Thread: Ignition Control Issues

After doing all of this to my 92 Grand Prix I am stumped and need help.

Symptoms:
After removing/replacing the negative battery terminal the car drives great till it reaches operating temp, then cuts out randomly during cruise, acceleration and deceleration (complete engine shut off, not just one cylinder) and will die as you begin to stop the car. The furthest it has ever gone is 60 miles or so before it just dies completely (crank – no start). At this point we checked it for spark and no spark at any of the coil packs. We tested the pink wire feeding the IC circuit and it has 12V (but oddly it has 0.14V less than the rest of the car at all times).

Already Replaced with NAPA Echlin brand:
ICM (3 different ones), Crank Position Sensor, O2 Sensor, Fuel Pump Relay. I also fixed all broken vacuum lines and several half-broken wires and cleaned up the grounds.

History:
1992 Pontiac Grand Prix SE 3.1 4T60 trans, at around 169k miles the car just started to cut out randomly during cruise, acceleration and deceleration (complete engine shut off, not just one cylinder) and die as you begin to stop the car (sometimes it will drive perfectly for miles in between these little fits). At this point I repaired a few vacuum lines and put in an O2 sensor. Ran better for a couple of days then cut-out and died completely (crank– no start) with code 42 (IC Circuit). At this point there is no spark. Replaced the ICM and the same thing happened: 2 days and dead with code 42. Replaced the Crank Position Sensor and same thing (this time no code 42). Put in my OLD ICM - fired right up, 2 days later dead again. Bought ANOTHER new ICM and it almost didn’t even make it home (8 miles), cutting out (AFTER it warmed up) almost the whole way like someone were just turning the engine off-and-on repeatedly.
The car has good exhaust flow so I don’t believe the CATS are plugged, it also runs very strong.
I use this car mostly to run to town (~20 miles) to take my son to school and pick him up. It has left me stranded twice now (luckily never with my son there) so I need to figure out where this ghost in my system lies.

Does anyone have any ideas why it loses spark after warm-up on all 3 coil packs at the same time?

engine runs good but turns on and off like a lightswitch, sounds like a rotten connector/short/bad contact

did you test ohms on the wire with less volts

also you said "several half-broken wires" , did you have to splice some wires and ended up using a crimper, if so check the crimps over again

ect sensor unplug it. iat unplug it done

you say it cuts out when the car warms up to operating temp? unplugging said sensors will rule out any issues with the ecm. your car is not liking closed loop for some reason. try the test and report results.

Thanks for the tip Erik. I will do that next. Right now I have the wiring harness under the hood taken apart, going through every wire individualy. After I have figured out the voltage drop issue going to the ICM I will post results and move on to your plan (if necessary).

It may be a while as my son's birthday is tomorrow.

I wouldn't be worried about the .14V less. Not a big deal as long as you are near 12V.

Almost sounds like something is heating up and messing up. Meaning the heat or expansion of something. Maybe a wire etc.

Try starting the car and wiggling the various wire harnesses to see if one has a break and maybe the only time it is making contact is when it's cold.

Read up on your ignition circuit. Primarily how it starts. In the 96-03's I have read it and know that the ICM controls nearly everything for the first 10 seconds, then it hands things off to the pcm. If that's the same in your case, you should see spark in the first 10 seconds automatically unless the icm/crank/cam sensors or wiring to them is having anissue.