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94 Z28 cuts off and won't crank back up? HELP!

3533 Views 16 Replies 5 Participants Last post by  fast94camaroz28
It's a 94 Camaro Z28 with the LT1-A4. All stock except for gutted cat and a K&N air filter in the stock air box. We have replaced the Both Head Gaskets, Whole Opti-Spark (AC Delco), both O2 Sensors, MAP Sensor, Coil, ICM, Wires, Plugs, Ignition Switch(on the column), Battery (Checked all grounds also) and now it will not stay running. You can burn the tires off of it and then try to crank it 30 mins later and it won't start for nothing! :craz28: :dontknow: No SES light or any light on the dash. They come on but don't stay on. I have tried a reprogrammed PCM and it still won't crank. IF it does crank, it will run lass than 10 seconds and shut off. It has been at Mayhem Motorsports for 6 months last year and they have been stumped by this!! ANY help is very much appreciated!!!

Thank You
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i don't see an ignition control module on your list (it lives on the coil) and that's a typical mode of failure for that part, especially if it was installed without thermal compound between it and the coil bracket.
Sorry that was replaced also. They did put the grease on it. Thank You for pointing that out.
If icm, opti low resolution pulse was missing, it would not light the ses, but there would be a code present. These codes also shut down the fuel injectors when present.

And speaking of fuel, have you tested your fuel pressure, or tested to see if injectors are opening.

And that brings us to the security system. Is the security light coming on for a few seconds then going out when ignition turned on? Or is security light staying on, or even not working at all?
Yes they checked the fuel pressure and they checked the injectors with a noid lights. The security light comes on like it is supposed to.

I just went out and it fired up. But before it cut off, the rpms jumped from 1000 to 1300 3x then it shut off.

This car is driving us crazy!!!
When it won't start, determine what is missing-spark or fuel. At least that will narrow things down.
Will do. It's gonna be going back to the shop. When i push the valve by the fuel pressure regulator, fuel shoots out.

Is there anything else to check for spark on that car?

Also why are we getting 225 miles or so to a full tank of gas? Now that is not kickin it at all and it will not get more than 225 miles to a tank. What would that problem be? I have used Lucas Gas treatment and Sea Foam Green and it still doesn't get better gas mileage. Any Ideas why?

Thank You both for your help!!
Fuel pressure should be checked with a gauge and should be above 41 ps1 at key on prime. Pushing valve is not a reliable way of determining fuel pressure as it can squirt out at considerably lower pressures than engine needs to run.

Another thing to check would be your electrical part of the ignition switch. It's located under the dash, attached to steering column. Look for burnt connector pins, bad connections, etc. Also get wiring diagrams for your 94, and check for proper voltages on all outputs of ignition switch when problem occurs.

Don't have 94 wiring diagrams, you say. Then go to 4th gen section, look for thread titled "GM service manuals" open thread, click link and download factory 94 service manual. Volume 2 has wiring diagrams, component location diagrams, driveability, emissions sections. It even has a handy pcm connector symptoms chart that tells what happens with each pcm wire if it's not right.

Which brings us to checking pcm connections, power wires, grounds, engine grounds, etc, in your search for the offending object.

And don't forget to remember, just because you puta new part on the car, you can't eliminate the new part as a suspect. Test them all. Sticky threads of this section has diagnosing the opti video, with tests to run. also has opti tests and coil tests, as well as, factory manual you should download.

Note, the fuse that supplies the coil and icm, also supplies the automatic transmission with power. So a problem with the wiring, connector, pins, electrical components of the trans could draw down the power going to coil & icm and cause a no run situation.

Final note, arm yourself with knowledge, testing and troubleshooting techniques, and you will find your problem or problems using a systematic approach that leaves no stone unturned.
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Thank You Cocobolo. I have used and have it saved in my favorites. I have read tech articles until my eyes hurt. Ever since we got that car, I have researched all that I can. For 3 yrs now. This is the only problem that we have with that Camaro. Wish I had one of you guys closer to help find this problem.

But I do know a sure fire way to never have to worry about it again! With a BIG BOOM!!

Would the key chip cause this problem? Just tired of throwing parts on and it not fix it.
What is the best code reader to buy?
Actually, a scan program for your laptop or notebook would run circles around all but the most expensive scanners. And your in luck as we have a good obd1 scan program in the 4th gen section, and it's free. Look for the obd1 scan program thread. And it's specifically designed for 94 & 95 f-bodies.

But don't stop there, go to TunerCat and download the trial version of the scan program DataMaster. Good for 20 data logs and unlimited data play back. DataMaster kicks A because it logs sensor data runs into a file that can be played back. You can even upload the file to a sharing site and link it to the forum, where members can review the data and help you with diagnosis.

However, you will need a cable to hook car's dlc with usb port on laptop or notebook. Get at ALDL OBD1 OBD cable OBDI OBD2 engine codes $59 + shipping
Thank You Very Much!
OK It finally did it at the shop! It is the Opti-spark that is going out. BUT at least it's covered under warranty. :craz28::rolleyes:
Woohoo! now get that car on the streets and scare the sh$t out of everone! Ha!
Your discovery of the opti being bad reinforces what I've been saying for a long time. That is, "in troubleshooting, don't overlook any suspect, even new and nearly new parts".

Time and time again I see members dismiss the possibility of certain parts being bad, because they are new. And ending up discovering, the new part had failed.
Well it was like it would not mess up at the shop. But a day or 2 after we get it home, it would just shut off. We only put 5000 miles on it last year because I refuse to let my wife be stuck on the side of the road. She leaves for works at 4:30 am. I wasn't going to leave the shop until it cut off and not crank back.

Before you check any part on the LT1's, Check the Opti-Spark!!! Love the car but hate the problems! lol
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