Big Jimbo

For about the past 6 months my 2012 P30 with 31K miles, bone stock, never re-flashed, has had an occasional engine misfire (Usually #7) that will start after the engine is warm and continue until I turn off the motor and immediately restart it and then it runs perfectly for the rest of the trip. I have tried everything I could find on this forum. I have replaced the plugs, had the fuel injector cleaned and flow tested, and replace all of the O2 sensors. I don't see how it could be a mechanical issue like an intake leak because I don't think it would then run normally after turning the engine off for 1 second. To me that seems to indicate an electrical problem. It will run perfectly for days and even ran a 12.6 sec at the local strip with 91 octane and it was 104 degrees out! Yesterday it started missing much worse with many cylinders and even killed while idling. I went home, restarted it, and now all perfect again. I have an iSoft MBII scanner and it gave codes for misfire of 2,3,4,6,and 7, and also "actuation of ignition coil 7 has an electrical fault or open circuit." I did the lambda O2 sensor testing and everything looks ok on all the data streaming on the scanner. I am totally out of ideas. Could it be my ECU is going bad? I was planning on installing a supercharger but want to get this fixed first! Thanks for your help!

roadkillrob

Seems like you have replaced all the likely suspects, did you replace the coil for cylinder 7? If not I would switch 7 with something else an see if the misfire moves with the coil, that seems like the only component you have not replaced.

Big Jimbo

Thanks, I did replace the coil for #7 early on and still got the error on #7 yesterday.

bhamg

I would replace - not just reseat - the fuse or fuses for the module(s) that control the injectors.

Big Jimbo

I will check that out today, thanks for that excellent suggestion. I am also going to check the ground points I can find for the engine and harness. Will update with results.

INS1GNIA

Take it to the dealer (if you haven't) and see what they suggest. Not saying to get the work done there, just to see if they can come up with anything out of the norm.

Big Jimbo

Follow-up note
I can't thank you enough for your suggestions! After about two weeks with no misfires I am cautiously declaring victory. I removed the engine related fuses and relays in the engine fuse box and carefully inspected them, put a light layer of dielectric grease on the contacts and reinserted them. I didn't actually replace them but checked with a resistance meter for any flaws. I also removed the wires from the 4 ground pegs in the engine compartment and cleaned them and applied a light layer of dielectric grease. I then unplugged the ECU harnesses for inspection and cleaning. I am not sure which one of those procedure fixed the problem, but this somehow released the German gremlin hiding in my electrical system. Thanks again!

Racin_fool

Sometimes that is all it takes.. Re-seating a fuse, relay or control module, cleaning a ground point and terminal, adding some corrosion/arcing protection.. Doesn't always have to be expensive to fix these cars.

bhamg

Awesome, good to hear.