Susie's Z

Recently i traded a 98 GMC Jimmy for a !994 Z28 Camaro Lt1. My Wife's project car. It ran rough at first. I started learning about the LT1. I replaced the Opti spark ( with the AC Delco OEM ) ,water pump,coil, icm, tps,plugs and plug wires, map sensor, both coolant sensors along with variuos other sensors.

The car ran like a scalded chicken ....... for about a month. It would run great until it got hot, then spit and sputter and sometimes die. Exhaust leak on drivers side , causing O2 sensor to read lean, dumping fuel to the injectors. repaired exhaust leak, new O2 sensor.... Problem solved.
The car ran great again...... until the other day on my way home. It just died in mid stride going down the high way. towed it home. The ignition fuse was blown.... replaced it, the car started right up.

Took it for a very short test drive , got 2 blocks, it acted like it blew the fuse again, had plenty of spares, popped a new one in....... Nothing !
I got it home ... No spark at the coil.

I have tested the Opti spark harness... All good
continuity checked the coil..... All good
Tested the ICM .... B and C checked out OK
But A and D are not getting ANY system voltage !

Does this mean I have a bad PCM or could it be the tranny solenoid, its my understanding that is all that is on the ignition circuit.
Any help would be greatly appreciated ! Thank You !

GaryDoug

I would inspect the transmission connector for damage or loose wires. Also try to narrow down the search by identifying exactly what happens just before the fuse opens. For example: Is it when the transmission shifts to a certain gear? Does it ever open when the car is not in motion?
I doubt the pcm is at fault.

Susie's Z

That's just it . Its not blowing the fuse now;but still has no spark. And no voltage to the ICM besides the Opti pulses that tell the Icm to fire the coil.

GaryDoug

If the fuse isn't blown and there is no 12v at the ICM, then a wire is open somewhere or the fuse holder or ignition switch is burnt. Did you replace the fuse with the standard 10 amp one?
Measure the voltage from ground to the fuse terminals with a good fuse installed. If you get 12v, the open is between there and the ICM. If no 12v there, the problem is with wiring or switch.

Susie's Z

Got it. I will test this in the next few minutes. And yes i would only use the proper amperage fuse.i did notice on my cold air intake ,the actual metal edge of the filter had slid up under the edge of the fuse box,so i think you may be onto something. I appreciate you sharing your knowledge with me . Thank You.

GaryDoug

I forgot to say that the measurement has to be made with the ignition switch ON.

Susie's Z

Meter read 12 volts.

GaryDoug

Next check the voltage at the solid pink wire on the coil. No voltage means an open wire or a bad connection at C100, 10-position connector near the pcm. 12v there means a bad coil or bad connection between the coil and the ICM.

Susie's Z

Ok . Did that. Got 12 on the pink wire. tested at the pink w/ black tracer at ICM . 12 volts there.

Susie's Z

now all the tests are checking out. Icm A 12 volts B 1to4 ac volts (when cranking ) C 50 ohms or less with key ON. D 12 volts. but still no spark/

GaryDoug

Now my guess is that the coil shorted and blew out the ICM. You can have the ICM tested at an auto parts store that tests parts. Do you still have the old parts?

Susie's Z

Yes I still have the old parts. coil checks out in a continuity test .I have swapped them both out ;but never at same time. Will get tested.

Susie's Z

Could not get them tested. So I warrantied the coil and ICM. Both brand new, still no spark out of coil. Still passes all tests at ICM, Coil and Opti harness !

GaryDoug

Test for spark directly from the coil wire. If it's there but not at the spark plugs, the distributor cap could be bad.

Susie's Z

Getting 12 to the coil; but No spark at coil. I pulled the tail of the harness up going to the trans, both solenoid connectors were heavily oiled and dirty. I cleaned and separated wires and followed all wire up to where harness meets just over back of engine... Nothing ! Still passing all tests for ICM, Coil and Opti !

I did notice when it opened the fuse the first time it was downshifting to second. When it died the second time ( not opening the fuse) it did it right when it was up shifting to second. Could a bad tranny solenoid cause this. And if so could I disconnect the harness to them to see if im getting fire. And would I have to reset the PCM before i do so.