of Porsche, we can provide you with a plain price list for servicing, no matter what year your car was made, which makes it easy to see what service items are due and what the total cost will be.

To get a copy of the current service guide and price list for your Porsche, just email us to have your copy emailed to you in PDF format.

Eventually we plan on making it possible to register to the website and be able to download the latest version of this price list - Watch this space!


Engine failures - Not nearly as common as horror stories on the internet would have you believe, but there are still worthwhile ways of avoiding unexpected large engine rebuild costs. One of which is proper servicing by a real Porsche specialist, which may not need cost as much as you think. There are also some ways to avoid unexpected bills by following some of our other advice bellow.

Brake fluid - Did you realise this should be changed every two years? Not doing this can cause problems with expensive parts within your car, such as the ABS pump or any part of the brake hydraulics due to water contamination as the brake fluid actually sucks moisture out of the air (hydroscopic), so even if the car is not used, the brake fluid must be changed every two years!

Water Pump - Often thought of as a part which fails with age, mileage and quite suddenly, leaving you stranded, our expert technicians are used to inspecting these during services, and so may spot tell tale signs of failure long before they become an issue, so saving you from the indignity of being broken down at the side of the road.

IMS Bearing - The famous intermediate shaft bearing (IMS Bearing) is an important bearing within the engine. These can fail on pre 2005 models of Boxster and cause catestrophic damage to the engine, sometimes costing thousands to repair. However there is a better design of bearing available, which our engine specialists at JMG Porsche have developed some cost effective ways to install and remove the risk of this kind of engine failure. Typically, the most cost effective time to replace this bearing with the better design is at the same time as a clutch replacement. However if you do not need a clutch now, or own a tiptronic Boxster, then we can perform this job at any time.

RMS - Rear main seal - Something else you might see horror stories on the internet about, these used to be a real problem and Porsche re designed the part several times to arrive at the current design which is the only one we at JMG Porsche use. Like an IMS Bearing replacement, this is best performed during a clutch change, however on tiptronic models or on cars not needing a clutch, they can be changed at any time.

Transmission services - Not clearly noted by Porsche for when the transmission should be serviced and this vital expensive part of your car should not be overlooked. Just like your engine, the transmission is filled with oil/transmission fluid, which over time degrades. Not only this, but not many realise that many Porsche transmissions also contain a filter, which becomes clogged over time and can starve your transmission of lubrication, causing expensive repairs. We recommend all Porsche transmissions are serviced every 4 years or 40,000 miles, whichever comes soonest.

Air Oil Separator - If your Porsche is producing some smoke, especially when it starts up in the morning, it could be that the air oil separator has failed rather than your whole engine being damaged. This simple device is designed to allow your engine to pass polution regulations and should not cost the earth to replace, at least much less expensive than rebuilding an engine!

Drive Belt - Many of you may have had cars where a drive belt, timing belt or cam belt needs to be changed at a regular interval. Your Porsche model has a belt which should be changed every 4 years. Failure to do so can cause instant overheating, loss of power steering and damage to the engine very suddenly. We recommend you have this changed at least every 4 years.

Heavy clutch? - A heavy feeling clutch which is stiff to use is not normal on a Porsche and often a sign that the clutch has almost worn out. Ignoring this can cause further damage, such as to the dual mass flywheel and clutch fork.

Alarm system - At JMG Porsche we are experts of all Porsche security systems and have reverse engineered all the various control units. This not only means we can program new alarm control units and keys to your car, just as the main dealer can, but in some cases we can repair your old alarm control unit and keys, or in some cases recover your old keys to be used on the new alarm control unit, which is a service unique to JMG.

Alarm system causes - In most cases the cause of alarm control unit failure is water damage, we can perform modifications to your Porsche model to help mitigate the chances of this happening to your Porsche.


The importance of routine annual servicing.


Everyone knows that a car needs to be serviced to keep it reliable and to avoid expensive repairs.

However there are two occasions where Porsche owners may believe that their car does not need servicing every year.


But the service book says to service the car every two years.”

Many more modern Porsche models specify two yearly servicing in the service book for the car, which is fine for the first four years of the car's life, as the factory are focussed on the car lasting beyond the duration of the factory warranty. Beyond this, you are on your own.. However we will explain later in this article why this can be a big mistake.


But I only cover a few miles per year.”

Because often servicing is specified in the service book as yearly or every other year, but also at a set mileage, many people believe that if they have only covered 200 miles in a year, that the car does not need a service.

However, chemistry within your engine will turn your oil from a protecting fluid, into a toxic chemical soup which can literally eat your engine components alive.


Engine oil over two years old is where chemistry becomes your enemy!

Once you start your engine with fresh engine oil a process begins where the oil will be contaminated with hydrocarbons from the combustion process, even if the engine was only started once, when the engine oil has been mixed with these chemical compounds for a year, the oil will have broken down and the chemicals will have become more toxic to your engine.

The engine oil will have begun life as a relatively neutral compound, neither overly acidic or caustic. However hydrocarbons from combustion, entering the oil past your piston rings will have begun to change all of that, some of these compounds only need moisture to become even more toxic.

You may not realise but when your engine is stopped and cooled, any moisture from humidity in the air will collect and condense within the engine and drain back into the oil, more humid air will enter the engine and this also will condense. This moisture will kick start other chemical reactions within the engine oil and especially reacting with the combustion by products within the no longer fresh engine oil.

When the engine is next started, fresh chemical reactions begin, additives within the oil can be destroyed and the chemical make up of the oil within the engine changes further.


This vicious circle is worse with infrequently used cars, as regular use will cause the moisture to evaporate away and have less time to damage the molecules and composition of the engine oil.

This problem is also made worse the longer the engine oil is within the engine, one year is fine, but two years can mean that the engine oil has become very toxic for your engine.

Another problem with the changing chemical composition of the engine oil is that these processes can produce sludge, varnishes and other unwelcome byproducts within your engine.


The proof.

A good example of this are the late Porsche 996 and early 997 engines which share the same engine oil controlled hydraulic solenoids, in the 996 models with yearly servicing these rarely fail, however in the 997 models with two yearly servicing they fail on a reasonably regular basis, likewise with the cam followers. Repairing these consequences of the two yearly services, even when that is what the service book calls for, can costs thousands of pounds to repair!

Beyond the engine oil, many other items are lubricated during a service, and these lubricants are designed to be re-applied every year at most, which means without regular lubrication the components will fail. A good example are the gear selector cables on Boxster and 911 models, on the pre 2005 models (with yearly servicing) they rarely fail, however on the post 2005 models (with two yearly servicing) we now find we need to replace them relatively frequently.

Another example would be that every 996 or 997 which has suffered bore scoring issues that we have seen, has been one specified with two yearly servicing!


A conspiracy by the manufacturers?

Some would say this is a conspiracy by the manufacturers to make more money on selling parts and repairs out of warranty.

However we believe they are just trying to make the car's seem more attractive to new car buyers due to low servicing costs.

Whatever the reason, the person who suffers is usually the person who owns the car when it is over 5 years old, by which time the damage of infrequent servicing are already done and getting worse every time the pattern continues.


There are many other consequences of not having your Porsche serviced every year.

Another good example might be suspension bushes, if replaced as soon as they become aged or worn, the cost of repairs is just the bushes and labour. However if they are left until they have symptoms obvious to the driver the damage will also be to the tyres, which we all know on a Porsche are not cheap!

The solution to this is to always try to buy a car which has been serviced every year, even if the model is specified by the factory to be serviced every two years, and never buy a car which has had the servicing deferred because it had not covered many miles between services.

Beyond this, even if the car has skipped services in the past, whatever model it is, have it serviced every year and follow the advice of your Porsche specialist of any additional items which need replacement, such as drive belts, water-pumps, coolant, brake fluid, brakes etc.. Not following this advice could cost you thousands of pounds if neglected.

A service is a service wherever it is performed, right?

A last note, it is important who you choose to service your Porsche. Any garage can change the oil in your Porsche, but a true specialist will check much more during the process and know what to look for.

Checking the old engine oil for consistency, smell and inspecting it under a powerful light will warn of many other potential issues with the car, such as early signs of bearing failure, fuel pressure, fuel injector condition and much more, all much cheaper to repair before their issues become more chronic and expensive.

Expert eyes will be looking for common problems with each model and year that an average garage will miss, which will cost you much more money later, if not spotted now.


What else to do?”

Other than all this, enjoy your Porsche, we have found conclusively over the years that the cars which are not used on a regular basis and not driven hard, will suffer more acute problems than those driven hard on a regular basis.. Think of your Porsche as a race horse, it needs to stretch it's legs on a regular basis, otherwise it will stop being a race horse and turn into a stiff old nag!

The Porsche security system in the Porsche Boxster 986 models (up to 2004) and the 996 models upto 2005 can be problematic. When faulty they can cause all kinds of strange behaviour, including winding windows up and down, the car not locking or unlocking with the remote or in some cases with the key even, as well as the car failing to start or any combination of these problems.

To help the Porsche community get to the bottom of problems they may be experiencing, we have written this 996/986 Security system 101 article.

Q: Do all Boxster 986 and 996 models have a factory fitted alarm and immobiliser?

A: All 986 and 996 models do have an immobilser, nearly all of them have a combined alarm and immobiliser (I am yet to see one of the rare ones which has the immobiliser only)

For the purposes of this security system primer, we will assume that all the 986 and 996 models are the versions with the combined alarm and immobiliser.

Over the last 20 years since we first started repairing the Boxster and 996 models, we have had to replace hundreds of key remotes and alarm control units, the details of the inner workings of both are an undocumented mystery with Porsche releasing very few details for obvious reasons.

Without having the proper Porsche PST2 (Porsche system tester two) official diagnostic computer, or one of the later PIWIS or PIWIS2 computers, normally only available at Porsche main dealers, or super-duber independents like JMG Porsche, a new alarm control unit or key remote can not be programmed to work with your car.

Even with one of these super amazing factory tools, you also need special numbers, unique to each car, to program the new control units, previously only available from the Porsche main dealer network.

By the time that 2015 rolled around, Jon Mitchell at JMG Porsche was getting a little bit frustrated. Previously every single component within a Porsche car he had intimate knowledge of just how it worked, from the software within the control units, through to the the engines and transmissions, what he did not like was that it seemed that there was a lack of information about the Porsche security systems, even through the official main dealer information systems... So he set about reverse engineering them which has unlocked all of their inner secrets, but for security reasons, only some of them will be ever released to the wider public.. Hopefully though, these details with help other Porsche technicians and Porsche owners understand the security systems in these cars a little better.

So, in essence, without giving too much away.. How does the system work?

There are three main elements to the security system.

  • The Key with its key head remote (the black bit on the end of the key with buttons)
  • The Key with its transponder (This is buried in the black plastic remote at the end of the key)
  • The Key alarm and immobiliser control unit, both housed in a black plastic box, under one of the front seats, waiting for a bath (more on this shortly!)

The key remote head buttons, and the circuit board under them, along with a battery, are there to lock the car (also setting the alarm in the process) and to unlock the car (and unsetting the alarm in the process), apart from on some versions opening the front or rear luggage area, or in others opening the roof. This is all they do (in simple terms)

The transponder chip, completely unattached to the alarm remote other than being housed in the same black plastic blob with buttons, does one thing.. When you put the key in the ignition, a form of magic (known as inductive loop technology) causes the transponder to have a quick chat with the immobiliser side of the alarm control unit, causing the immobiliser to in turn have a chat with the engine management system, and allow the car to start.

The combined alarm and immobiliser control unit, sitting under one of the seats, apart from unlocking and locking doors, immobilising the engine, stopping the windows from working, allowing the windows to wind up and down, and in some models controlling what the roof is allowed to do, also has one other mission in life, detect water, and once detected, panic, act confused or even keel over and die.

Now to learn a bit more about what makes the alarm control unit to fail, before we move onto the remote controls and their problems.

Under the left hand seat (in a right hand drive UK spec car) sits the alarm control unit, which also houses the nerve centre of the immobiliser.. It sits in a slight depression of the metal floor of the car, which is a bit of a problem, because any water that makes it's way into the car will find that depression and fill it up, damaging the alarm control unit in the process.

Traditionally, the alarm system at this point, will be kaput.. It may still work a bit, it may be doing some strange things such as partially working, intermittently working or the car might just be acting possessed. The alarm might start going off for no apparent reason, the windows might start rolling up or down without you ever pressing the buttons, you might even come back to your car and find it locked, even though you were sure you had locked it, or the remote controls might stop working.

In the past, a kaput alarm would have had one cure... Drying out the water (if it had not done it anyway), solving the leak (often on Boxsters the roof drains) and replacing the alarm control unit and the key remotes, sometimes this could cost anything from £1500 upwards in parts and labour!

Following reverse engineering the security systems, we can in many cases repair the alarm control units (and the leak) and have you one your way again, without having to buy a new alarm control unit, key remotes and paying for programming, we can even do this remotely by post or courier.

Another solution, but one which is very much not recommended, would be to buy a used alarm control unit, keys and engine management control unit from a breaker.. However, this is a very big false economy, as you will no longer be able to unlock the immobiliser or engine management control unit to program a future alarm remote, which is inevitable, without then needing to buy a new alarm control unit, key remote and engine management system, or buying another set from a breaker and throwing the previous ones away. Not only this, but a Porsche specialist or main dealer will no longer be able to perform some specialist tasks to your systems, such as programming them with new software which is released on a regular basis (Such as for running the new fuels with higher ethanol content, as is happening right now!)

What kills the alarm control units?

Water usually. In particular with Boxster models you can almost garauntee that whenever it rains, we start to get calls from Boxster and 996 owners with either misfires, cars that will not start or car's which are behaving unusually.

Typically with Boxsters, 996 models with sun roofs or targa roofs, blocked drains or poor seals cause water to run often un-noticed under or behind the carpet and end up filling the small wells or depressions in the floor where the alarm control unit lives. Either killing it completely, or even just making it do unusual things such as the alarm going off intermittently, the windows doing odd things, the car not starting (either failing to run, or the starter motor not working) among many other failure modes.

In the rain when we get calls about a 996 or Boxster (or other models) misfiring, it is usually down to cracked coil packs.

Next, the remote controls can play up in a number of ways...

If you find your Boxster or 996 alarm has stopped remotely unlocking and locking the car via the buttons on the remote control, there could be a number of problems causing this apart from a bad alarm control unit.

The Remote Battery.

In the alarm key remote is a small battery, often, replacing the battery will solve problems with the buttons not locking or unlocking the car, try this first. If you have not replaced your batteries in a year or two, they probably need doing anyway!

The Remote control's computer chip has frozen or crashed.

A few years ago Porsche were so swamped with warranty replacements of the key remotes that they issues a technicial service bulletin (TSB) explaining how to reset a remote control which had crashed or frozen, the process is simple..

  1. Remove the battery from the key remote
  2. Insert the battery the wrong way round, flip it, so the writing is facing the other way. Do not worry, this will not damage the remote.
  3. Press the unlock button continuously while jumping on one foot for sixty seconds (Jumping on one foot is optional but helps pass the time and helps with fitness)
  4. Flip the battery back around the right way.
  5. Try the remote control again, if this works you can be sure that the remote had crashed/frozen and you successfully reset it.

The Remote control has become out of sync with the alarm control unit.

Through reverse engineering the software inside the alarm control unit, we were able to de-cypher how the alarm control unit and the key remote talked and how the rolling codes worked.

Rolling codes are not top secret information, they are used in just about every alarm system remote control in the world, both in systems designed by car manufacturers as well as with after-market car alarm system manufacturers. In essence, every time you use the remote control to lock or unlock the car, the alarm system and remote control have a little chat and do not disclose all the details of a very special long number that they both have stored, they just ask one-another mathematical questions about part or parts of the number, and if both of them feel happy about the conversation, they then agree to lock or unlock the car.. Once they have done this, they both take their number and encrypt it slightly to change it for next time, but without ever again disclosing to the other what the new number is.. It should always match as they will have mashed up the number is a very specific way. However, sometimes problems occur.

Potential causes of the alarm system and remote control going out of sync are numerous, they can include the weather, radio interference (such as even a taxi driving past with the driver using a two way radio) or even you being just on the cusp of being close enough or too far away from the car when you used the remote.

In rare cases like this, the key remote or the alarm system may have mashed up it's code to a new version, without the other also doing the same. This is in effect what causes the remote and alarm going out of sync.

Anyway, as we mentioned, at JMG Porsche we reverse engineered the alarm system hardware and software, so discovered a little known and undocumented process to re-sync the alarm control unit and the key remote.. There is a proviso, if the two have gone out of sync by too many steps, the damage has been done and the two will never be able to be sync'ed up again, even with our amazing abilities at JMG Porsche.

The process to re-sync the remote key head is as follows.

  1. Put the key manually into the door lock (it does not matter if it is already locked or unlocked.
  2. Press the lock/unlock button and hold it in.
  3. Turn the key to the lock position and back to the middle position five times and return to the middle position one last time.
  4. Let go of the lock/unlock button.
  5. Press and hold in the lock/unlock button again.
  6. Turn the key to the unlock position and back the middle position five times and return the the middle position again.
  7. Let go of the lock/unlock button.
  8. Press the lock/unlock button in again and hold it in.
  9. Turn the key to the lock position and back to the middle position five times and return to the middle position again.
  10. Take the key out of the door lock and try the buttons.

If the buttons now work, you have successfully re-synced your alarm system control unit and keys! Well done, go and pat yourself on the back and drink a well deserved beer/coffee/tea/vodka (delete as appropriate) while you reflect on how the key remote might have gone out of sync... Are you a persistent key in pocket fiddler? or did you let your young son or daughter play with your keys? If so, stop it! Or at least now you know how to fix it if it happens again.

However, this will only work if the key remote and the alarm control unit have only stepped a couple of steps out of sync with the alarm control unit, if you are a supper "key in pocket fiddler" or your child has played with the buttons to such an extent that the codes have rolled more than a couple of times, then the key may now be so far out of sync, nothing will bring it back.

Faulty Remote Controls

They are pretty robust units really, but even a Porsche key head remote controls can eventually fail, here are some failure modes.

  • Main circuit board failure - This could be as simple as a "dry joint" needing re-soldering, or a crack in the board which may or may not be repairable.
  • Button failure - Usually the buttons fall apart because the plastic outer casings button area cracks, causing the button inside to move slightly sideways, rather than just in and out. These can be repaired with a new or used button soldered into the old ones location, and new upper outer shells are available to fix the actual cause.
  • Water damage - The remote control key heads have a rubber seal, if when you change the battery this is not re-fitted or if it breaks with age, damp gets in and can destroy the remote. Usually you will see water damage on the circuit board.
  • Designed in planned obsolescence - This I feel is a little bit naughty of the designers, or a very simple honest mistake in design. Once the code in the remote has rolled a pre set number of times, after literally hundreds of button presses, it will not be able to roll any more due to how the software was programmed. The alarm system however will continue to roll the code into infinity, so eventually they will go one step out of sync and the love affair between your remote key head and the alarm control system will be over forever.

What can JMG Porsche do to help?

Apart from writing this article so that owners, enthusiasts and even Porsche technicians can understand the system a little better, we have a few things that we can do in house to solve your alarm system problems.

What we and the Porsche main dealers can do, as well as probably a few specialists.

  • Programming a new alarm key head remote to your existing alarm control unit.
  • Programming a new alarm control unit along with new key head remote controls.
  • Diagnosing a problem with the alarm control unit or key remotes.

What we can do that the main dealers can not do and potentially no one else in the world can do in some cases!

  • Repairing and refurbishing your current key head remote
  • Repairing and refurbishing your current alarm control unit
  • Programming a new alarm control unit with your old key remote keys that worked with the old one
  • Re-programming a used second hand alarm control unit to work with your car and your key remotes
  • Re-programming an incorrectly programmed control unit to be a new virgin unit again, or with the correct data (Useful for other Porsche technicians who have hit the wrong button or experienced power failure during programming)
  • Extracting and decoding the unique to your car's Porsche security data needed to program a new control unit, from an old dead control unit
  • Extracting and decoding the unique to your car's Porsche security data when Porsche do not have it available (such as with the RUF manufactured Porsche models where Porsche do not have the right data)
  • Programming a new alarm control unit on the bench, without ever seeing your car in person, we just need your old alarm control unit, keys and ideally your DME (Engine management computer) Which is useful for those who want to save the labour costs of a Porsche technician to remove the old control unit and fit a new one.

What we can not do..

  • Program any random key head remote to your car, it needs to have been previously working with the old control unit at time of failure

What we will not do, even if we can!

  • Send you out a new alarm control unit and key remote for a car with just the chassis number unless you provide adequate proof of ownership (A legal authority document such as a log book/V5 (UK) title deed (USA) and a the address of this document has to match the postal address we will send it to.
  • Educate or pass on what we have learned from reverse engineering the security systems to any third party other than the information on this page. A software engineer knows the decryption routines but does not know what they are for, an electronics engineer knows the methods to extract the required scrambled data but again does not know what the circuit boards do, and only Jon at JMG knows the full process and processes the repairs. Anyone trying to approach Jon asking or probing for more information will result in the Police being informed. No documents, printed or in data form exist to help anyone else crack the system, so unfortunately the exact process will die with Jon.

What can be done to protect a 986 or 996 from the alarm control unit getting water damaged in the first place?

  • Good idea - Getting JMG Porsche to install their 9x6 alarm system drainage port modification to your floor, they let the water out, but do not let it in!
  • Good idea - Getting JMG Porsche to install their 986 improved roof drainage system to your Boxster
  • Good idea - Routinely check your roof drains for leaves and general debris which accumulate there and remove and clean them, or ask your specialist to do this a couple of times a year for you. It only takes half an hour to an hour in labour and can save you a fortune!
  • Bad idea - Fitting a sealed box or bag around the alarm control unit, these rarely are 100% water tight and will often allow water in, but not let it out, so you end up with small amounts of water accumulating over time in the sealed enclosure, but with not enough ventilation for it to evaporate away, until eventually there is enough water to damage the control unit, which can happen in cases where the amount of moisture would not have been enough to cause damage on its own.

And what to never do?

Never, every buy a "set" or "kit" containing an alarm system control unit, DME (engine management computer) and key remotes from a Porsche salvage business and fit them to your car.

  • The software in the DME may not be right for your engine, causing all kinds of unseen problems.
  • The identity of your Porsche will not match the Porsche database IPAS Codes, meaning that you will NOT be able to program new keys without having to buy a new alarm control unit, DME and key remotes, at a massive cost. Which with a used key remote, is very likely to happen at some point, potentially very soon!
  • You will not be able to have your DME reprogrammed over time, such as the roll out of high ethanol fuels which is happening now..
  • Your Porsche identity in your control units will not match your car's actual chassis number, you may encounter insurance problems or even end up in hot water with the Police and have to prove the identity of your Porsche is that of the chassis number, such as via a VIC check, which your Porsche will fail due to chassis number mismatches in the various control units versus the number plates worn and the chassis number stamped into the shell. (There have been a number of Porsche that have ended up on Q plates and a dodgy HPI history due to this kind of problem!


A last amusing fact.

Someone at Porsche decided after the 996 and 986 models that perhaps putting the alarm control unit in a depression in the floor, likely to fill up with water was an especially bad idea, so in the 987 Boxster and Cayman models, as well as the 997 models, they moved it away from the floor level and renamed the system as the Porsche Access System (PAS)..

This was a great idea..

Until someone else at Porsche, potentially looking for a good place to put the new "Rear Body Control Unit" (that was a new feature of these cars), had a eureka moment and decided to put this control unit in this really useful empty place under the seat... So if you own a Porsche 987 Boxster, Cayman or 997 and are wondering why your rear lights are doing odd things (brake lights on all the time, reverse lamps on even when not in reverse) or the roof has an interest in suddenly moving up or down, even if locked in position, snapping control rods in the process, then your rear body control unit has probably flooded in exactly the same way that the old alarm control units used to on the earlier model... That is progress for you!



This is not going to be an article about how to change your cam and balance belt on a Porsche 944 or 968, this subject has been covered elsewhere on the internet and personally, it is one of those jobs where if you have not been trained to do it, are not experienced in doing it, you should not do it.. An apprentice at JMG Porsche is not allowed to change a 944/968 cam or balance belt until they have their basic first two years of training under their belt, after that they are supervised on the first few and on probation for the first 4 years with them being checked... So in short, get a pro to do it, ideally a specialist with in depth knowledge of the 944 and 968 engines.

Over the years I have often been asked how often they should change their cam and balance belt on their 924S, 944 or 968, and my answer is "Every 4 years" and change the water pump, front engine oil seals, belt tensioners and rollers every 8 years!

The following questions and answers are here to explain why I advise what I advise and is actually a cut and paste from a recent answer by myself as a technical advisor to the Porsche Club of Great Britain, as a response to a question on their forum.

To an extent, the same advice applies to any belt, on any car, so a Boxster, Cayman or Cayenne/Macan/Panamera or 911 (996, 997, 981 or even air cooled cars) which as a whole do not have cam belts, but do have auxiliary drive belts which if they fail will at best leave you stranded, but at worst can damage the engine or even the bodywork of the car (belts at high speeds make a mess!)

Other than not having a balance belt, the Porsche 928 advice would be the same advice as for the 924S, 944 and 968 owners. 

What destroys a belt?
From education training and experience
* Entropy (Everything wants to return to its original component materials) - Very slow
* Oxygen (Oxidises the rubber from the outside inwards, forming cracks eventually, which then allow more oxygen deeper into the belt)
* Wear (Accelerated if the tension is too high or too low)
* Incorrect installation
Who makes the belts for Porsche?
Over the years I have seen the following belts in Genuine Porsche boxes.
* Dayco
* Gates
* Bosch
* Continental
How long can an incorrectly setup or installed belt last?
* As little as a few seconds
* As long as a correctly installed belt
Depends on how incorrectly it has been installed or setup (I have seen many weird things going on in 944 belt covers)
What else accelerates belt degradation?
* Contamination from oil
* Contamination from power steering fluid
* Contamination from coolant
* Contamination from dirt/grit
* Contamination from fuel
* Contamination from plastic dressings
* Contamination from sprays such as WD40
* Ionisation of the air in the cam belt cover
How soon can a correctly tensioned good quality belt without contamination last?
* Soonest I have seen is 5 years with a missing ionisation cap.
* Soonest I have seen with no visible signs of cause - 6 years
* Oldest belt that I have seen break was 26 years old!!!
When would I change the belts on my own 944 fleet?
* Every 5 years without fail and I check inside the cover every year for contamination or issues and always check for leaks every time I drive them.
When would I recommend customers change them?
* Every 4 years (as you might not have your belt, oil seals and leaks checked so often as I do)
How much damage is caused by not changing them?
* Wrecked cylinder head (Valve contacts and bent/detaching valve heads)
* Wrecked pistons (Valve contact, sometimes with valve heads detaching and bouncing around!)
* Wrecked cylinder block (mushroomed out pistons split the bore)
Other advice.
* Change the water pump, tensioners, rollers and front engine oil seals on every second belt change. The water pump can fail through age as well as mileage, as can the seals and tensioners/rollers. Any of these parts can cause the belt to fail.
* Make sure your car has an ionisation cap between the distributor cap and upper front cam belt cover.
This is an important one.
When the 944 was designed, it had a hose that ran between the cam belt cover and air box.. This was to bring fresh air through the belt covers, and remove air which had been ionised by the electrical activity within the distributor cap. There was also a plastic cap between the distributor cap and the cam belt cover, to reduce the amount of contamination of the air within the belt cover with air ionised within the distributor cap.
In about 1988, Porsche eventually go to the bottom of why so many 944s suffered with hydrolocked engines following driving through deep puddles or crossing a river/ford crossing... It turned out that as soon as water was sprayed around the front crank pulley, or the pulley entered water, the water would go into the belt cover and the balance belt would throw this water directly at the vent port which had the hose to the air box.. Once the air box contained a certain amount of water, or you turned a corner, the water would flow through the airflow meter, and get sucked into the engine... Nasty.
Porsche then issued a TSB to say that all Porsche models should have this hose where fitted (important) and a blanking plug fitted (Not so important, I leave them open for ventilation on the advice of my mentor at Porsche).
The problem with this deleted hose, is that without it, it is even more critical to have the ionisation cap installed. They are cheap and available.
That is all :)

At this time of year, JMG Porsche get many more phone calls and emails regarding faults caused by the Porsche factory alarm system, which are often connected to damp weather

Unfortunately the traditional repair is often a new alarm control unit and new key remotes, which can become an extremely expensive repair of between £1000 and £1500. But do not panic, there is an alternative!

At JMG Porsche we spent much of 2015 and 2016 reverse engineering the Porsche alarm system and keys, and we believe that we are potentially the only people in the world, outside of the companies who developed the original systems for Porsche, who understand fully how these systems work. The result is we can not only repair these units, but beyond that we can also save you money by recycling your old keys to be used with your repaired or even new alarm control unit!

If your old control unit can be repaired, we can repair it with new components.

If your old control unit is beyond repair, we can even re-program your old keys into the new control unit (A worldwide first!)

Not only this, for the DIY mechanics out there, but we can even perform these repairs by mail-order, so wherever your car is, we can provide a repair service, or reprogramming of your car, without even needing to see the car!

If you are suffering from any of the following issues, please make sure you get in touch with us first!

* Door windows raising or lowering by themselves

* Alarm system going off for no reason

* The roof trying to move by itself, possibly even breaking pushrods in the process!

* Brake or reverse lights being illuminated when they should not be

* Doors not unlocking by use of the key

* The car failing to even try to start (No starter motor noise)

* The car failing to start and run (Starter motor noise but the car does not start)

Any of these faults can be caused by the alarm control unit!

If you are suffering from any of these problems, please call 01202 488800 or email This email address is being protected from spambots. You need JavaScript enabled to view it. to arrange for diagnosis and repairs! 

Published in JMG News

UPDATE - Free service suspended during the COVID19 crisis, but still available for a fee due to the logistics involved in providing this service safely. ****

It is often inconvenient and a logistical nightmare getting your Porsche to a garage for servicing and repairs.

With this in mind, JMG Porsche are now trialing a new scheme where we will collect and deliver cars free of charge within a 10 mile radius of our workshop in Ferndown.

For customers working or living within 10 miles of our workshop, you have two convenient options.

  • Home or your place of business handover - We will collect the car from you at either your place of business or at your home, once it is ready you can pay your bill over the phone, and we can deliver the car back to you at the same location that we collected from.
  • Workshop handover with being driven to and collected from your home or work - Come to our workshop to drop off your car, discuss the repairs over a coffee, we will then drop you off at home or work and collect you again when your car is ready.

For customers further afield this opens up two convenient options.

  • Train Station handover - Meet us at the train station, we will bring the car to our workshops, while you catch the train home. Once the car is ready, pay your invoice over the phone, catch the train again and we will meet you at the train station ready for you to drive hom.
  • Workshop handover with you being driven to and from the station - Come to our workshop and discuss your repairs over a coffee, we will then drop you off at the train station so you can make your way home. Once your car is ready, we will again collect you from the train station so you can collect your car from the workshop.

Alternatively, you can still use the old method of getting the car to us and suffering the inconvenience of having to find friends or family to follow you over for when dropping off or collecting your car. For some people this may offer you the ultimate in convenience as you might need to leave your plans until the last moment at a time where we may not be able to collect it.

Terms and conditions.

As is usual these days, there are a few terms and conditions for our car collection and delivery service.

  • Our drivers are a limited resource and may at certain times of the year be booked up days or weeks in advance, so it may be essential to book your collection and delivery service, along with the work to be performed a couple of weeks in advance.
  • We will need to know that you require this service in advance of the day the work is to be performed, otherwise we will assume you will be dropping the car off to us.
  • At time of booking this service we will require a £30 non refundable, but transferable, deposit. Even though this service is free of charge for many, there are costs to the business associated in collection and delivery of you or your car, which in some cases may be Taxi fares, fuel or parking charges, as well as the time of the employee. Should you not notify us before the staff member has left for a drop off or collection, that you will not be there or available, this deposit will be retained to cover these costs. However, should you be able to offer us a couple of hours notice that you will not be there, we will hold the deposit for the alternative time that you request. When you come to pay your invoice, you will notice the deposit will be listed, and as long as work has been performed on your car, you will also see the deposit deducted against the invoice.
  • This service can not be used in conjunction with other promotions, such as with club discounts, free-new-customer-inspections, discount vouchers or competition prizes.
  • Collection and delivery services will usually be limited to outside of rush hour times, such as only being available between 10am and 4pm on week days. However if this is not convenient to you, please explain your situation to our service manager, who has the power to change this policy on a case by case basis.
Published in JMG News


We are open, but experiencing overwhelming call volumes.




Please email us if you need to contact us, do not call, we are unlikely to be able to answer the phone and voicemails are backing up.

Please also do not visit the workshop, unless you have an appointment to drop off or collect your car.


At this time of year, starting at the end of February, we are usually booked up far in advance, with customers anticipating the return of springtime and getting their Porsche out of hibernation.

However this year there has been several other factors which have seen that demand multiply by a factor of ten with telephone enquiries.

These factors include a few Porsche personalities mentioning us in their media (videos and articles) which has driven demand for our services, but also a couple of years ago Porsche Centre Bournemouth moved into their new building on the same road as us, which has also caused an increase in awareness of JMG Porsche and therefor a constant rise in enquiries.

Our priority has always been with working on cars already here, and cars already with appointments booked in.

So staff answering the phone, would be taking them away from dealing with cars already here.

If we hired temporary staff to answer the increased call demand, this would result in higher costs, and therefore higher hourly rates. Besides, we would probably need 5 to 10 additional staff to just answer calls at the moment, and those staff would probably have to keep asking other existing staff members for answers to questions from the phone calls that they answered, This would be as bad as the staff here answering the calls anyway, distracting them away from working on cars, and therefore not completing that work on cars already here.. So not a real solution.

This should settle down over the next few weeks and normal service will resume, but as always we are likely to still be booked in advance for about 4 weeks at any one time, but at least we will be able to start clearing the backlog of customer voicemails and lower priority emails.

However in the longer term, we will be looking into a solution for the problem of demand (customer enquiries) outstripping supply (our time) as what would look like the easy solution of just hiring more technicians and receptionists, rather than hiring the best additional technicians and receptionists, would degrade the business and lower the quality of what we provide.

However, if you are a technician with Porsche experience, we are always interested in hearing from you, as long as you have the drive to become the best at what you do and perform your work with the best quality and workmanship possible.

In the interim, if you need us, please email us

service "at" jmgporsche.co.uk



JMG Porsche, Independent Porsche specialists for modern classics through to the very latest models.


Porsche servicing, diagnosis, repairs and modifications.


With our roots going back to the early 1970's, we are a family run independent Porsche Specialist spanning three generations.

We have the same or better equipment, training and technical information access as enjoyed by the main dealers, while remaining friendly, honest and with a common sense approach.

Call us on 01202 488800 or email This email address is being protected from spambots. You need JavaScript enabled to view it. with your requirements.








Published in Frontpage Content

Following on from our other diagnosis articles, in this article Jon Mitchell is going to talk a little about exhaust emissions.

As we go crawling inside the exhaust of a Porsche, we will take a look at the exhaust emissions, what each of the gasses are, what effect they have on your engine and how they effect the environment.

Exhaust Emissions.

The normal air that we breathe is 80% Nitrogen and 20% Oxygen, with a varied trace of other gasses.

Petrol is a hydrocarbon fuel, comprised of a mixture of carbons and hydrogen. If our engines were 100% efficient, burning all the fuel completely, the oxygen would combine with carbon to form carbon dioxide (C02) and with hydrogen to form water (H2O). The perfect engine therefore would inhale a perfect mixture of air and fuel and exhaust carbon dioxide and water. For every gallon of fuel burnt, a gallon of water would be produced and once the engine was warmed up, the water would exhaust as steam.

Unfortunately a perfect engine does not yet exist and combustion is always to an extent incomplete, in reality the engine in your Porsche will consume close to ideal ratios of fuel and air but will exhaust various compounds including hydrocarbons, carbon dioxide, carbon monoxide, oxides of nitrogen, water vapor and even oxygen.

Most of these gasses are relatively harmless in the quantities that are exhausted by a single Porsche in an open space. In an enclosed space some of them become deadly. However when millions of cars around the world are exhausting these compounds the accumulated effect is harmful to the environment.

So lets take a look at some of these gasses in more detail.


Carbon Dioxide

One molecule of CO2 contains one atom of carbon and two atoms of oxygen. CO2 is chemically stable and does not easily react with other substances. It is not poisonous, it is produced by all animals that breathe, including fish. Oxygen is inhaled and Co2 exhaled at a concentration of around 5%.

CO2 is absorbed by all green plants by a process of photo-synthesis which only happens during daylight hours, which also produces and releases oxygen.

A combination of the loss of the rainforest around the world, along with the increased production of CO2 by population, cars and industry, is a concern as CO2 helps trap heat within the atmosphere.

CO2 is a byproduct caused by combusion.

Within an engine the levels of CO2 is likely to be between 13 and 15% with a correctly running engine with a correct air fuel ratio. Less than 8% would indicate an improper air fuel mixture, a missfire or leaking exhaust. Above idle speeds CO2 is likely to increase by around 2% because of the increased RPM causing higher efficiency.

Carbon Monoxide

Carbon Monoxide or CO is a very poisonous substance and accounts for around 47% of all air pollution.

CO is also an exhaust emission that is tested for during a UK MOT test. Elevated levels of CO will cause an MOT failure and the levels set by VOSA (The official body of the MOT Test) varies from car to car, dependent on the manufacture date of the car, as well as what equipment is installed.

CO can be deadly to people, if breathed for a sustained period it joins to red blood cells, blocking the path for oxygen molecules, eventually causing death.

CO within the exhaust would indicate incompletely burnt fuel. There will always be a component of CO within an exhaust

High levels of CO are normally caused by to high a fuel quantity being consumed for the amount of air combined with it. This could be caused by a blocked breather, clogged air filter, high fuel pressure a worn camshaft, faulty air flow metering or faulty exhaust gas sensing.



Petrol is an almost pure hydrocarbon, another name for hydrocarbons would be its chemical symbol which is HC.

Hydrocarbons within the exhaust indicate unburnt fuel and are measured in ppm or parts per million.

Hydrocarbons as you can imagine can be raw fuel that is atomised or vapourised, as well as being chemically altered ingredients of the original fuel. They can be extremely dangerous to the eyes, nose and lungs.

Hydrocarbons when combined with high NOx (Oxides of Nitrogen) and sunshine, cause photochemical smog to form in the upper and lower atmospheres. Not such a problem in the UK, but in California it has been a massive problem for many years.


Lead used to be used in fuels as it lubricated valves, prevented detonation.

Lead is a celular poison for blood, bone marrow and nerve cells. Lead has not been available in mainstream fuels for some time, and even when it was last available in forecourt fuels it was in minute quantities compared with the 1960's and 1970's.

All Porsche models made since the 1960's can run without lead in the fuel in standard specification. Typically cars with cast iron heads require conversion and all Porsche models have aluminium heads, which already have hard valve seats and valve guides not requiring lead in the fuel.


Oxygen, or O2 (its chemical symbol) consists of two Oxygen molecules and is measured in % of volume.

A very small percentage of O2 will be within the exhaust of a correctly fueled and performing car, as combusion will never be complete and too little oxygen would cause higher hydrocarbons or CO. Typically O2 levels will be around 1 - 2% by volume, pre catalytic converter.

If the O2 level is higher than this, typically it may mean that there is an exhaust leak or the mixture is too lean (may also have high hydrocarbons in some cases).

Oxides of Notrogen or Nitrogen Monoxide and Nitrogen Dioxide, Nitrogen Nitrate.

NOx as it is also known is formed through high pressures and high temperatures.

The N symbolises one Nitrogen atom combined with oxygen atoms (the O), the x symbolises the number of oxygen atoms combined to a nitrogen atom.

NO is Nitrogen Monoxide. Which is one Nitrogen molecule linked to one oxygen molecule. Another name for this is Nitric Oxide. It is caused by by combustion temperatures rising above 1370 degree c.

Typically Nitrogen monoxide, especially at higher engine speeds and loads, causes the production of Nitrogen Dioxide (NO2), Nitrogen Nitrate (NO3) and Ozone (O3). Nitrogen dioxide often forms a brown fog, which is the typical smog that Californians complain about.

One annoyance is that NOX emissions can be caused by high performance engines, especially at their peak efficiency with at cruising speeds with a perfect air fuel ratio (AFR). A way of reducing NOX is to recirculate a small amount of exhaust gasses into the combustion chamber, which reduces combustion temperatures and therefore NOX emissions. However, it also reduces power, so is often employed only in cruising conditions or in conditions tested by government bodies.

Solutions for the engine designer.

Now that we have dealt with the exhaust emissions exhausting directly from the engine, we can cover some ideas and methods of reducing emissions employed by modern engines.

Catalytic converters

All modern cars are fitted with a catalytic converter. Also known as a Catalyst or Cat.

Since January of 1993 all UK cars have been fitted with a catalytic converter.

The principle reason for the use of catalytic converters was to complete the combustion of the exhaust gasses so that they are less polluting to the environment.

A Catalyst is something which promotes a chemical reaction without itself being effected. On a car it works as a secondary combustion chamber to complete the combustion of anything left over after the primary combustion has taken place.

At 300 degrees C the catalytic converter begins to work, its happiest temperature is between 400 and 800 degrees, where it will be most efficient, once the catalytic converter passes 1000 degrees, some of the precious metals within the catalytic converter will begin to break down and melt.

When working in the correct temperature range, with the correct levels of exhaust gasses entering it, the catalytic converter will convert CO and HC into H2O and CO2. NOx is reduced by a process of reduction where oxygen and nitrogen are forced apart. The Oxygen combines with CO to produce CO2 and N2.

A weak mixture with a high level of O2 is good for the oxidation of CO and HC. On the other hand, a rich mixture with some CO aids the reduction of NOx. A comprimise is reached by the engine running at a mixture of 14 to 1. This means the engine is slightly richer than ideal and use more fuel, but it will reduce NOx emissions, yet will be lean enough to combine CO and HC to create H2O while also running the catalytic converter hot enough to stay within its ideal temperature band. Often with modern engine management the engine will quickly alternate between slightly rich and slightly lean to allow the catalytic process to get the best of both ideals.

H2S is a gas not tested in the UK for MOT testing, but is often released by a new catalytic converter, which causes the smell of rotten eggs that can sometimes be smelt with a new cat. However sometimes with a car running rich will also cause this smell on the overrun as it becomes lean and the catalytic converter creates this gas as a byproduct of burning off excess carbon caused by the rich state.

A car fitted with a catalytic converter has to run perfectly at all times, a misfire, sensor fault, wrong fuel pressure, or many other, can permanently damage the catalytic converter. As an expensive item it is wise to follow a specialists advice with preventative work on the engine, before it becomes a fault, but also if you experience a fault, to have it attended to immediately.


As the engine operates, air and fuel are mixed together, drawn into each cylinder. The Air Fuel Ratio (or AFR) at which air and fuel burn at their most efficient is known as the Stoichiometric point and is where HC and CO should be at their lowest and CO2 should be at its highest. This ratio is 14.7:1 by weight, and it is also called Lambda = 1 which is the greek word for "correct".

Various fractions of Lambda can can be converted into AFR by multiplying 14.7 by the fraction. The AFR/Lambda chart is the result.

Although lambda=1 is not the ideal point fuel consumption, it is the best comprimise for using a catalytic converter to oxidise CO, HC and NOx. Therefore if the Lambda can be kept between 0.98 and 1.02 the efficiency of the catalytic converter will be in excess of 90%. The reason being that the lower emissions from the engine reduce the work required for the catalytic converter to convert these harmful gasses into more acceptable ones.

Oxygen Sensor

A sensor placed within the exhaust system to sense the levels of oxygen present following combustion, the Oxygen Sensor is known by many names. Including the Oxygen Sensor, Lambda Sensor, Exhaust Gas Oxygen Sensor (EGOS) or even when used with a heating element a Heated Exhaust Gas Oxygen Sensor (HEGOS). For the purpose of this article, we will stick with calling it the Oxygen Sensor.

The sensor typically has a porous ceramic tip, this tip often contains two platinum electrodes, the outer surface electrode is exposed to exhaust gas, with the inner electrode exposed to atmospheric air. The difference in oxygen content between the two electrodes produces an electrical voltage, which is read by the engine management computer to analyse the oxygen remaining in the exhaust after combustion.

The sensor is often placed before the catalytic converter for the engine management system to evaluate and adjust the mixture being fed to the engine, however more modern cars now also have one after the catalytic converter, which allows the engine management system to know how efficiently the catalytic converter is performing.

The voltage generated by an oxygen sensor is inversely proportional to the difference in oxygen content seen in the exhaust compared to the oxygen in the ambient air around the car. The engine management system will use this signal to increase or decrease the fuel provided to the engine on a split second by second basis, in effect allowing the engine to be self tuning.

Typically voltage being seen by an engine management system would be between 0.1v (lean) and 1.0v (rich). If you were to connect a volt meter to the lambda sensor while the engine is running, you would likely see the voltage changing from above and bellow 0.55volts on a regular basis, possibly to quickly for the volt meter to be able to display, in which case an average voltage of 0.55 volts may be observed.

Analysing the quantity of oxygen remaining after combustion is an excellent indicator of how rich or lean the mixture of fuel is being supplied to the engine. In theory an engine management system could solely use an oxygen sensor to decide on the quantity of fuel to inject into the engine, keeping the exhaust gasses constantly at the correct oxygen content indicating a proper mixture, which in turn would extend the lifespan of the catalytic converter and the oxygen sensor, while also providing a reasonable fuel economy. However, a car requires different levels of fuel for different driving conditions and demans, such as accelloration or decelloration, on full throuttle or part throttle, if the mixture remained at 14.7 to 1 at all times, the car would drive very poorly. As such, engine managements tend to only take notice of the oxygen sensor when cruising at a constant or near constant speed.

More recently a new type of oxygen has been available, known as a wideband sensor, which is able to read a wider range of air fuel ratios, which an engine management system can monitor and compare with target air fuel ratios at a wide range of demands and conditions to make alterations to fueling. These are also used by enthusiasts and tuners so they can monitor their exhaust oxygen content as a warning instrument as well as a tuning device.

An oxygen sensor can however be fooled. A perfect air fuel ratio may for one reason or another not fully combust both the fuel and air mixture, the oxygen sensor will see this surplus fuel, which may be interpreted as a weak mixture, especially dangerous if using an oxygen sensor to tune a car.

Mass airflow sensor (MAF Sensor)

A mass airflow sensor (also known as a MAF sensor) is a sensor sometimes used by an engine management system to measure the mass of air being consumed by the engine at any one moment in time.

As the fuel pressure and the flow from fuel injectors is usually predictable as to how much fuel will flow through them per second, knowing the correct amount of air entering an engine can provide a good assumption of how long to pulse the injectors open for, to provide the correct air fuel ratio for any one given engine speed or loading. In systems with a MAF sensor, often an oxygen sensor is also used, especially in catalytic converter equipped vehicles to provide perfect fueling in all conditions. However a faulty MAF sensor may cause the engine management system to believe there is a fault with the oxygen sensor, or indeed the other way round.

Air flow meter - Also known as a Volumetric Air Flow Meter (VAF Sensor)

Before MAF sensors were invented, the common way to measure fuel entering a fuel injected car was by using a Volumetric Air Flow sensor. When coupled with a temperature sensor, a VAF sensor can make a good approximation of the volume and mass of air entering an engine. However, their design, owning to a spring loaded trap door connected to a sensor causes this to be a component which is not only subject to wear, but also an item which offers resistance to air entering an engine, lowering performance.

Manifold Absolute Pressure Sensor - Also known as a MAP sensor

A map sensor measures the air pressure seen at the intake manifold, as the amount of air which can pass a throttle butterfly at any opening position is fixed, the combination of MAP sensor with a throttle position sensor, can also make a good aproximation of the volume of air being consumed. When combined with a temperature sensor, like with a VAF sensor, the engine is able to calculate the mass of air being consumed and calculate the fuel required for any given demand placed on the engine.

Turbo charged vehicles sometimes are fitted with both a MAF and MAP sensor to provide increased accuracy as well as telling the engine management system how much boost is being provided by the turbo or turbos. This is sometimes essential as the requirement for fuel alters with the pressure it is being compressed to. Typically, higher intake pressures require an increase in fuel quantity to avoid damage to the engine and provide maximum efficiency.

Engine Coolant Temperature sensors

Engine coolant temperature sensors are essential to the smooth and safe running of an engine. When an engine is cold, the requirement for fuel is higher than when one is warm. In addition a catalytic converter will not work until it has reached a temperature of above 250 degrees C, which means as well as an engine management system using the engine temperature to increase or decrease fuel quantity, it will also use it to know when and when not to take notice of the oxygen sensor.

Closed Loop or Open loop.

When the conditions are right, an engine management system will begin to rely on a oxygen sensor to calculate and govern the fuel quantity provided for the engine. When this is the case the condition is known as closed loop. Typically this will be when the engine has reached opperational temperature, the throttle is neither at wide open throttle nor closed at an idle position. When these conditions are not all made, the engine management system will be known as running in open loop mode.

Engine Management System (EMS), Electronic Control Unit (ECU), Digital Motor Electronic (DME)

There are many names used for the electronics used to control and engine management system as shown in the title of this section. However for the sake of this article we have referred to the Engine Management System or EMS. However all the names mean the same thing, a sophisticated (for its day) computerised control unit which monitors several sensors, decides how much fuel to supply, when to supply an ignition source (spark) along with a few housekeeping tasks and sometimes recording faults found. One of the important jobs is to ensure the car runs efficiently and with the minimum of exhaust gas emissions.

Faulty Engine

An engine fault can cause problems with exhaust emissions. A good example would be wear causing a loss of compression, which may cause the assumptions of the engine management system to be wrong and therefore the wrong quantity of fuel provided, which can result in high levels of CO and possibly hydrocarbons. In addition, and engine which burns oil can sometimes cause a raised level of hydrocarbons, which is because like the fuel you intend to use, the engine oil is a complex carbon and fuel source, which when incompletely burnt, will cause hydrocarbons and in some cases raised CO levels depending on how well it is being combusted.

Exhaust System

A faulty exhaust system may have a leak. Often you will hear people refer to an exhaust blow, but not so many people know that this will also cause air to enter the system.

For every combustion event there will be a high pressure wave traveling along the length of the exhaust, causing some exhaust gasses to possibly escape before they have reached the tailpipe. However behind each one of these high pressure waves there will also be a lower than ambient negative pressure wave, which will suck ambient air into the exhaust.

If the exhaust leak is before the oxygen sensor, the sensor will see this additional air entering the exhaust as a lean mixture, possibly causing the engine management computer to increase the mixture provided to the engine.

If the exhaust leak is after the oxygen sensor, the sensor will be oblivious to the additional air, but any diagnostic work performed by measuring the exhaust gasses at the tailpipe will be false, in particular the oxygen level.

The MOT Test

Typically, the MOT test in the UK is interested in CO, HC and O2 levels in the exhaust system, elevated quantities of any of these, beyond pre set limits will cause a failure of the UK MOT test.

Diagnosis - Hydrocarbons.

Typically, hydrocarbons are caused by an incomplete burn of the fuel provided to the engine. Normal causes of this will be poor ignition, improperly atomized fuel, consumption of engine oil or an incorrect mixture. As such, diagnosis needs to focus on engine health, ignition, fuel system health and other exhaust gasses which are present.

With hydrocarbons many garages will try to say it is a mixture problem, however unless the mixture is extremely over lean, hydrocarbons will more often be caused by something stopping that cylinder from firing correctly, leaving fuel left over. Often a rich mixture will fire correctly, however will result in high CO levels.

So if you see normal CO levels but high hydrocarbons, then the problem is probably a ignition or engine fault.

If you see low CO levels (lower than reasonable) and high hydrocarbons, the problem is probably one of the mixtures being too lean, so look into that.

If the CO levels are very high and you also have elevated hydrocarbons, the problem may well be the high mixture levels (too rich)

Overall, Hydrocarbons are one of the most important exhaust emissions to help point at the cause of an issue, if the hydrocarbons are low, it normally indicates a good ignition system as well as a fit engine.

Diagnosis - Carbon monoxide

Carbon monoxide levels are usually caused by a rich fuel mixture, which can be caused by faulty air measurement, high fuel pressure or bad exhaust oxygen sensing. However it sometimes can be a result of poor air filter condition or on older cars of a need to adjust a carburetor.

Carbon monoxide is nearly always caused by too much fuel being consumed by the engine, which can be caused by a fault in the electronic engine management system, or with the carburettor on a older engine.

It can also be caused by a faulty injector, fuel pressure regulator or o2 (lambda) sensor.

High carbon monoxide or dioxide can be a killer, so while trying to diagnose these faults, it is really important to do so in a well ventilated area, as these gasses can be a silent killer with no odor or other side effects other than a headache and death!!

Carbon monoxide levels can also be high if the engine is cold, so make sure your engine is fully warmed up before you pay too much attention to the levels, and remember that it takes twice as long for the engine to be completely warmed up than it takes for the coolant to be up to temperature. This is because water absorbs heat much faster than aluminium, iron, steel or engine oil... so be patient.

Diagnosis - Oxygen

High levels of oxygen within the exhaust system can be an indication of poor exhaust sealing. But it can also be a sign of poor combustion, depending on what other exhaust gasses are present, it can indicate poor ignition, fuel system health or engine health.

It is also worth bearing in mind that if your exhaust system is not in good condition, air can be drawn into holes in an exhaust, just as much as a poor exhaust can blow its exhaust gasses out of gaps (a surprise to most people) which can cause elevated o2 levels in the exhaust gas.

The other problem with high o2 levels is that they can cause the o2 (lambda) sensor to see this air as a weak mixture, which in turn can cause the engine management system to add lots of excessive fuel to be added, which will show up as high carbon monoxide readings and possibly even high hydrocarbon levels. This means that if one of your emissions which seem high is the o2 level, please check the condition of your exhaust system and make sure that except for the tailpipe it is extremely air tight.

Good garages like JMG Porsche will use a smoke tester to test to see if the exhaust system is airtight (where it should be) as well as using diagnostic skill to find the cause of the high o2 levels and knowing what other elements may effect them.

Diagnosis - Drivability

Often a fault can manifest itself as poor drivability of the car. In these cases, exhaust gas analysis can assist in tracking down the fault.

Symptms and causes.

An important note to make before closing this article, is that there is a very large difference between symptoms and causes.

A good example might be an engine driving poorly, the exhaust emissions for carbon monoxide may be high and the engine management system may indicate that it believes the oxygen sensor is at fault. However both these items would be symptoms, even if when tested the oxygen sensor is found to be faulty. The actual cause may be something else, such as a mass airflow sensor providing a false reading of more air entering the engine than is actually happening. In this case the cause may have actually caused the oxygen sensor to become faulty, which will result in more than one faulty component, two in this case, one being a symptom, the other being the cause.

With this in mind, it is important to never assume the cause of a fault has been found, otherwise, as with the above example, the same fault will re-occur with a new component becoming faulty again. In all cases, even if a test shows a part to be faulty, further tests should be made to other components to be sure there are not other symtoms, faulty components and indeed one or more faulty components which are actually causes of the other symptoms.

It is therefore often important to allow your technician to perform multiple tests before and after a repair is made, it is often not the technician performing needless tests, but in fact ensuring that both the symptom and the causes have been eliminated, otherwise an expensive component may need to be changed more than once!


Finding dents is often easy as the dent is obvious.  However some minor dents are the kind of thing you only find when washing or waxing your pride and joy.

When buying your next Porsche, being able to find dents is often a good way to help negotiate a good price, but also helps you avoid buying a car which may have hundreds of tiny dents.

At JMG Porsche our detailing toolbox has for a long time included "The Dent Board": a simple printable document with parallel lines marked at variously spaced distances and thicknesses.  The board is the result of time and effort taken to find the correct patterns and spacing, thus when used correctly, will enbable you to find dents that would be difficult to find with the naked eye.  JMG Porsche have released this tool to Porsche buyers everywhere to help them find dents and even paint texture issues with ease.

So how does it work?

When looking into the paint of a car you will see reflections - often your brain will switch off noticing these reflections in day to day life.  You can, however, use these reflections to find irregularities in the paint or panel shape.

Unfortunately, usually the reflections are random and mask dents and paint defects.  However, with "The Dent Board" you can find them with ease because now the reflection is regular, straight and highly contrasting.

Simply download the pdf file at the bottom of this page called "The Dent Finder".  Print out this document and put it onto a clipboard or some stiff cardboard, we tend to laminate them as well because we use them everyday.

Then, whenever you are inspecting paint for texture issues such as orange peel or checking panels for dents, hold the dent board against the panel in a position so you can easily see its reflection and move over the panel keeping an eye on the reflection as you do so.

Even minor dents, orange peel textures or other undesirable blemishes on your Porsche bodywork will become instantly visible.

Variations of "The Dent Finder" are used by car detailers, paint specialists and bodyshops around the world.  Now you can also use our dent board or dent finder for free!

So, you're thinking of buying a Porsche? you may have already chosen the model for you, you may even have looked at some. What this article aims to provide is the background information and tips for buying a pre-loved Porsche.

We say Pre-Loved because that is the kind of Porsche you want to buy, it needs to have previous owners who have looked after the car well, one who's servicing is up to date, has been serviced by a specialist or a main dealer and one which is the very best example you can find.

What you want to avoid is one where the servicing has always been minor, performed perhaps by a normal all makes garage, that is less than perfect, has issues and is cheap. There is a well used expression that I in particular like to quote, which is "There is nothing quite as expensive as a cheap Porsche". This means that although you might get what seems to be a bargain, but often it will cost so much to repair, maintain and bring up to scratch, that you would have been better off buying the one you thought was overpriced but was in great condition, with a good history of maintenance and has obviously been loved.

Do not buy a fix-er-upper, unless you are doing it because you want to work on a car and restore it, more than you want to drive it. If you are buying one to fix up, you are probably better off buying some books on car repairs and restoration rather than reading these buyers guides.

So, buy the very best one you can find, and before you buy it, make sure that you have read not only this article, but also the one specific for the model you are buying, perhaps also print them out and take them with you when you view a Porsche.

One last word of warning before we begin. Ebay, be very careful of buying a car from ebay and do not look at the ebay prices and decided that those prices are what the cars are worth. Ebay is typically a car vendors (private or trade) last avenue to sell a difficult to sell car.

Lets start at the beginning, finding the car.

There are lots of places to find a Porsche for sale, you might see it parked on the side of the road, you might even see it advertised in a local paper or other publication that you read. Which is fine, but before you buy one, or even go looking, I would like to recommend some places to look.

Specialist and main dealer websites.

Yes it is a good idea to check out what we have at JMG Porsche, or what our customers are selling. But as an unbiased article, I need to also advise you look at what other reputable Porsche specialists have for sale. Henry at 911 Virgin always has good cars, as does Jonus at JZMachtech and the guys at Strasse in Leeds. Check out all these sources, what they have and use them as the yardstick as I know that they, like me, take a lot of pride in their cars and will stand by them if there is an issue.

There are also a new breed of Porsche specialists, who will often advertise in the Porsche publications but are not of the same school and level of experience, so sometimes you need to be careful which specialists you trust.


The independent Porsche Enthusiasts Club (Tipec) is exactly what it says in the name, visit their forum, put the word out that you are looking for the model you have chosen, and see what comes up. Its not often that a true enthusiast will sell their pride and joy, but when it does happen, its often a good car. But also the members in the forum may be able to help you with your search, as well as they may know of some of the cars you are looking at and what is wrong with them.


Porsche Club of Great Britain is much like TIPEC above, and also has some very helpful members.


Pistonheads is a great resource for buying a Porsche. Whatever model you are interested in, simply because it has such a selection being advertised by both traders and enthusiasts. Which is the important point, enthusiasts! A community like pistonheads is filled with enthusiasts, enthusiasts generally look after their cars, which are just the kind of cars you are looking for. Like anywhere though, you will notice that their are cars there that are advertised at a lower price, and some at a higher price. Always start looking at the highest price cars first, there is usually a reason why some are so much cheaper than the rest.


When selling a Porsche, a normal non enthusiast may advertise it via AutoTrader and it may not be listed in the forums or on Pistonheads. Although Pistonheads tends to have more Porsche examples than Autotrader, it is often worth taking a look to see what is around.

You have the short list

Once you have a list of cars to start looking at, things are going to get serious. There is the usual advice to call the people advertising as private vendors and say "I am calling about the car for sale", if the vendor says "Which car?" you know he is a trader and not a legitimate private sale. But everyone knows that, don't they?

When calling about cars, the important information to gather is....

  • Has the car got a service book? Is it showing a complete service history without gaps?
  • Does the car have any original MOT's over the years? (This can help prove mileage)
  • Does the car have any known issues? (Sometimes vendors will not tell you about any faults until you get there)
  • Are there any blemishes on the paintwork or any corrosion or damage?
  • Has the bodywork ever been repaired?
  • Is the interior in perfect condition?
  • Has it had any major jobs completed why they have owned the car?
  • How long has it been for sale and have many people viewed it?
  • How negotiable is the price (always ask this, after they have had to list any bad points!)
  • If so, how low would be their lowest price? (You will be able to go lower than this, even if they say it is the lowest price)

Once you have gathered this information, you will have a reasonable idea of how good or bad the car is, as well as a starting point for your negotiations after, and only after you have seen the car, test driven the car and have identified any additional issues with the car.

When you arrange a viewing, tell the vendor not to start the car that day before you get there, you need to make sure the car starts well and without smoke. Make sure the vendor is aware of this requirement.

Viewing the cars.

OK, so you are now going to look at some (hopefully) excellent examples of the Porsche model you are interested in. Take a pad and a Pen, so you can record details about the car and leave your humanity and love of your fellow human being, you are now a car buyer. Put on your best poker face and prepare to buy a car.

When viewing the cars there is one important piece of paper to take with you, a bodywork inspection card. There is an article on this website showing how to use one as well as how to make one. This is an important tool to find every single dent on a car, even the ones you usually only find after buying the car and washing it for the first time. Every dent you find can effectively devalue a car by £40, which is what many paintless dent removal companies will charge to remove a dent without breaking the paint.

Look for stone chips. I personally prefer to see some stone chips on the front of a Porsche I buy, it shows that the car has not recently been re-sprayed, which may be due to accident damage. You seriously would not believe how many Porsche for sale have recently suffered an accident.

The next job is to use our buyers guide specific for your intended model of Porsche, read the article before you view the car, but also read the article and follow its directions while you look around the car.

Chassis numbers.

Check the chassis numbers. Car's since the mid 90's have a chassis number in the windscreen. Older cars have them in various other locations. Check this matches the chassis number in the service book, on the log book, on the option sticker in the car, as well as other locations. The locations are also listed in the buyers guides specific for each model. But make sure they all match. If you end up interested in the car, you also need to check the chassis number matches the HPI report on the car, as well as the chassis number matches the specification of the car that has been advertised (read our chassis number reading guide) as you can learn a lot from the details hidden inside the chassis number. If all the details match, hopefully you are looking at a good honest car. If they do not, or they look like they have been tampered with, be cautious about the origin of the car.

Wheels and tyres.

Are the wheels fitted to the car the ones you would expect to have been fitted from the factory? If not, why not? and are the original wheels available? Many people want a Porsche with the original wheels, even if you are not bothered, the next owner might be.

Are the wheels damaged at all? Any curbing on the wheels is not only a sign the car has not been cared for as it should, but can also be a sign that the wheels have been structurally damaged. When viewing a car, make sure you point out any damage to the owner and negotiate the price accordingly.

When examining the wheels, check the tyres. How much tread do they have? Are they all the same make? How old are they (Tyres should be changed every five to six years, even if they have not worn out as they get hard and begin to crack after that amount of time. Missmatched tyres can be a sign of poor maintenance, especially if the two tyres on the same axel do not match, as tyres should be replaced at very least in pairs.

You also do not want to be test driving a car with poor tyres, bald tyres can cost the driver 3 penalty points and a fine for each defective one, a car with a bad set of tyres can cost you your licence!

Before the test drive.

Before you test drive the car, check the engine is cold to the touch. If it is warm, especially after telling the owner to not start the car that day, they might be trying to hide a fault with the car not starting easily when cold, a battery issue or even a puff of smoke as the engine starts, which could be a sign of a worn engine.

Check the engine bay for leaks, any leaks can be expensive to repair. A good engine bay will be dry of fluids other than the reservoirs that hold them.

If you see any fluid or damp patches, in the engine bay or under the car, here is a small rule of thumb for indentifying the cause.

  • Blue, green, pink or orange fluid with a consistancy of water, could be anti freeze.
  • Red or pink fluid with an oily touch, could be power steering fluid on pre 98 models, or transmission fluid on an automatic model.
  • Clear fluid is usually brake, clutch or in post 98 cars power steering fluid or sometimes automatic transmission fluid.
  • Black or golden fluid is typically engine oil or transmission oil in manual cars. Transmission fluid often smells bad, a little like cat pee (if you know what that smells like)

So there are no leaks? What else to check? Pull off the engine oil filler cap, look on the underside of it, as well as bellow it. Look for any signs of a thick creamy substance that has a coffee colour, any sign of this can be an early sign of head gasket problems. Although it can be a sign that the car has not been driven often and moisture is building up inside the engine, possibly still not a good sign and may require professional inspection.

Next you should pull off the coolant cap, is there any dry signs of evaporated coolant around it on the header tank or on the cap? It could be a sign that the cap is either faulty or the cooling system is building up too much pressure. In any case, its not a great sign and may require professional testing.

Lastly, check the brake and clutch fluid levels, they should be between the minimum and maximum level.

You can start the engine.

Any Porsche should start without the need to tickle the throttle. Make sure the car is not in gear, the handbrake is fully applied and that the drivers window is wound down. If it is a newer model, you may need to depress the clutch or press the brake peddle while you start the car, this can be normal if the vendor says you need to do it.

Once the car starts, get out of the car and look at the exhaust, there should be no blue smoke, if it is cold there should maybe be a small amount of visible white water vapor, but no smoke as such.

After observing the car running for a few minutes, you can proceed with the test drive.

The test drive.

You need to take the car for a reasonably long test drive, at least 30 miles. This should include stop-start town driving, country lanes as well as motorway cruising.

During the test drive the car should be taken very close to the rev limit on acceleration at least a few times, occasionally checking the mirrors for signs of smoke, which if blue, can be a sign of engine wear.

Also during the test drive it is important to at least once hold the car in gear at high rpm, let off of the throttle and coast to a lower rpm under engine braking and then accellorate hard. If you get a puff of blue smoke seen in the rear view mirror, it could be a sign that the valve guides are worn and require a top end rebuild.

The rest of the test drive should be spent listening to the engine note, searching for squeeks, rattles, vibrations or knocking noises which seem to be abnormal. They could be an issue with the suspension, engine, transmission or trim, but if you experience any, it will be best to ask whoever you get to perform a pre purchase inspection (PPI) to look into these.

If at close to 40 mph a rhythmic, deep humming noise can be heard, this is often a sign of wheel bearing issues.

It is during the test drive that you will reap dividends in experience from test driving more than one car. You will become familiar with what is normal, what is a quirk of the model, as well as what is most definitely not normal.

All Porsche models should have a relatively easy gear change (some older 911's may have a slight awkwardness) and a reasonably light clutch, in particular the later Porsche models after 1988 should have a clutch which is no heavier than a normal domestic car.

While in the cockpit, check the odometer digits are straight, sometimes (but not always) the digits not being level can be a sign that the mileage has been tampered with. Check the rest of the interior seems to match the same mileage. A car with only 30,000 miles shown, should not have a worn out gear knob, steering wheel and pedal rubbers!

Likewise a very low mileage car should not have worn out seat bolsters or carpet.

Once back after the test drive, I recommend you leave the engine running for at least 10 minutes while you make some last checks. You need to be sure that the engine does not overheat, the oil warning lights do not illuminate (except for some very early 911 models) and that the exhaust is not blowing. Also, once you switch the engine off, watch the car for 10 minutes to make sure the car does not begin to leak coolant or oil.

Now the test drive is over, it is time to check the paperwork.

The service record should have a stamp for each service, often with ticks or notes to say which service was performed. Look for the mileage not being sequentially rising after each service, it would not be the first time that I have seen the mileage of a car go down in one year, which can be a sign that the mileage has been tampered with.

If there are old MOT's in the paperwork, check through them and make sure they mileage ties in with the service history, you are asking the vendor to be patient while you check the paperwork, so it is worth thanking him before you start and explain that you are checking everything is in order. Most honest vendors will have no problem with this.

In an ideal world, there will be stacks of receipts with the car. However, if the car has been owned by a business at some point, there is a chance that the receipts are not with the car because they have been archived as evidence of the business accounts. So do not be too alarmed, as long as there is some record of servicing, even if it is just the book. If there is a pile of receipts, it is a bonus.


If you are interested in the car, but want to try some more, it is worth telling the vendor this and negotiating the price. It is worth trying a low offer, perhaps 60% of the price you know they will accept. This may seem harsh, but sometimes a vendor is desperate to sell, so you may get a bargain, if not, at least you have started at a good point to negotiate upwards, as the vendor negotiates downwards. But if you are interested in driving more, please do, even if the negotiated price is good. It will still be good tomorrow, even if the vendor says the price is if you buy it right now, ask yourself why would it change to a higher price tomorrow? Don't fall for this.

Before you pay any money for a Porsche, I would recommend a pre purchase inspection by a recognised Porsche specialist, yes it costs money, but so does buying the car and a professional pair of eyes can often save you a fortune or at least give you some ammunition to negotiate the price downwards further. I would also recommend you have a HPI report produced for the car to ensure it has no finance outstanding, is not stolen and has not been a total loss or a category A, B, C or D. Cat C and D should not be an issue if there is a valid reason, it is quite normal after an accident for an owner to refuse a repair from an insurance company if they are not prepared to pay for a authorized Porsche repairer, or Porsche specialist to make the repairs, which can result in the insurance company to list the car as not inspected, which can result in a cat-C or cat-D marker being placed on the HPI history, some investigation may be required to find the reason, and the car should be discounted by up to 25% to reflect this.

My main advice in closing would be to recommend the following.

  • DO NOT buy the first example you see or test drive.
  • DO NOT be soft on the vendor just because he is another human being.
  • DO NOT trust the vendor just because they are a business.
  • DO thoroughly check every car you consider.
  • DO have a pre purchase inspection performed by a Porsche specialist on any car you consider.
  • DO pay for a HPI check on any car you consider.

Happy Porsche buying and remember, please read the buyers guide for the model of Porsche you are interested in.

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