Hi guys I have a question/problem that has me stumped and I can't seem to figure it out. Car is a 94 caprice/LT1 that will crank fine but will not start. It has no spark at the ignition coil. I have probed the wires at the ignition module and get the appropriate voltages at A & D, ground at C but I am not getting anything at B. I know that this pin (B) is connected to the black connector pin (5) at the pcm. I believe this is the signal from the pcm to the coil. I have checked this wire for continuity between the pcm and module and it is good. The pcm, coil, fuses in the underhood box and module are all fine as I have repeatedly swapped them between another vehicle and they all work fine in the donor car. My question is, short of removing the engine harness from the car, are there any wires specifically that I could check on the harness that would result in this situation.

Thanx in advance,
John

 

The wire on terminal B of the ICM is the trigger signal from the PCM. While cranking the engine over, it should have a signal from 1 to 4 volts AC. Not DC. It is a pulsing signal. If you looked at it with the meter set to DC you won't see it and if you just had the KOEO, there won't be anything there either.

You have to observe that signal WHILE it's being cranked. If it's not being provided by the PCM then the reason would be the PCM isn't getting the feedback signals from the opti. However, if the feedback signals are not received by the PCM it will set a DTC. BUT the low res will not set the SES light(at least in F bodies it doesn't). So you could have a code, but the SES light may be off.

Scan it for codes. Then start by looking at the signal on B while cranking and meter set to AC. If it's not there, look at the feedback signals from the opti. If they aren't there, it's usually due to connector corrosion or wiring issues.

Dave