F6C

Have a misfiring 987.2 3.4 Cayman that is proving problematic.

Initial symptoms were a a sudden solid CEL, but at this stage did not notice any rough running. Pulled codes and got misfires on all six cylinders. No other engine codes. I'd also noticed some smokey cold starts. So, AOS replaced with a new one and the MAF swapped out for a used one that is thought to be good but not known absolutely for sure.

AOS was done first. Starting up after that was fitted had the car running very rough, which is hadn't before. Unplugged the MAF and running seemed to be improved. So fitted spare used MAF that was at hand.

Initially, seemed to have fixed the problem, but after 30 minutes driving, flashing CEL and rough running. Restarting cleared the light momentarily and the rough running was gone, but CEL quickly came back. Codes same as before. Misfires on all cylinders.

I will get a new MAF in to exclude that and clean up the intake, look for oil etc. What are my other suspects? Soiled plugs from possible failing AOS? The fault seems a bit binary / on-off for that. Vacuum leak? Cam sensors?

Thanks

KrisA

I'd start with the plugs. If the AOS failed and there was lots of oil going into the intake the plugs could be fouled.

badabing

If you are pulling the coil packs to change the plugs I'd replace them too unless they are fairly new.

They are a common failure point. About $50 each from the online Porsche dealer part discounters.

F6C

Yes, thanks, coil packs worth doing, but doubt they are the reason the car is suddenly throwing misfires on all six cylinders...

badabing

I wouldn't be too sure. Coil packs are the reason some people experience problems with the pdk. Coil packs are the reason some people get coolant system warnings on the dash.

When they go bad, it causes havoc with the whole electrical system.

F6C

Well, the MAF has been changed for a new one, new inlet valve actuators on both banks, cleaned out some of the inlet. It's been run for a while with no CEL, but looking at the live data, it's still misfiring quite a bit, more than it should be. Again, this is misfires on all cylinders.

List of possibilities I can think of:

Coil packs
Crank sensor
Knackered flywheel causing problems with crank sensor?
Vacuum leak (this has been checked for up to a point, perhaps not exhaustively)
Outlet valve actuators
Electrical fault of some kind?
Coked up / dirty inlet valves / valve seats

Thoughts, anyone?

F6C

Oh, plugs inspected and deemed very clean.

hueyhoolihan

sounds like you fixed the original CEL problem. what are the misfire numbers?

F6C

I wouldn’t really say so. Original problem
was CEL due to misfires on all cylinders. It’s still misfiring on all cylinders. Ok , it didn’t throw a CEL the last time I drove it, but the live data was still showing lots of misfires.

KrisA

I'm far from an expert here, but if this was my car I'd just throw a complete new set of coil packs at it and see what happens.

F6C

It's not impossible, but I really doubt it coil packs. I've had coil pack issues in the past and this is only superficially similar.

There's no way they're all gone and I doubt a given bad coil pack would be bad enough throw the others out while also not being bad enough to trigger CEL most of the time. It's currently a sort of low level misfired on all cylinders that hasn't triggered a CEL in the last three hours of driving, but you can see the misfires racking up in the live data.