1994z28ss

I have a 1994 z28 camaro. The engine was replaced with an lt1 out of a WS6 trans am before i got the car. Recently it died and would not restart on my wife one day while I was at work. She left the car and when i got to the car 30-45 min later it started fine and rand 2 min and stalled. The next day I started the car and drove it home 10 min away and it stalled 2 min after getting home. The car will idle 5-15 min now then stall and will not restart. I did some basic diag and the fuel pressure tests fine when it stalls. After testing with some noid lights, i found that after it stalls and tryin to restart the comp is not firing the injectors. I am in the process of tryin to find a scan tool to borrow to check farther. I was just wondering if anyone had had/heard of this problem and knew a possible solution.

1994z28ss

I forgot to mention that i recently had to install a switch to manually operate the cooling fans because the computer was not operating them correctly. Is it possible/common that i may have a bad ECM.

Injuneer

Without scanning it, you're just guessing.

What were your exact fuel pressure results?

What was the PCM doing with the fans - not operating them at all? .... not operating both of them? ..... not turning on at the normal programmed temps (226*F low speed - or 1st fan, depending when in 94 model year your car was made; 235*F for high speed - or 2nd fan)?

1994z28ss

I do not remember the exact fuel pressure results as it has been a few weeks since the testing but I compared my readings with AllData and my readings were right in spec.

The problem with the fans was the guage would go all the way the into red and fans would never come on. You could unplug the coolant temp sensor(simulating a very overheated engine) and both fans would run, tellin me the wiring, relays, fuses, and pcm grounds were good, leaving only the temp sensor to be the fault. It was replaced and nothing changed. I talked to a friend who had the same problem and he said after changing the fan turn on speed with an aftermarket programmer they began working properly, leading me to believe it is an ECM software problem.

1994z28ss

*Fan turn on temp, not speed*

1994z28ss

I did some more testing today and i noticed that after the car stalls and you try the restart, the tach goes crazy with the switch on. Also it sounds as if the injectors are firing when the tach does this.

Is there any way to pull the codes out without using a code puller. I tried shorting a and b terminal and the fans kicked on but the light never flashed.

1994z28ss

I read several forums on the internet today where this was repaired by changing the ICM, so i decided to do my own testing on the ICM. I let the car run till the problems started, then i put the ICM in the freezer to cool it quicker than the other items. After putting the ICM back on the car would only run 2 seconds before dying. So i have a feeling its not the ICM. I think i may be looking towards th Opti. I may still replace the coil and ICM before installing the opti but im still open to suggestions on anything anyone can help with. I still havent ruled out the ECM.

Injuneer

You can't flash the codes on the SES light by shorting the ALDL pins on any year after 1993. You need an OBD-I scanner, or free OBD-I scanning software and a cable to connect to your laptop. TTS DataMaster and FreeScan will read your PCM. AKM Cables sells a cable.

Let's get back to the coolant temp sensor. Which one did you replace - the one in the head for the gauge, or the one in the water pump housing for the PCM?

1994z28ss

One in the water pump for the PCM

Guest47904

A code 16 which is the low res signal failure shuts off the injectors. But it shuts the fuel pump off also. So time to get the codes. You seem to think the fuel pump does not shut off.

You never mentioned whether the SES light is on or not. The DTC 16 will set a code, shut off the injectors and the fuel pump but will NOT light the SES.

You need to confirm they are firing or not after the problem occurs.

I have yet to see a defective OBDI PCM. It just doesn't occur very often. Drop that idea.

If you have a certain time that the enigine runs good like first thing in the morning. Then warm up one item at a time with a blow dryer and test the engine for a few seconds at a time to find the bad component. Don't just throw parts at the problem.

It also wouldn't hurt to pull the wiring from the opti and take a look at it even though I think you have heat soak problem.

1994z28ss

The SES light never comes on until a few seconds after the engine dies(which i believe is normal right?) The injectors are not firing at least not properly after the problem is there. I checked it with a noid light a few weeks ago and would only get one flash ever 5-10 sec or so. The fuel pump runs when you turn the switch on and the fp never drops while running or after it stalls. With Key On Engine Off after the car has stalled, the tach will jump around between 0 and 2000 and when this tach does this it sounds as if the injectors are clicking even though Im not tryin to start the car. Is the Opti the only sensor used to determine engine speed and timing.

Injuneer

Yes. It determines engine rotational speed, and cam position. The PCM uses that info to set the timing for the injectors and the ignition, and to drive the tachometer.

1994z28ss

So by the way my tach is jumping around with the key on. The only culprits could be the Opti of PCM, and from what i have been researching these PCMs just dont go bad, so the opti is my problem?

Injuneer

Rather than demand an "absolute" answer from someone who is trying to help you, why don't you scan it, as has been suggested?

1994z28ss

Im not tryin to insist an answer sorry if that es what it seems. Im just tryin to understand this system as it is new to me. I will scan the codes as soon as i get a way to do this. You mentioned a cable earlier to connect to a laptop. How would I get one of these cables. Do they have a website??