My car starts fine in the morning and will go maybe 5-10 miles with no problems. I will shut car off and restart an hour later and it will run for about 2-3 miles and shut off and not start. I replaced my MSD coil with stock unit and it does the same thing. When it does not start the coil gets no spark? The car will sit for 10-15 minutes and start for a few minutes then just die again. What makes the coil spark? Is it the computer or maybe the crank sensor. Opti was replaced about 6 weeks ago, wires and plugs are fairly new. I am getting no codes. I have a msd 6A ignition and went back to stock ignition and still does the same thing.Any ideas?

 

There is no crank sensor on a '94 so that isn't the issue.

Places to look:

1) The wire that connects the OPTI to the wiring harness. THe pins sometimes corrode leading to intermittant issues...right up until it stops altogether. Unplug the wire and clean the terminals and make sure the pins are straight.

2) The ICM, ignition control module, is another place to look as they fail due to repeated heat soak. You can remove it..it's mounted near the coil on the same bracket and have it tested at Autozone. Test it cold and after heating it with a hair dryer or similar. That will simulate the cold start/hot running your seeing.

3) The OPTI itself can be failing. If the PCM doesn't get the right signals from it the signal to fire the coil doesn't get sent. A new opti isn't a guarentee that it's OK.

That's a start....

 

Fixed. It was the Ignition control module. I picked one up from Autozone and it works great! Thanks to all who replied.

 

At any point did you scan it for codes? The ICM will set a code.

 

I don't have a way to scan for codes and my problem is back. I suspect the new opti is my problem? Anyone?

 

The Opti will set codes if it's a problem with the optical cam postion sensor. The optical cam position sensor sends a signal to the PCM, telling it where each cylinder is relative to TDC. The PCM uses that info to determine when to fire the injectors and the spark plugs. To fire the spark plugs, it sends a signal to the IC module on the white wire. On receiving that signal from the PCM, the ICM fires the coil.

If the optical module is not sending the low res pulse pattern to the PCM, the PCM shuts down the fuel system.

You need to scan it.

 

OK, I think am getting some where. I just drove the car for 4 miles(car sat for 2 hours), got it home, shut it off. Started car, ran for about 30 seconds, then shut off. Car cranks fine, but does not start and I am getting no spark from coil. Let the car sit for about 5 minutes and fires right up, runs for a few minutes then shuts down again. The longer I let it sit, the longer it will run. Any suggestions and where to get a scan tool for a '94 Z-28?

 

I almost promise you it's the Opti. I have the same issue on my car right now. It starts, runs for a few minutes, and very abruptly shuts off. If I try to restart it, it will crank for almost 30 seconds and then fire and set the SES light. I believe it sets a code 36 for me, no High Resolution pulse. Once the SES is set, it will run as long as I want it to...just not all that great. I've found if you put the gas pedal to the floor after it dies while trying to restart, it will re-fire. Otherwise, it wont.

With the Low resolution pulse failure, code 16 will be set. the PCM will shut off the fuel pump if this code is present.

Some dealerships will do a scan for free, some wont.

Also, have you checked your fuel pressure? It could be a faulty fuel pump.

 

Not 100% sure, but appears 2 relays were very loose. Car runs normal now without shutting off?? Go figure.