I picked up a 94 jimmy with 4.3 vortex from an older gentleman on sunday. Only problem so I was told was the positive battery cable. Replaced with a new cable and everything was right with the world. Truck fired up and ran and drove absolutely great. It idled for about 5 minutes and I drive it approximately 5 miles. I pulled it up in front of the house so the kids could clean it out and wash it and that's where it all went wrong. The girls wanted to drive it down the lane so they hopped in and nothing. Battery was dead when I got it and it didn't take a charge. Threw another battery in and it just cranked and cranked but would not start. I checked fuel pressure and it was good to go. I pulled the coil wire off and I had absolutely nothing. I have a parts truck so after I checked to see that I had power going onto the coil with key on I proceeded to swap the coil with a known good one. Still nothing! So at the point i figured it had to be the ignition module so i robbed the parts truck and still nothing with another icm. So fast forward to today, i get home and hit the key and low and behold it instantly fires off. I bought a brand new ICM today so i naturally assumed that was the problem now that it runs with the engine completely cold. After installing it i hoped in and drove it about 10 miles and before I could make it back home it stalled out. It forced right back up but stalled speraticaly and then started surging while idlingin park and would stall completely when put in gear. Then once again it will not start and no spark from coil. I swapped out both coolant temp sensors because I've had that happen on my 5.7 vortec but no such luck. I still have power to coil but zero spark after it was good and hot. I have had it running with 3 different ignition control modules so I'm pretty certain that is not the issue. It has ran with 2 different coils with the same problem. I am lost as to where to go from here. I picked this up so the kids wouldn't have to walk almost 2 miles to the bus and now I've got a new lawn ornament instead.

 

Have you checked the ignition harness? They are a know problem area that fails right in the steering column, and they can cause all sorts of weird issues when they start to fail. The DIY section has a write-up on diagnosing and fixing this issue as well as a ton of other write-ups.