porsche_fan

Recently the CEL has been lighting up fairly often in my car and the fault codes always read as a misfire -- sometimes it's all cylinders, sometimes it's just 3 or 4.

I have read a lot in the archived posts which discuss the misfire codes actually being caused by the flywheel. I also have the main symptom of a bad flywheel that I have seen posted -- the engine chatters/wobbles when it is turned off (are there any other symptoms to be looking for?).

I have started working through the main ignition parts; I have replaced the spark plugs and will be changing the distributor caps next, but I have a feeling that the main issue will end up being the flywheel.

My question is: if the flywheel is the problem, how urgent is it to change it? Could you cause damage by postponing this fix? Once it is replaced, will the engine feel smoother?

Any advice or experience with the matter is greatly appreciated.

The car has approx. 54K miles.

Mike J

If its the flywheel it should be good for quite a while - the inside piece is rattling/loose and is causing the crankshaft to slightly vary in speed, which the computer picks up as a misfire. Its not going to fly apart, and if you are getting a good rattle when you shut it off, that is definitely evidence.

You have done the usual stuff, like making sure that your belts are truly Porsche OEM?

Does the car feel smooth or is it a bit rough on idle, etc?

Cheers,

Mike

hkate

Porsche oem belts are a must. I had misfire w continental. Porsche belts cured it.

Kika

Have you checked your plug wires? They can get cracked and cause misfires also.

Steve Weiner-Rennsport Systems

+++! I find these to be a big offender since they are rarely replaced on time.

dp2boy

Not to hijack, but are the plug wires a pretty simple DIY or is it a bit more involved ?

Quadcammer

plug wires blow on NA cars unless the previous mechanic made a few little helpful changes

porsche_fan

Thank you for the responses.

The idle is smooth when I first start the car, but after the engine gets hot (particularly after stop and go driving), the idle is far less smooth -- the engine feels almost "lumpy".

From what belts I can easily see, they all appear to be OEM belts.


I think I will be headed to the spark plug wires after the distributor caps. By the way, what is the recommended service life for the spark plug wires? While changing the plugs, I did not notice any cracked wires, but they were certainly starting to show their age.

Slow Guy

Plug wires aren't difficult, just "challenging". If doing the job with the engine in the car it helps to have long, skinny arms (an extra elbow joint would help too).

The most common time to notice bad plug wires is starting the car when the weather is extreemly damp/wet as this is when the voltage in the bad wire will jump to the surrounding metal (sometimes you can even see it).

Quadcammer

eh, you ask me, taking out those philips head screws holding the plug blocks under the intake with about a quarter inch of clearance is a major *** pain, but thats just me. or of course removing the intake to avoid doing so.

Slow Guy

I have a couple of mini-ratchets with phillips bits that work well.

Kika

the 4-6 lower plug wires get exposed to a lot of heat, and from what I have read, those tend to dry out soonest.
you can save some money by purchasing the wire kits and re-using the connectors, assuming they are still good.

new full 993 wire set isn't cheap.

mgianzero

Hey Mike, I'm also getting a random misfire (just as above poster) sometimes different cylinders. I changed the belts (all Porsche OEM) and checked their tensions with Porsche tool, and changed out all spark plug wires with Beru OEM. Car also runs a bit rougher once it warms up. Maybe has a small rattle when I shut her down or start her up but I'm not sure if there's really a rattle or if that's just in my head? What's it really sound like? Anyone have a recording of it?

techman1

Wondering if the dual mass flywheel is affected by heat, allowing one that is "On its way out" to act up resulting in idle and CEL problems?

mgianzero

That's a possibility I guess. I also changed out my idler valve (brand new) and didn't make a bit of difference.

Any one else have any thoughts?