Stumble problems

Lostsoul71 · Dec 10th, 2012, 04:45 PM

Need Help any ideas welcome and Thanks ahead of time! Ok I have a 1987 300 zx non turbo, v-6, 5 speed. New oil pump, timing belt, plugs and wires cap button, new head gaskets worked heads intake upper and lower etc. Ok here is the problem it stumbles between 1400 and 2500 near to the point of shutting off. Acts like (A) lack of fuel or and (B) lack of air. Cleaned mass air flow sensor, Checked Belt timing, Checked distributor timing, set at 20 before top dead center, Checked idle set at 700 rpm, Replaced all Vacuum lines, Checked to make sure no vacuum leaks, has 35-45 p.s.i. fuel pressure. Has good exhaust pressure, will idle and rev without stumble but under load as driving stumbles.

BeyondBiscuits2 · Dec 10th, 2012, 07:24 PM

I'd recheck your timing just to make sure it isn't a tooth off. After that, I'd check all of the intake piping. I've had trouble with mine stumbling at idle when cold, but it usually corrects itself once it warms up. You might also try having a professional fuel system cleaning done to eliminate the carbon in the intake. The VG30E is a carbon monster, so that could also help.

Lostsoul71 · Dec 10th, 2012, 07:52 PM

Quote:

Originally Posted by BeyondBiscuits2

I'd recheck your timing just to make sure it isn't a tooth off. After that, I'd check all of the intake piping. I've had trouble with mine stumbling at idle when cold, but it usually corrects itself once it warms up. You might also try having a professional fuel system cleaning done to eliminate the carbon in the intake. The VG30E is a carbon monster, so that could also help.

Had the upper and lower Intake put in the Vat when had the heads reworked. The warmer the car gets the more it stumbles. Once above 30 mph all seems ok. Had the injectors cleaned also. I just rechecked the Belt timing all is good with it. Replaced the FPR also. Checked the compression all with in few psi of the same. Checked the TPS in specs. Now I have not checked the fuel pressure as driving but seems good as I rev the engine parked. But Thank you!

i r teh noobz · Dec 10th, 2012, 09:10 PM

Any codes?

The CHTS and subharness are known to cause all kinds of weird issues.

Lostsoul71 · Dec 10th, 2012, 10:24 PM

Quote:

Originally Posted by i r teh noobz

Any codes?

The CHTS and subharness are known to cause all kinds of weird issues.

Not yet checked for codes plan to check that tonight as I have been at work and will go home tonight after 5 days out. Thank you!

Lostsoul71 · Dec 11th, 2012, 01:55 PM

Quote:

Originally Posted by i r teh noobz

Any codes?

The CHTS and subharness are known to cause all kinds of weird issues.

Ok the codes I am getting are the idle switch and crank sensor and 0/2 sensor and detonation sensor Thank you!

i r teh noobz · Dec 11th, 2012, 06:34 PM

I'd check the idle switch and CAS codes first. The FSM should have step-by-step tests for those circuits.

xenonz31.com has FSMs available in PDF format.

Did you change your ECM at any point? My 88 manual shows the detonation sensor code as being turbo only.

Lostsoul71 · Dec 11th, 2012, 09:00 PM

Quote:

Originally Posted by i r teh noobz

I'd check the idle switch and CAS codes first. The FSM should have step-by-step tests for those circuits.

xenonz31.com has FSMs available in PDF format.

Did you change your ECM at any point? My 88 manual shows the detonation sensor code as being turbo only.

I have not but I am not the 1st owner of the car. I am the 3rd owner so no way to truly know the history of the car for what work might have been done over the years. I found it odd there was a detonation sensor code too. But unless I am counting wrong 4 times I got 3 red and 4 green. Thank you very much for your time and Info.

BeyondBiscuits2 · Dec 12th, 2012, 10:06 AM

Have you performed a compression test with the engine warm? Hesitation when warm sounds a bit like a compression leak, but I am just guessing. How many miles are on the engine? I know you said you had the heads off, so maybe the head gaskets didn't seat properly. I had the same problem on my Sentra... ran fine when cold, but once the engine warmed up and the metal expanded, started bogging and sputtering. Turned out to be No.1 cylinder hadn't sealed properly. Re-did the head gasket, problem fixed.