86 K5 Blazer Intermittent Ignition Problem
 

I have an 86 Blazer using it as a off road plow rig so ther are a lot of things missing on this beast. Just recently started it up getting ready for winter and started fine drove it to my garage and parked it. Next time I tried to start it it just turns over like no spark or gas. There is plent of gas but no spark. I worked on it all last week and finally replaced the ignition switch down on the steering column. Put it back together and bingo:icon_hyper: started in like a charm. Started it a couple more times drove a bit then parked it about 5 days ago. Just went out to start it today and nothing.:icon_doh: Just like before. Gas but no juice (spark). One interesting thing happens when I turn the ignition off at a certain point in the ignition switch travel the engine will fire on one cylinder. You and see the fan spin about 60 degrees of rotation like the plug just fired in one cylinder that somehow got the spark.:icon_screwy: Anyone got any ideas? :icon_deadhorse:

Firing on one cylinder doesn't really sound much like an ignition switch problem. The coil either would be getting juice or it wouldn't be. Being an 86, you likely have the HEI distributor. This distributor should have +12V to it when the ignition is on. If you back probe the ignition +12V wire with a test light, does it stay lit up while cranking? If it does, the next thing would be to monitor the voltage on this wire with a multimeter (or just start out with one instead of the test light). If it stays close to battery voltage then the problem is most likely in the coil or possibly the ignition control module in the base of the distributor.

I checked that once and it was ~ 7-8 volts and it stayed that way during cranking.

Track the wire back to the ignition switch. You may have a wiring problem. 7-8 volts is not enough to properly power an HEI distributor.

Well the saga goes on. Plenty of juice going to the distributor but nothing coming out. I have replaced the ignition control module and the whole distributor, Still no spark. The only thing left in the ignition circuit is the computer located behind the glovebox in the cab. Anyone think that it could be the problem.