2009 451 Cabriolet P0302 Misfire

[chrisroug]

Hi Everyone!
My name is Chris from California. I just purchased a new to me 2009 451 Cabriolet. I bought it knowing it had a misfire, and assumed it needed valves. Much to my surprise the compression was 155+ in all 3.

As for troubleshooting I have moved the coils around to different cylinders, the spark plugs to different cylinders, and the injectors. No matter what I do the issue stays on cylinder number two. I checked the grounds down by the battery and back by the ECU. I ohmed out the wires for coil pack 2 back the ECU and they're all good.

The thing that I find interesting is it will run fine for about a mile or two then it will throw the code and begin misfiring an idling rough. If I turn the car off and restart it it immediately runs well until it happens again after another mile or two. I did let it idle for about 15 minutes issue free, then I went to test drive and it happened again.

I appreciate any help on this, it's really got me stumped.

[Thrumbleux]

It's the earlier 450 with the Suprex engine that burns exhaust valves.
Given you've checked ignition components - swap fuel injectors cyl to cyl?

[chrisroug]

It's the earlier 450 with the Suprex engine that burns exhaust valves.
Given you've checked ignition components - swap fuel injectors cyl to cyl?

Thanks for the reply, that has been done. Today I want to look at the crank position sensor, since this is what triggers the coils.

[Thrumbleux]

Sorry - missed that you'd swapped over injectors too.
Symptoms of a failing CPS are usually the engine quitting when hot and idling and restarting after a period of cool down. What code is being thrown up? Is it just a misfire on #2 cyl? If not, how do you know it's #2 cylinder missing?

[chrisroug]

Only code is P0302 is the only code. it's so odd right as it misfires if I shut it off and fire back it's fine. I also did a hot compression test today and it was 155 across all 3 cylinders

[Thrumbleux]

Tricky one this!
Good compression across all cylinders - but could #2 have an occasionally sticky valve? Running out of ideas here!