TL;DR: Intermittent P0300 Class A misfires. No limp mode, no power loss, no stumbling, no smoke. Plugs, coils, vacuum leaks, PCV, MAFs, and cats ruled out.

2008 G37S Coupe 6MT. 76xxx miles. Ark Catback. FI RHFC(P0300 predates them).
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Hi all-

I've been hunting down an intermittent P0300 Class A (MIL blinking) misfire code for a few weeks, and I'm running out of ideas. Hoping someone here has some suggestions.

The misfires tend to occur on a warmed engine during light load(normal driving 2-3k RPMs) or at idle. I don't feel any loss in power or any stumbling in the car's acceleration. I've been monitoring OBD data and the ST fuel trims on Bank 1 go into the high positives during misfire events. I've fueled up at several different gas stations throughout all of this.

I've had the dealer look at it, they diagnosed it with leaky valve covers and clogged cats. I've replaced both and the problem persists.

So far I've:
-Replaced valve cover gaskets (dealer's idea)
-Replaced cats (dealer's idea)
-Replaced battery
-Replaced PCV valves
-Cleaned throttle bodies
-Cleaned MAF sensors
-Checked for vacuum leaks
-Ran a bottle of Techron through
-Swapped coils between B1 and B2
-Swapped MAFs between B1 and B2
-Replaced intake filters
-Replaced spark plugs


This is what fuel trims look like during Class A misfire events(MIL blinking):
......STFT B1...STFT B2
1...+16.4........-6.2
2...+17.2........-4.7
3...+14.1........-6.2
4...+25.0........-0.8
*swapped coils between B1 and B2*
5...+24.2........-5.8
*swapped MAFs between B1 and B2*
6...+15.6........+4.7

I'm going to look at injectors next, but I feel that they would have thrown a cylinder specific code if that were the case.

Thanks

 

Check oil pressure at idle and under load. If it's low, it's rear timing cover gasket failure.

 

I've actually come across several of your old posts on this issue through the course of my research. I've spent the last couple of days getting quotes on parts and labor for this possibility.

I'm getting my oil pressure tested on Wednesday.

I'm kind of hoping that it is this issue (so I can get rid of this ticking cardboard timebomb) and also hoping that it's not.

Thanks for the info, both now and past.

 

Have you resolved the problem yet? Once it started to get cold out my code has been popping up about once or twice a month. I've been putting it off and just starting to look at fixing it.

 

It would help to know the logic behind the codes so to know what to look for. If only there was someone at Nissan (Nashville or anywhere) who was sympathetic to our cause that could help with this stuff.

Is there an answer or have you tried other VQ forums?