07 350z

As the title suggests I have a misfire at idle.

I actually have a new engine. My buddy and I swapped engines. Long story. I'll throw up some pics though just for fun.

Anyways, engine runs great. Except it misfires at idles every once in a while and then throws a code.

I just swapped out the coils and plugs. If anything, now it is worse. These are NGK plugs and HITACHI coils off of the old engine so I know they are good.

Also, we swapped manifolds, fuel rails, and injectors. So I know all of that is good and isn't my issue.

I just smoke tested the intake and that came back negative. I smoked it for a good half an hour with a real smoke machine. Nada, nothing, not even a wisp of smoke came out anywhere.

I'm about out of ideas except for an idle relearn. Not sure that's going to do anything but it's something to try. Other thing I could try is cam position sensors. My buddy ran this engine for 15k miles without a hiccup so I'm not sure what the issue could be. It is a JDM engine but we swapped harnesses, intakes, fuel rails, and all the accessories.

If you have an idea please let me know.

Thanks,
Braden

 

Could be a cam or crank sensor, but it's weird that the problem is intermittent. Usually if a sensor goes bad, it's a constant problem, always present.

Is it a random misfire code? Or is it giving you a specific cylinder?

If it's a specific cylinder, I would do some wire harness continuity and short checks (focus on coil pack plugs and injectors for that cylinder). Perhaps some of the wiring got compromised during the swap. A single pin on a plug could be loose or some shielding got nipped and might be shorting out intermittently.

If it's random, then I would check continuity for the cam and crank sensors. Worst case scenario and highly unlikely, but the driver(s) for the coil packs in the ECM could be failing.

Last idea I got is potential fuel injector issue, I know you said you swapped them, does that mean swapped with brand new? Are they OEM or aftermarket? Is there a chance one of the injector seals is leaking or losing pressure?

Good Luck!
-Icer

 

It's multiple misfire. It did show cylinder 5 and 3. Next time the code came up it was cylinder 3.

Since then no code but I can feel it sometimes at idle.

I had the same thoughts about a sensor. Sometimes they can soft fail and cause issues. Not all the way dead but somewhat defective.

It is very possible some wire or pin got a little messed up but one would think that would cause issues going over Chicago potholes, not sitting completely still at the stop light.

I might just replace the cam sensors for good measure. Can't hurt. That was my next thought.

I haven't heard of the ECM causing this but I won't rule it out.

The I ejector are from my old engine. They are a flow matched set of OEM injectors. They were flow matched 2 years so I'd think they'd be pretty clean but also, couldn't hurt to send them in for cleaning for good measure.

I did send logs to my tuner. I couldn't get it to misfire though. He says the logs look great. It seems to only do it during warm up, not at operating temperature. It's very possible it just the tolerances on the lightweight rods and pistons causing race car problems when the engine is cold. Ttis is definitely a thing and might be something I now have to live with. I could have the tuner raise my reline to 1k or maybe 1200. Might fix the issue. There's a reason race cars idle at like 2k