Misfiring cylinder 5.
 

Hey guys.

So I was out on a drive in the 986 recently, as I was pulling up to my drive way my check engine light started flashing I pulled the car into my garage turned it off and scanned on my OBD2.

P0305 (misfire on cylinder 5) I came on the forums and researched what it could be. Most of the answers given said to replace coil packs and spark plugs. I then up the car on jack stands and changed my spark plugs and coils all around.

Problem is still there, i'll turn the car on and the same code comes back. I tried disconnecting my MAF to allow the engine to run without the MAF's assistance and it made no difference. I then checked my coolant and there's no oil in it. My car only has 56250 Miles.

Has anyone had similar problems?

Thanks, Lucas.

could be wiring to coil pack. perhaps check for mechanical damage to wire harness?

Checked, and no damage!

This is a tough one. I'm worried that the ECU fuel trims might be maxed out and even with the MAF disconnected this still causes the P0305 code. Try testing the MAF again by clearing the ECU first;

Disconnect the battery to completely clear the learned ECU fuel trim settings.
Disconnect the MAF.
Drive it and check the codes. You are sure to get a CEL for the MAF being disconnected, but we want to see if the P0305 returns.

If P0305 returns, then the MAF is ok and you're back to a problem that seems to affect only Cyl 5. If no P0305, its the MAF. Clean MAF, clear ECU, and monitor.

I don't think its the ECU nor the MAF. The CEL is flashing i'm worried it could be something major like a cracked head but then I think my car has 565XX Miles?

First, you need to get the car scanned on a Porsche specific system (PST II/PIWIS/Durametric), as some generic OBDII unit give erroneous results.

Second, any of the Porsche systems can look at air/fuel ratios, individual injectors, etc. to eliminate them. Third, if you think there is a serious mechanical issue with cylinder 5, get that cylinder leak down tested (you could have a dying or dead valve spring, etc.).

Yeah we did a compression test on the cylinder and found the culprit. Crack in the cylinder wall of cylinder 5. :(
Now, to rebuild it...

CR