Maybe I can get some Ideas of what to look at.

I just got my trans swapped out, took a test drive and everything was great.

I took it to the store later and when I went to leave the store, the car wouldn't start. It acted like it wasn't getting gas, or maybe it was flooding. IDK Found the little rubber elbow to the fpr had a hole in it. Replaced with a spare I had in the car. No difference.

Went back to the car to try and pull codes and it fired right up.

It didn't throw any codes, I checked the fpr and the injectors for any leaking. It all looked good.

Took it for a test drive and it drove good.

Took it for another drive to datalog it and while cruising down the road the car just died. I tried to crank it but it wouldn't start. I coasted into a service road. Checked the datalog for anything unusual and didn't see anything.

Try to crank it again and it fires right up.

At least it happened when i was datalogging the car.

any ideas where to look first?

Here's the datamaster file if anyone want's to take a look for me:

 

Check it for fuel and spark. I've been having an identical issue and mine isn't getting any spark. I've had to replace my ICM 4-5 times because of this. If your car is getting fuel but isn't getting spark, get your ICM tested right after it refuses to start. Take it to multiple stores. If it tests bad, replace it. If it tests good, do a thorough check at your wiring system. Mine does the exact same thing and I think it's in the wiring. Please keep us posted.

 

Reads like the opti is dying a slow death. I had one like that and it didnt like heat. Then ive had optis that just flat die. Ive also had a ign control module fail too and that one just flat died at a stop sign.

My guess is the opti,
cardo

 

If I read Correctly you said they dropped the transmission and the problem started from there. Correcct? If so, I believe it might be associated with the NSS(Neutral Safety Switch). next time the car dies move the gears around and put it at neutral and see if it starts. If it does that might be your problem

 

But shouldn't the NSS prevent it from even turning over?

 

yea, thats true. Forgot about that one. Had to replace mine a few weeks ago for the same reason. Well hope you find your problem bud

 

Some more info on the issue.

When the car warms up it idles kind of rough. Been trying to track it down.

Replaced plug wires, and found a spark plug not tightened down all the way. Didn't really help.

I thought maybe it's the opti, changed the cap and rotor. Old one had a lot of carbon on the posts. Didn't really help much. The wheel and sensor area looked good, but that isn't an indication that it's not bad.

I replaced the ICM about a month ago, as the old one was literally falling apart. You could see the circuit inside of it! When I did this I also used a couple of small washers to space the ICM away from the head.

Last night I was looking over everything and noticed that the bolts holding the ICM were a little loose. I tightened them up. Maybe that was the issue?

I just don't know. I just want it to run right without just throwing parts at it. Guess this weekend I'll be under the hood with a multimeter, the manual, and probably some printouts from shoebox site.

:/

 

Having a newly replaced ICM does NOT mean it is good. I've had to replace mine several times because it continuously failed. Wait until it dies and take it off and to a local parts store as quickly as possible. It could be overheating like 4-5 of mine were, even with the cooling mod.

The spark plug could be the reason why it was idling rough. If it's still idling the same way, you might consider the ignition coil. Rough idling is a common symptom with those, along with a bad opti. But the coil is much cheaper. For a '94, you can pick one up for about $27 at AutoZone. If that doesn't work, I'd, unfortunately, consider the opti.

 

Yeah, I replaced the coil at the same time as the ICM, since it was cheap.

I'm really starting to think it's either the ICM or the opti.

Just wish it would throw a code. lol

 

Mine doesn't throw codes either. My CEL isn't even on. Did you ever check all the wiring?

 

Not yet, will try to do it this weekend.

I've got to figure it out. If I do happen to find anything I'll be sure to post the resolution.

 

Brian,
I have been through this twice in the last year. I quickly attacked the opti, but neither times was it the culprit. I know this through testing...shbox's website is a big help in testing the optical sensors signal being sent from the unit to the pcm, then fromt the pcm to the icm...You can check this by hooking up a voltmeter and seeing if the current is switching. It is supposed to switch between 1-4 volts I believe as it senses the disk. Granted it is an electronic piece and they can go in and out as they die slowly but it is an easy diagnostic test. The GM manual is a great detailed tool as well. I believe a corvette forum has a thread with some pages copied online about how to test the icm circuitry. Due to the opti being directly linked it backwardsly tests it as well.

In the midst of my testing the opti, I found that my 2 day old coil actually failed as I was unable to get the wire connecting from the coil to arc to a ground. (Had someone turn motor over while wire was disconnected from distributor and held insulated/plastic handled screwdriver in front of it=NO SPARK) Hence new coil. Installed and fired right up. May not be your issue but do that test next time it won't start and you can rule out the coil.

My ICM went out before that with similar symptoms to yours. My trick was pop the hood. Let her cool for 15min. and she would start back up til she was overheated again. Eventually she continually failed. All parts stores tested the failed unit to be functional. I replaced it eventually anyway, and have had no issues since. Lifetime warranty on the parts, although AC Delco would make me feel better even though it could be bad out of the box with them too.

Another cool test, if you conclude its your opti. Get a new one and before you install it, unplug the old one and plug the new one in. With the key on, spin the new distributor. The will at least let you know that the sensor is good on the unit and save you the hassle of installing a failed unit from the get go.

Hope this helps!!

 

It happened again today, car had been sitting for a couple hours, so it's not a heat issue. The car wouldn't fire. No spark. I changed the ICM to a spare I had in the car. Still nothing. I checked several connectors and after moving some wires around it cranked up.

On my way home it died, then I moved the wiring to the coil and the wiring to the opti, tps, and iac. The car then fired up and drove fine.

Think I have a short somewhere, and am probably going to start replacing connectors. They all look pretty ragged.

 

Search the two wires that go to the coil and search them good. There might be a break in one that you don't recognize as a break. I just found out mine has two of them. Feel around the wires and see if you notice an immediate sharp turn in it. If you find one, replace it and search the other wire. They seem to be a common problem considering the curve they have to make to go into the coil. Certainly hope this helps.

 

have you checked the ground on the fuel pump?? my car behaved the same way yours did and it ended up being a $5 fix lol

 

no, but I hear the pump priming when I try to restart it after it dies.

It died yesterday coming home on the interstate. I tried for quite a while messing with the coil wires, and the ICM wires, couldn't get it to start for anything. I moved the opti harness and it fired right up. I started home and about 5 minutes down the road it died again. I pulled over and was tugging on the opti harness and it pulled right off of the opti. The clip is broken. I plugged it back in and it started no problem. I ordered a new one and hopefully it resolves this issue.

 

PLEASE keep us posted. If it fixes yours, then I'll try replacing mine since my car is doing the EXACT same thing. Mine also looks a little beat up at the opti end.

 

Yeah I hate these kind of problems. Keep us posted!

 

I thought it was fixed, but guess it's not.
It died last night while I was driving. I was going about 30-40mph and rolled onto the throttle about 50%. It just cut off.
Same thing as before. It would just turn over and not start.

I tried messing with all the same wires as before and nothing. I then disconnected the opti harness connector near the intake manifold with the key in the run position and i heard what sounded like the fuel pump cut on.
Plugged it back in and tried to start it. It fired for a split second then died again.
I repeated this same thing again and it fired up like there was nothing wrong.
Just strange.

Unfortunately, every time this happens I'm by myself and trying to get somewhere and have no way to properly troubleshoot it. I always get it started and then when I have the ability to troubleshoot it won't die.

 

I just said **** it. I'm selling both the z28 and the Firebird.