I've had an intermittent cylinder 4 misfire since installing my BP kit and UpRev tune.

This is EXTREMELY intermittent which has made it difficult to troubleshoot.

I've gone 10+ drives with hundreds of kilometers and not had a single misfire, car runs like a top. Other times it will misfire from start up and keep misfiring while driving for 10-15 minutes straight. Conditions make no difference, cold start, at idle, cruising on the highway, warm or cold air temps. Nothing seems to make it start or make it go away. It's maybe slightly influenced by load, if it starts and I slowly give it some more throttle it seems to get better but will either return immediately off the the throttle (or not, it goes away on its own too so I might be crazy thinking its related).

I have checked and changed (either new or swapped from another cylinder) all of the following parts with no difference:
- spark plugs
- coil packs
- injectors
- ECU
- MAF (UpRev GT)

I just changed the ECU tonight and that was my hail mary play but test driving around got the misfire going. I happened to be data logging at the time and was able to get the misfire on 2 logs which I've attached here.

If anyone has any ideas at all on what could be causing this I'd be thrilled to hear them.

 

So the miss doesnt follow when you change the coil packs to difference cylinders?

You put in brand new plugs (looks dont mattter, use brand new) and gapped to at least 0.030" or smaller?

who did your tune? AFR are spot on? whats your fuel trims?

Do you have a wire tuck?

have you swapped your MAF?

 

No, doesn't follow coil packs.

Brand new plugs have been put in multiple times gapped at .032.

Seb from SpecialtyZ is the tuner. Idle AFR is 14.5-14.7 unless its misfiring then its hunting all over the place. Cruising around AFR is steady unless there is a misfire. Having an issue with stuttering when hitting the pedal hard to go to WOT that we are working on right now. Spikes lean at first and then settles in too rich.

No wire tuck.

Forgot to mention the MAF. I have an UpRev GT MAF and swapping it for a new one didn't change anything. Others have noted my MAF voltage seems to be high for a GT MAF. Attaching 2 WOT logs from right after I changed the ECU last night and before the misfiring started.

 

Try switching an injector-NVM I see you did that. Missed it first read over.

Any chance that cylinder has low compression or a head gasket leak?

 

Compression and leakdown tests were performed. No issues.

Also keep in mind when it isn't misfiring, it is running *perfect*. It goes from running smooth as silk to clattering like a jalopy and back again.

A head gasket leak should be getting worse or leaking consistently enough for the misfire to occur regularly or under certain temp conditions but it is completely erratic.

 

crank sensor?

 

It sounds like most crank sensor issues throw a crank sensor code, create hard starting issues and very poor engine performance.

My symptoms are quite a bit different and I've never thrown a code for any sensors.

I was hoping to get to a point where there is some logical troubleshooting to do but it looks like my destiny is to replace sensors and parts and hope to eventually find the cause through trial and error. Damn.

 

is that injector pulse value in ms with or without injector latency added to it? Some injectors have latencies over 1ms. I would imagine getting that close to the latency value could cause some fueling issues.

Maybe have your tuner reflash the car back to stock and drive around like that...low load. Stick stock injectors/maf back in. See if the misfire goes away.

https://my350z.com/forum/forced-indu...injectors.html

 

and you didnt change your clutch recently either right?

 

Just curious what makes you say it is limited to cylinder 4? I'm not sure if I missed that. Sometimes when the first hit of missfire happens, the car will read lean then rich. I've seen that be the result of mechanical damage twice now...

What about cam sensors? One might be going bad... Idk sounds like a sensor issue of some kind

 

Sold my stock injectors so I'd have to buy some to go back to a stock tune but still not a bad idea.

Clutch hasn't been changed recently, was upgraded well before the turbo was installed.

It is limited to cylinder 4 because the only code I get is P0304 and I've used the cylinder power test in the UpRev software to confirm that only cylinder 4 was missing.

Every issue I've read about with cam sensors they always throw the code for cam sensors. I may end up replacing sensors one at a time anyway if we don't find anything in the tune.

 

Assuming it's not a mechanical issue -- Get a scope and check the signals to cyl 4 (injector and coil pack) and if the signal is weak/missing during the misfire test again at the ECM itself. Double check power and ground on the coil/injector if the signal appears good on both ends. If the signal is good at the ECM, trace it from the coil/injector all the way back to the ECM. There's a couple of connectors and a BCM along the way.

 

You pay for shipping and I can let you use some stock injectors.

 

Misfire has been resolved.

It ended up being internal damage to the plug that clips onto the cylinder 4 injector.