ZebraEJ8

I have an 86 K5 Blazer with the factory 305 small block and factory HEI distributor. Lately when I try to start it cold it doesnt get spark when cranking, but it will spark once when the key is turned back to OFF. A couple days ago I went through all of the flowcharts in the FSM and took everything apart and tested it. When I put it back together it started up and ran fine. Its been parked since then and today it had the same no spark issue when I tried to crank it. Im all out of ideas as to what could be wrong with it, and I would greatly appreciate any input as to something else to try other than throwing parts at it.

Fabrik8

Checked the ignition switch assembly?

ZebraEJ8

No the distributor has battery voltage with the key on and while cranking, and the engine is turning over.

Fabrik8

If it's not fuel injected, there isn't really anything other than the distributor that could be the problem. You give it voltage and a trigger input and it outputs spark at angular intervals. So the module, coil, and magnetic pickup are really the only three suspects, assuming the rotating mechanical components are functional. You've probably got a cracked component or something with a thermal-dependent electrical problem.

You can replace all of the electrical components inside for about $70 total Summit with a HEI tune up kit IIRC.

ZebraEJ8

Yeah I'm building a 350 to go in it and I'm planning on getting an MSD street fire distributor to go with that. I know that makes trouble shooting this one seem redundant, but I still want to pinpoint the problem if I can. I don't see how it could be a thermal dependent problem because everything was cold when I tested it. The resistances on both coils were almost dead in the middle of spec, and I checked the waveform of the pickup coil as well. I tested the module 3 times and it passed all three times. I let the module cool down for a few hours before re-installing everything so it was still all cold when I put it back together and it ran.

Dough_Boy.

Ignition coil?