Intermittent Misfire. Low Rpm + Boost.

[DanShirts]

It is a mostly stock 89 R32 GTR. Basic bolt on mods; intake, zorst, gutted cat, boost is at 1 bar.

Here we go.. I've been having this problem off and on since I bought the car 8 months ago. It misfires below 4k rpm AND there is boost. No boost, no miss. It might be missing above 4k, I just stop feeling and hearing it around that point. It is also running slightly rich. I don't have a wide band so I can't exactly how rich. Idle bounces a little from 850-950.

Since I bought the car I have changed: plugs (twice), fuel filter, ignitor, air filters, turbos (stock R33), all exhaust gaskets, Lambda (O2) sensors, PCV, ECU, some broken vacuum hoses, and all fluids.

The first set of plugs I used were NGK BKR7E. They looked a little sooty after 6 months. I replaced them with NGK BCPR7ES. Tried gapping at 1.0, 0.8, and 0.6. It runs best at 0.8.

No boost leaks. I have cleaned & resoldered the MAFs. TPS measures 0.47v at 0% throttle and 3.96v at 100%. Coils ohm out between 0.8 and 0.9 and I didn't see any cracks them. I swapped coils around and pulled coils one at a time. It doesn't seem to be any one cylinder. I have done a motorvac on it (kind of like running straight injector cleaner).

Every time I cleaned or replaced a part, it helped. But it didn't clear up. I'm at the end of my mechanical ability. What can I do next?

Sorry if this has been covered before. I searched, but everyone else fixed misfires by cleaning the MAFs or closing boost leaks.

[blur]

Its a long shot but have you checked the earths, battery terminals and alternator output? Have a look at the ecu plug too, try disconnecting and reconnect making sure the plug goes on nice and square as your tightening it.

[DanShirts]

Its a long shot but have you checked the earths, battery terminals and alternator output? Have a look at the ecu plug too, try disconnecting and reconnect making sure the plug goes on nice and square as your tightening it.

There is a back wire coming from the main engine loom that earths to the ignitor housing. It ohms out to 0.5. Everything else is good.

I don't see it on the wiring diagrams. Any idea where it goes?

[DanShirts]

There is a back wire coming from the main engine loom that earths to the ignitor housing. It ohms out to 0.5. Everything else is good.

I don't see it on the wiring diagrams. Any idea where it goes?

Just talking to myself again...

Spoke to an auto-elec. He says that the wire is OK to measure 0.5 because it looks like it provides ground to another device. I'm just reading the resistance of whatever that device is (probably a circuit in the ECU).

Also, he said to replace the batter cables (because it's cheap) and to test the coils and coil loom after the car is warmed up. What an eye opener to talk to someone who really understands electronics.

Any other thoughts?

[blur]

The main ecu earths are on the the top of the engine, bolts to the top water outlet near injector 1, 2 x 10mm headed bolts. Run another earth cable from there, to the ignitor and back to the battery terminal, keep them all on the same ground.

[DanShirts]

Pulled another earth wire from battery to ignitor and also jump it down to the aluminum rail that the coils bolt to. Remade some joints that looked questionable. That one wire measured 0. Went for a drive, no improvement.

I borrowed a set of split fire coils. Still no improvement.

I'm still going to get new battery leads, but I don't think my problem is with earths at this point.

So I've been thinking.. Fuel pressure regulator? Leaky injector? Ignition signal from the ECU? CAS?

I'll check all those out next weekend. Anything else I can try?

[r34vspec]

i got the same problem with my r34 gtr ive checked what you have checked aswell have you found the problem? i was told that the coils are very common aswell that my next step?

[DanShirts]

Update!

Took the car to the parts store to pick up a new fuel pump. Only about 2k away. On the way back she back fired out the exhaust worse than I have ever seen before. Then stalled. I'm only 1/2k away from my house so I start it up and try to limp back. It only gets about 30m and stalls again. This time it won't start again.

Did the obvious: checked connections, battery, fuel, etc. This car is really starting to frustrate me.

Any advice?

[blur]

Boost leak?? Afm??

[DanShirts]

Boost leak?? Afm??

No boost leaks, I used one of those pressurized boost leak testers. I will read the FSM an do some diagnostic on the AFMs. Although I have cleaned and resoldered them already.

Got it started and limped back home. I swapped in the new fuel pump. It runs way better. Probably another 5-10kw, but it still misses.

[R.3.2.G.T.R]

u running stock ecu?? try resetting it.. have a look at your injectors, if there is a leaky one, it will be the cleanest looking one

[DanShirts]

The service manual says the MAF signal wire should be 1.1v at idle. Mine jumps around from 0.92-0.98v. Loom wiring looks good. Are they stuffed?

Stock ECU. I have reset it. No codes either. How do I check my injectors? Just pull them out and look? (Is that a stupid question?

[R.3.2.G.T.R]

no need to pull it out, just visual inspection, tried swapping maf with known working one?

[DanShirts]

All the injectors look equally dusty. I never noticed before, but one looks like the wires have been repaired.

I don't know anyone that can swap mafs with me.

[DanShirts]

Bumping.

Am I looking in the right direction? MAFs bad or is there another reason why they measure low?

I just want a thumbs up before I buy MAFs.