Help!! Stumble/Cut at 5000 RPM

[Purplehazedog]

Well I found and temporarily fixed the problem. I put in a new crank sensor and the car ran/stumbled/cut different. So I tried to gap it and it would move to much. I put a washer inbetween the bracket and CPS and WALLA! It was fixed!! I raced this weekend and it stumbled again I added a second washer to pull it away from the Hamonic balancer and its fixed.

Turns out, my Harmonic balancer wobbles just a bit and causes the CPS to be to close or lose contact only at high RPM. I will be replacing the Harmonic Balancer and that way I have a good contact at .040. And I can lose the washers.

So after about 30 hours of work and about $400 of parts. It took a .10 washer to fix my prob!! Haha.

Thanks for all your help guys.

[Purplehazedog]

Fixed the temp sensor and swapped out the harness. Problem is still there. I have a appt with a shop in the morning.

[Purplehazedog]

@Jlevie.... Yes the Tach goes crazy during the stumble. I do have some old wires around the temp sensors, my temp gauge just resently started turning on and off.

I think I have bad wiring somewhere and I bought a used 105K harness. I plan on swapping it out as soon as if arrives, Unless I can find the bug before the weekend.

I'm trying to find someone with a Oscilloscope here locally.

[jlevie]

If the fuel pressure remained constant during a stumble, the likely candidate then becomes a loss of timing data, a loss of injector or coil power, or a loss of injector firing signals.

Does the tachometer react by dropping during a stumble? That would be indicative of a loss of timing data and/or an interruption in DME power.

FYI: I had the same sort of problem on my first two SpecE30's. After numerous swaps of everything in the engine management system the third used harness finally worked, for a while before a short developed in the wiring to the ECT & temp gauge sensors. The car now has a brand new harness.

Ultimately the way I diagnosed the cause was with a battery power oscilloscope connected to the CPS input to the DME monitored by a passenger.

[Purplehazedog]

I just put a fuel pressure gauge on the car and it is consistant during the stumble. The gauge didn't move when the car would cut out. I'm going to try a volt meter next

[Purplehazedog]

I'm calling a local shop in the morning to have them check the fuel pressure, Air, voltage etc..... I've been crazy busy at work.

[603Racing]

Do you have an air/fuel ratio gauge in that race car? Fuel pressure gauge? This data would be helpful.

Going to quote myself at the risk of being an ass.

Testing fuel pressure should be one of the first steps, can save time and money. It's doubtful that injectors are the cause since you're only seeing this problem at high RPM... unless you do not have the correct injectors. Even though you swapped TPS, I would test that as Jim recommended. You need to determine what is causing your symptoms before you try fixing it.

[Kozworth]

the c191 is a ninja issue, its hard to really even see if the issue is there.

My friend had a c191 that looked fine, but where the wires met the male/female pins there was no connection. I would highly recommend just cutting the connector togather, and souldering in a custom one. Its easier then trying to trace back to the dme to ohm test the circuit.

[Purplehazedog]

Can my timing be off? I have not touched it. But can it move?

[FLG]

Ignition is controlled by the dme.

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[Purplehazedog]

Is there an ignition module? On these cars? I'll check fuel pressure next.

[FLG]

No there is a cap and rotor. Which op has changed. Op have you confirmed fuel pressure?

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[saturnv7890]

The rotor bolts to the cam gear directly. There is no distributor. The DME takes care of the ignition timing.

But there is still a distributor for the sake of the spark getting to the right cylinder still? Unless this is a m42?


Anyways it might be worth it look for pitting on the distributor contacts if you haven't already.

[EatsHondas]

A buddy of mine says I should try to swap out the Distributor. What do you guys think?

The rotor bolts to the cam gear directly. There is no distributor. The DME takes care of the ignition timing.

[gath]

I had an issue with stumblling after 3000rpm for some time after warming up, changed a lot of stuff with no luck, until I put a new coolant temp sensor.