Ignition problem with '92 GMC C1500

ignition
electrical-wiring
gmc

#1

I’ll start by saying I’m very much a shadetree mechanic. My knowledge is more than the average joe, but not by much. Brake jobs are no problem but I couldn’t rebuild a motor to save my life.
I’ve got a 1992 GMC C1500 with 158K on the odometer. Truck sat for about a year after I let the reg lapse. Started it up once or twice a month during this year with no issues. Got new reg on it and began driving it again. Within a week, the truck began cutting out while running. I could cut it off and then it would start right back up. Problem became worse over the next week or so until I got stranded. While trying to start it the last time, the ignition coil caught fire. Got it towed back to the house and threw in a spare ignition coil which doesn’t resolve the issue. A co-worker suggested the issue lie in the ignition module that sits under the distributor cap. I replace the coil and the module, truck starts up and runs just fine. I unplug the battery to wire a new temp sensor in and throw the top back together when I’m done. Go to pull it out of the garage and the truck won’t start up. I double check all my connections, they’re all good. Truck still won’t start.
I’m not quite sure where to go with it now. Could there be something that’s shorting out the module?


#2

Did you use the little tube of silicon grease when you installed the new ignition control module? The grease acts as a “heat sink” to keep from frying the module. Actually…a better idea is to use a silicone sealer instead of the silicone grease. It’s a tip I discovered back when the HEI distributors were first installed in GM vehicles.


#3

I made sure all my connections are lubricated, used the whole little tube of grease that came with the module.


#4

I think @missileman was refering to applying a thin layer of grease on the bottom of the module surface so it can transfer heat better to the surface the module rests on. That is what it is for, not for connections.

Another thing to check may be the voltage of the alternator while the engine is running around 1,500 RPM. Perhaps the voltage is going beyond the 15 volt DC limit. Checking the AC voltage also would be good to do. It should not go beyond .1 volt AC. If you do that make sure your meter blocks DC in the AC volt mode. Measure the battery while the engine is off. If the meter shows voltage present you will need to add a .2 ufd capacitor in series with one of the leads to block the DC component. I think you possibly may have some bad diodes in the alternator which caused the coil to burn up.


#5

Confirm that the coil is correctly mounted and well grounded and the plug wires, cap and rotor are in good condition. Spiking secodary voltage and/or poor grounding at the coil can cause damage throughout the ignition system and even the ECM.


#6

@cougar Yeah, the metal plate on the bottom of the module? That’s what I meant.
And I can’t believe I didn’t think about the alternator possibly causing the issue. I’ll throw a voltometer on it later today and see what that shows.

@Rod I’ll go back and make sure the mounts and all are tight. I didn’t see any wear on the cap or rotor when I had it off. Shouldn’t have been since I replaced both last year.