Ok so my 94 z28 still isnt running. Ive thrown basically everything possible at it and still nothing. The car can only idle for about 25 mins before it starts losing either fuel or fire and starts cutting out and eventually die. Its consistent on the amount of time it takes to die and it wont start back for a couple of hours or so. Im stomped and it has stomped everybody who has looked at it. I have replaced the opti, module, coil, pcm, plugs, wires, O2 sensors, Idle control.

I really need some input!!!

And i was wondering if someone could give me a link to see what the original opti harness looks like so i can make sure i have it.

 

You didn't mention anything about checking your fuel system...Try putting a fuel pressure gauge on the system and watching fuel pressure when the car begins to act up, to verity that the problem is not fuel related.

 

yeah what boosted said,i had a holley pump that would overheat alot and i changed it.problem solved.

 

Yea i forgot to mention, we tried a fuel pump and it didnt change it a bit. It has a fuel pressure gauge on the right side of the intake and it reads 40 to 45 every time.

I am having a guy looking at it for the past month and he said it was loosing crank signal to the pcm when it starts cutting out. I put a new opti on it, could the opti possibly be bad?

 

I noticed that you haven't changed the icm, or did you? it could be the icm going bad, motor heating up, and icm cutting out. could be the problem. it bolts up on the same plate the coil does..

 

Check the wiring harness that plugs into the opti. Your fuel pressure of 40 - 45 with the FPR vacuum line on? If so, that pressure's too high unless it's been adjusted for some reason.

 

Yea i changed the ICM, i listed it as module! But im not sure on the fuel pressure, this at the intake manifold. I have been told that is good fuel pressure. I dont think it has been adjusted but im not for sure.

Any more ideas?

Oh and the guy that is looking at it now was gonna take a look at the harness, he said it looked like the plug-in coming from the pcm end looked a little loose in the back of it.

But can anybody give me a link to what the original harness for the opti looks like?

 

I'm assuming you have a 94 lt1 by your name, 94s dont have a crank signal, if thats what the guy whos looking at it said, might want to get a new guy only 96 and newer have a crank position sensor and they only use it for misfire detection

 

Don't quibble.... the cam position, and pseudo crank position are derived from the high and low resolution pulse patterns from the Opti. Lose the low res signal, and the PCM shuts down the fuel system, including pump and injectors. Wasn't really bad advice.

 

Injuneer I'm not quibbling... if hes got a mechanic pulling the codes and the mechanic is saying theres a code for bad cps then hes got a mechanic whos not reading the codes right.

 

He didn't say anything about "pulling codes" or a CKP sensor..... he said it lost the crank signal when it cut out. That would be a failry accurate description of the PCM losing the Opti signal. That is the way it is described in some "generic" writeups. That's why people are suggesting he check the Opti harness, to insure that isn't the source of the intermittent low res pulse pattern.

 

Thank you Injuneer! Im brought it to this guy because he has alot of experience and works at the local dealership. He said he was going to check the wiring harness from the opti to the PCM, but if he doesnt find anything then im going to swap the old opti back in and see what happens, can ANYBODY provide a link to see what the original opti harness looks like? I have a MSD on there now so im not sure what i did with my old harness.


What if it is not in the harness, could the Opti be bad?

 

could have a problem with the pcm itself, 3 things needed for a car to start fuel, compression and ignition, i assume u have compression due to the fact that it starts eventually and runs for 25 mins. When its running, in that time frame is it running like nothing is wrong or is it stumbling or missing?
When it dies find out what you dont have. check for spark

 

No ive replacesd the PCM already and no change. The problem of running and then eventually dieing after a time period started after i put the new opti on. Before it would miss above like 3k but it never died. I know i have fuel because the in line guage at the intake still reads the same it did before it died, unless it is the injectors then i wouldnt claim it to be fuel.

And during the time frame of running it runs a little choppy for a couple of mins then smooths out until it starts dieing then it just sputters and wont take any gas.

 

Nobody else?