Okay. I have a 95 z28 m6 with full bolt ons and for the last few months it has seemed to be one problem after another. A lot of people have what they think are ideas to solve this problem but nothing ever seems to work so I hope one of you guys can help. I will start my car and everything works fine, I can drive it and everything is just fine. Once it has gotten to temp and i shut the car off it wont start back up until it is completely cooled down. Sometimes it just shuts off while driving as well about 15 min after starting it but lately its just been it not starting once warm. I have replaced the optispark and then realized that when the problem was occuring the coil had no power to it so i assumed it was the pcm. Needed to get the car tuned anyways so i ordered a new pcm from Madtuner already tuned for what i had in the car and problem still occured so once again i'm out of ideas. Please HELP!!!!!! thanks in advance.

 

I'd suspect the ignition control module (ICM) suffering from heat soak.

The coil doesn't get it's power from the PCM... power gets supplied at 12V from the battery. The PCM supplies a pulse signal to the ICM and the ICM fires the coil. It's also possible something is breaking down in the coil lwhen it heats up.

A heat soaked optical cam position sensor in the Opti would have set a code. Did you check for codes at all before replacing parts?

Have you checked the fuel pressure?

 

Unless there are some other unmentioned symptoms (are there?) and if the coil truly had no power, you need to be checking out the circuit that feeds it power (fusebox, fuse and wiring). Though, I admit that the 12v supply to the coil is usually not a common problem. I guess it cranks normally, but just won't start? Fuel pump primes? Give every detail you can think of.

 

When the issue occurs it will crank like normal all day. just wont start. The fuel pump does prime and i pulled a fuel line off to check fuel and there was definitly fuel when trying to start. The problem is definitly spark. i just cant figure out where the issue is. Sometimes like i said it will just shut off going down the road and then start 5 min later. other times i will turn the car off after a drive and it wont start back up afterwards and when i say it wont start i mean like till the next day or at least till it completely cools down. I assumed ICM as well and had one lying around so i put it on the car and it made no difference. Someone told me when it happens to check terminal B on the ICM for power and there was none. That is when i assumed it was the PCM. After i replaced that from madtuner and the problem was still there i was absolutely out of ideas. I mean the only thing else i can think of is a bad ground somewhere but i dont even know where to start on that. Thanks a lot for the help. You have no idea how much i appreciate it. This is my 7th 93-97 LT1 Z28 and i have had some issues in the past............obviously. lol, but never one like this. really stumps the crap out of me.

 

by the way, which color connector on the PCM is the one all these wires for the ignition and ICM go to? Just wondering.

 

Shoebox has complete PCM wiring info and pinouts on his site, under the Electrical section.

4th Gen LT1 F-Body Tech Aids

http://shbox.com/1/1995_pcm_conn.jpg

 

First you said the coil had no power, then you said the ICM had no power. Which was it or is it both? When you look at the schematic, the 12v power travels: fuse>coil>ICM. So, the coil has to be plugged in before you can measure voltage at the ICM. If your coil was going open when it got hot, you would also lose power at the ICM. Of course, you won't get any spark from the coil if it goes open, no matter if the ICM is getting power or not.

 

Terminal B on the ICM is where everything gets its power from the PCM to ignite the spark correct? That is where my father and i tested and there was nothing. From the looks of the diagram, i cant see anywhere else a wire is going to the coil to feed power. I am really ignorant about all this because i just dont seem to know anything about whats happening. What do you think the next step should be? What exactly should i check?

 

Also, we never actually unhooked the coil from power, the first thing we checked when we realized it was spark was unhooked the coil wire from the optispark and gapped on a ground to see if there was spark and nothing, then we checked terminal B to see if the ICM was getting signal from the PCM. And nothing there. I see now how the battery power runs to ignition and then from there runs to the coil and then the ICM. I just dont understand what needs to be the next thing to check. Could this be a problem with my ignition switch? Some problem with the Key or a loose connection inside the steering column? Or is the issue at some other point. This problem is the weirdest thing ive ever seen.

 

The problem is you are not doing any productive troubleshooting. Tapping a power wire to ground is no good way to test for anything. It's just a way to blow a fuse. You won't see power on the wire from the PCM like that. You have to test it a certain way with a meter on the ac scale.

How to test...

 

I guess I'm just asking what you think I should test??? Where do you think i should begin. I have no idea what could be causing this problem right now and all i've done so far is throw parts at it which i hate to keep doing? Just tell me what to test and help me narrow down the possibilities. Thanks

 

tested the ICM connector after i got the car to not start again. both A and D had good voltage, couldnt test B by myself but tested C for ohms of resistance and it read like 30 or so. could this be a problem and if so where does that ground connect to? Where do i look to next. thanks.

 

The ground may go there on the coil stud, but not sure. Maybe you could trace it out. Can't say if 30 ohms is your issue. A ground is a ground, though and should ideally be zero ohms.

 

i could see that it went in to the loom that runs down the side of the intake manifold but i will look at that later. I guess the first thing i should do is eliminate the optispark first. If assuming all the connector wires on the ICM tested good and all the connector wires on the Optispark harness test good then my optispark is out of the water correct? what would be your next idea?

 

Nothing is out of the suspect list until you positively eliminate it when the trouble is present. The first thing I use in troubleshooting is a scanner. Monitor live data or datalog. When the engine dies unexpectedly or will not start, check for spark and fuel pressure.