Now, is it that the tester is on the coil and your grounding it somewhere? Or is it that you're not getting spark out of your distributor cap? How are you testing for spark?

 

Fair question. Here's what I'm doing. First, I have it all put back together and crank it and it never fires. So I pull the wire off the distributor that's coming from the coil and plug a spark plug into it. I then hold the plug up to the block/ground and have someone else crank it over. I did this at night with my light off and didn't see any spark.

I check the four wires going into the coil with a light tester. One end clipped to ground and I just poke through the wires as they go into the wiring harness at the top of the coil. All four of them pulse rapidly when it's turning over.

I also pulled the wire going from the ICM to the coil and did a did an ohm test on both of it's wires and they tested just fine.

 

I stole this from a reputable website that specializes in mid engine GM cars.

This particular car shares the same ignition components as your truck, so what's in that post should apply. So in the end, you no have a new ignition module, clean terminals on the inside of your distributor cap and rotor, known good spark plug wires. You have a good ground (less than 5Ω) on the black-red wire and your negative battery post, the coil receives a 12V pulse from the pink (or maybe white) that goes into the primary side of the coil, the white wire (should be a pulsing signal with the spark timing) gets the same pulsing 12V. If all components are there, I would suspect a coil, or your plug wire. If all the components are there, then it only leaves a couple of things.

So, you tested and replaced your ICM, you replaced your coil and you still aren't getting spark? Make sure your spark plug wires are good. You should get spark right off of the end of the coil's wire that would otherwise go right into the center of the distributor.

 

Here's the latest. I don't have a spark tester handy, but I've been testing it just like you said except I'm grounding a spark plug to the engine block. No spark coming directly from the coil. I also tested the 1 foot wire going from the coil to the distributor and I get about 4.3k ohms. The cable is fairly new and looks good overall on the outside.

I tested all 3 of the coils I've got and each one of them are within the primary and secondary resistance ranges that you have in your diagram.

I checked the pickup coil in the distributor and got about 800 ohms between the 2 wires. Testing between each terminal and ground showed no continuity.

I talked with someone else and they told me to check the service engine light. When I turn the key on, the service engine light does stay on, so I checked it using the paper clip method and it just keeps giving the 12 code over and over which, as I understand, means everything is ok. He also said to check inside the distributor and make sure things are spinning correctly when it's turning over. That looks good too. Finally, he said there was an inline fuse on one of the wires that comes through the firewall and goes to the one port of the ICM. I couldn't find a fuse. In fact, the only in-line fuse I could find was one for the fuel pump. I'm assuming that's what he was referring to.

He offered to drop off a manual for the engine, so I think I'm going to check that out and see if there's anything else in there that I haven't tested yet.

 

How much resistance is there between the block and the negative battery post? I'm wondering if you are having ground issues, especially after reading your first post. Maybe double up your ground to the coil and run a jumper wire from that ground straight to the battery post temporarily for testing sake. The ground you mentioned in the first post.

Because it looks like we covered all of the spark components and all seems to be okay. Well, spark has to get back to ground, and your plugs ground through the cylinder head. Electricity always wants to return to ground, so if your engine ground is poor ... Just throwing some ideas out there.

 

The truck is running now. I brought it to a local shop. The guy said he ended up replacing the distributor and cap as well as the wires going from the ICM to the coil. He said that the distributor was "floating". Not sure exactly what that means, but he showed me the distributor and shook it and it made a little bit of a clinking noise. He claimed that he wasn't getting anything out of the pick-up coil wires and he showed me the contacts inside the cap and they had a tiny bit of white on them.

My hunch tells me that he decided to replace distributor first and it still didn't start, and then he ended up finding the bad wire between the ICM and coil. Maybe not, and I guess it doesn't really matter. Worst case here is that I have a new distributor and a running truck. Thanks everybody for all your tips and help with this one.

 

So here's my saga, 96 k1500 w 400,000 miles, would stall after driving about 15-20 minutes, no spark until it cooled off. I replaced the ignition coil, ignition module, distributor, cam sensor, vacuum sensor, crank sensor, eco, disabled air bags, re wired many grounds, but now I suspect it's the timing chain. Taking the cover off, it's so slack it's almost slapping against the engine block. About to replace it now. I would suggest maybe replacing yours, too, especially a 91.