The other day I was driving and started to notice a tap from the engine and car running rough. I got home and scanned it and have a p0300 and a p0306. The misfire counter on cylinder 6 is bad with residual misfires on cylinder 4 and 5 as well but not too bad. I have replaced the plugs, swapped coils and injectors, replaced fuel dampers, replaced valve cover gaskets as well as the lower and upper intake gaskets. I have ran a gas treatment through incase it was bad gas and also did an oil change with ester oil. Also have cleaned the mass airflow sensors and throttle bodies but I am still getting a bad misfire from cylinder 6 that even causes the CEL to flash. I am going to be doing a compression test on it this weekend to test that but does anyone else have any ideas what it may be? It's a 2012 G37x with 104k on it. Any help would be appreciated. Thank you. 

Bump

See that it isn't a blown head gasket before you spend another $ 1000 . The old "exhaust in the coolant " check .Test pellets that change color , if exhaust present, when dropped in a sample of coolant sucked out of radiator .
And that's not the only test , just sayin. Like compresshun etc. etc,.

If all coils are functioning properly (verify good spark at all 6), I'd bust out the multimeter and start checking grounds AND ohming out all six injectors.

Common issue on the G35 and G37. What's the plug look like in 6?

AZhitman wrote: ↑

Fri Aug 14, 2020 10:23 pm

If all coils are functioning properly (verify good spark at all 6), I'd bust out the multimeter and start checking grounds AND ohming out all six injectors.

Common issue on the G35 and G37. What's the plug look like in 6?

I put brand new plugs in it. After running it for awhile I pulled the plugs out to check carbon tracing on it to make sure they were all igniting properly. When I pulled the spark plug on cylinder 6 after only about 10 minutes of running the spark plug in cylinder 6 was completely black with high heat brown spots on it. None of the other plugs looked that way. It is almost like cylinder 6 is having preignition but I can't narrow down whats causing it.

ChrisDix83 wrote: ↑

Sun Aug 16, 2020 8:28 am

I can't narrow down whats causing it.

Any update? I'm having random misfires and flashing CEL.

All the best,
~HollywoodJackson~

ChrisDix83 wrote: ↑

Sun Aug 16, 2020 8:28 am

I put brand new plugs in it. After running it for awhile I pulled the plugs out to check carbon tracing on it to make sure they were all igniting properly. When I pulled the spark plug on cylinder 6 after only about 10 minutes of running the spark plug in cylinder 6 was completely black with high heat brown spots on it. None of the other plugs looked that way. It is almost like cylinder 6 is having preignition but I can't narrow down whats causing it.

Have you de-carboned it?