Porsche Enthusiasts Club Forum

'Ello peeps. Can anyone tell me (in brief) what coil packs are and how important it is (or not) to have cracked ones replaced? Cheers

sounds like a potential issue, going forward, advice will , I am sure be forthcoming soon

On your engine you have six coil packs, one for each cylinder.

What they do is convert an electronic signal from the engine management computer into a big spark to ignite the fuel and air mix.

Back in the old days, you used to have one coil doing the same kind of job (making a spark) and a distributor cap and rotor arm to direct that spark to the right cylinder that needed it, and plug leads to connect all these things up.

Then, someone, somewhere decided it was a good idea to make one coil for each cylinder and do away with the distributor cap, rotor arm and plug leads in the name of reliability and to a very tiny extent improving fuel economy, emissions and performance.

The Boxster, Cayman, 996, 997, 991, Panamera and Cayenne all have this technology, as do many modern cars.

However, on the Boxster, Cayman, 996, 997 and 991 (all the models with a flat engine) have these coil packs exposed on the underside of the car, which causes the metal within them to corrode, expanding the plastic casings until they crack.

Once they crack, water manages to get inside them, which eventually causes missfires, loss of performance, loss of ecconomy, loss of reliability and eventually loss of a working car.

In addition, once they start misfiring, which may not be noticed by the driver, high hydrocarbons (unburnt fuel) then contaminates the sensors in the exhaust, the catalytic converter.

Also, the misfires themselves can cause damage to the engine if a car is continued to be used over time.

The Panamera, Cayenne and most modern cars, the coil packs are on top of the engine, not exposed to the elements, so less frequently corrode and crack, which means they tend to be less trouble.

On some models, changing the coil packs can be a chore and time consuming. Double jointed wrists and a wide selection of tools are handy.

We change them quite often, but this does not mean they are a particular problem point for the flat engine Porsches, they often last anything from 5 years to 10 years, it all depends how often the car is driven in the wet, how old they are and it is possible that driving style (and how quickly they warm up and cool down) may also contribute to failure.

In a nutshell, your coil packs are used to convert (or transform) the low 12v battery energy into high voltage (30000v plus) bursts of energy for your spark plugs. It it this high volt burst of energy that actually jumps across the air gap of your spark plug to ignite the air/fuel mixture in your cylinders.

If the coil packs are cracked or broken, then the insulative properties of the coils are seriously compromised and you run the risk of the high voltage burst of energy finding an easier electrical route down to earth (or the negative terminal of the battery). This is exactly what causes a misfire. Instead of sparking across the air gap of the spark plug, the electrical energy will find an easier route to ground by breaking down the coil insulator and completing the electrical circuit to ground via some other undesired means.

Once you've had one misfire, then you will subsequently get more and more misfires and it will happen more and more often. This is because the electrical energy that passes through the coil insulator essentially burns a conductive track through the insulator. As more and more misfires occur, the track becomes more and more conductive making it easier and easier for the electrical energy to pass through. This diverts the desired spark away from the spark plug more and more often and under more and more engine operating conditions.

In short, everytime you have a misfire, you put your catalyst under undesirable operating condition. If there isn't a spark in the cylinder, the air fuel mixture doesn't combust correctly and the incompletely burnt mixture enters the exhaust system and the catalyst. This elevates the exhaust and catalyst temperatures and can and will lead to permanent catalyst damage and failure of your vehicles's emission control system (the emisions warning lamp in the car will illuminate).

I hope this helps. It isn't meant to alarm you. Get in touch via a PM if you need further clarification, I'm happy to help and advise further.

Wow, thanks guys (Jon / Max)!! That's brilliant - they said that TIPEC was a good place to be. Sounds like I need to get these replaced at some point soon and now I've got a good idea as to what they are / do to boot. I knew I'd learn something about cars one day hehe. Thanks again!!!!!!!!!!!!!!!!!!!!!

What great answers thanks.