S14 heavy stutter/running rich/misfire? Vid inside

[sqd]

Well, I'll start off with a very quick introduction - name's Robert, 23 year old guy form Sweden, been reading on this board for a few weeks now, but I just signed up since I figured you nice people might be able to help me, trying to get as many people I can to add some input.

And right now, my car is having some sort of engine-related problem, when i start to reach about 4000 rpm, the car starts so stutter quite violently, like it's running rich and misfiring. I can almost pull it to redline if I really push it, but the car really needs to struggle for that to happen.

This just happened for no reason about three days ago. First I reset the ECU by disconnecting the battery for a while, then it went back to normal for about 30 minutes, and now that does not fix the issue.

Checked for boost leaks, found nothing unusual, I had a tiny leak but I fixed that (couldn't have been big enough anyway, I think), and no difference. Replaced the plugs, gapped to .03 (the previous plugs were gapped to .027) and no difference. When i pull the MAF, the car won't even idle. So yesterday i pulled the O2 sensor, and it ran noticeably better, i could pull it to redline on atleast the second and third gear, getting full boost and so on. It still sputters and acts all uneven in the mid-rpms, but a lot better at high rpms/boost. So not perfect, but better.

So me and a friend filmed this clip when i drove it, it starts at 6 minutes since everything before that is just in swedish and non-related :)
(This is before I unplugged the O2 sensor)
YouTube - 200sx Problem (http://www.youtube.com/watch?v=GTvRI_fDW28#t=6m)

Oh and at the beginning, when im holding up the PFC, i rev in neutral, and it runs badly even then.

Just listen and keep you eye on the yellow/orange display in the lower part of the video, that's the AFR value (i only have a narrow-band right now). When i apply throttle, it goes down to 10 at a few points, so im definately running rich.

A short list of relevant parts so you know what's on the car:
- Wiseco pistons
- Eagle rods
- PowerFC
- Bigger turbo (swedish, so name is irrelevant, 58mm), 21.7 psi @ full boost
- HKS wastegate actuator
- SARD 850cc injectors
- Z32 MAF, with Power intake
- Profec B spec II
- SSQV
- Removed EGR/AC
- Fuellab FPR 1:1
- Z32 fuel filter
- 3" TBE, decat
- Walbro 255 fuel pump
- HKS stage 1 cams

That's about what I can think thats relevant of this problem.. Dyno'd to 398 hp at the crank, untouched head.

Right now, I'm thinking it's either the O2 sensor (since the car runs better without it, but not perfect), coil pack (they do have about 80k miles on them..) or the MAF has gone faulty somehow. But then again, it's practically new.

Any help is greatly appreciated!

[0wn3r]

clean your MAF w/ MAF cleaner

[kcvpr]

Well, I would replace the O2 sensor anyways... They are relatively cheap (over here anyways), and since it runs better with it disconnected that makes me think its sending a bad signal. Also it probably isn't running perfect when its disconnected because its disconnected and obviously not getting the O2 level signal...

Anyway, that's just my idea of whats going wrong... I would wait till someone who knows more to speak up...

[sqd]

clean your MAF w/ MAF cleaner

That might be a good idea, you really think it would run better without the O2 sensor if the MAF was dirty? I personally don't have that much experience with MAFs and their correlation to other parts, for example the O2 sensor.

Well, I would replace the O2 sensor anyways... They are relatively cheap (over here anyways), and since it runs better with it disconnected that makes me think its sending a bad signal. Also it probably isn't running perfect when its disconnected because its disconnected and obviously not getting the O2 level signal...

Anyway, that's just my idea of whats going wrong... I would wait till someone who knows more to speak up...

Yeah, you're right, but they aren't that cheap around here, not "buy one for the heck of it"-cheap, for me anyway. But i could always order one from the states, only problem is it would take a week or two.

[kcvpr]

That might be a good idea, you really think it would run better without the O2 sensor if the MAF was dirty? I personally don't have that much experience with MAFs and their correlation to other parts, for example the O2 sensor.



Yeah, you're right, but they aren't that cheap around here, not "buy one for the heck of it"-cheap, for me anyway. But i could always order one from the states, only problem is it would take a week or two.The only way I could think a dirt MAF would have an affect on a o2 sensor would be if it was making the engine run rich and fouling the o2 sensor.

Also, I think the reason why your car would run better after you reset the ECU is because it has to find a new tune for the engine every time it is reset.

[0wn3r]

That might be a good idea, you really think it would run better without the O2 sensor if the MAF was dirty? I personally don't have that much experience with MAFs and their correlation to other parts, for example the O2 sensor.

I read your backfiring at higher RPM's and had a similar issue w/ my SR: slow accelerating to 4-5K rpms and backfired like crazy. It would also be hunting for an idle to, to the point where it would stall out

I can't view your video while at work, but it's like a $7 bottle of cleaner and one of the cheaper possible solutions.

[sqd]

I'll definately try it, though mine doesn't seem to have any problem with idling.

If you haven't viewed the video yet, please let me know what you think after you have :)

[s15specR]

Same problem minutes after changing to new plugs, rich as hell back fires around 6-7k rpms, just like you're experiencing.

[0wn3r]

who did the tuning? were you trying to reset the power FC?

[sqd]

The tuning was done by a pretty well known company here in sweden called Maxtuning. I emailed them, and they told me to be sure i was using the same plugs as they used when they did the tune (and I am, just not gapped exactly the same), and also pointed out that the MAF might be giving me troubles..

s15specR: Were they the same plugs as before? Same gapping?

[sqd]

Well, it's somewhat weird, but the problems SEEMS to be gone now.

I gapped my plugs to 0.028, fixed a tiny, tiny vacuum-leak, cleaned the MAF (even though it appeared to be squeaky clean), tightened all the hose clamps for the IC piping, reconnected the O2 sensor.

It started out running pretty badly, stuttering and so on, AFR was down on 10 during accel. But after about 5 minutes of driving around, it slowly disappeared. AFR is now between 11 and 12, wich it's tuned to, and no stuttering or problems so far!

It's weird, but seems to have been fixed. Let's just hope it stays that way :)

Thanks for all the tips and help!

[sqd]

I'd just like to bump my thread a little 'cause I figured out what the problem was. It came back the day after the above post.

The coolant temp sensor plug was halfway out of it's connector, making the PowerFC unable to read the temp correctly. It was flying all over the place, running up and down between 20 and 80c. Plugged it in correctly, and the car runs without any problems :)

Thanks for all the help and tips though!