72 C20 Dies, Very Intermitent

[ajsfirehawk]

72 C20 350 automatic. HEI distributor. New bug just cropped up last weekend, driving along, purring like a kitten at about 50 mph. Instantly it dies, no spark, just like I turned the ignition key off. Rolls to a stop, I turn the key to try and start it, nothing. Starter relay doesn't even pick, nada. I snoop around under the hood, nothing seems out of order. 10 minutes later it fires up like nothing happened, drove it 70 miles home.
Same scenario happened again Saturday. I pull apart the distributor, noticed a small crack in the top of the cap. Pulled the ICM and the heat sink paste only covered about 1/3 of the control module. Bought new, swapped them both after carefully labeling plugs wires. Happened again this morning. I'm starting to think it may be in the ignition switch. I did shoot some lock lubricant into the door locks AND the ignition switch about a month ago. Is is possible the lock lube is causing issues with the contacts inside the ignition switch? Other thoughts.
Next step for me is to buzz out the entire ignition circuit point to point. NOT looking forward to that exercise.

[Lee H]

Assume you checked and are getting 12 volts to the distributor? Bad coil getting hot and breaking down?
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[Rufton]

Originally Posted by ajsfirehawk

Instantly it dies, no spark, just like I turned the ignition key off. Rolls to a stop, I turn the key to try and start it, nothing. Starter relay doesn't even pick, nada.

If the starter doesn't work in addition to spark loss I'd suspect wiring. I would start truck and do the ole wire wiggle test; under dash and under hood. I would unplug and inspect main wiring terminal on firewall. I would start cleaning terminals at batt and work toward switch (just because under dash is less fun for me). I'd check fuse terminals for corrosion. I'd measure some volts and resistances for clues.

[ajsfirehawk]

Rufton, thanks, I hate it but I agree with you. Lee, I was thinking the exact same thing until I arrived at the parts counter to buy a coil and the guy behind the counter reminded me "If the starter relay/ solenoid isn't even picking, the coil isn't part of the equation yet" I have buzzed the coil out and it is .003 ohms. Nothing says it can't change when hot, but I tend to agree since there isn't any reaction at all to keying it over.

[Rufton]

I've cleaned most of the important terminals once on my old rides. Since they don't see much salt they stay clean for years. I use axle grease on electrical terminals now days. Used the fancy dielectric stuff in the past but doesn't seam any better.

[ajsfirehawk]

I've got a 350 auto in the truck. It should start in Neutral and in Park shouldn't it?

[ajsfirehawk]

Replaced the starter, fabbed a heat shield to protect it from the heat generated by the headers. Cleaned the oxidation of the fuse and the contacts in the fuseable link. Removed the Neutral switch, disassembled it, the neutral contacts in particular were really corroded. Buffed them all out with scotchbrite and the spring loaded contact. Everything seems to be AOK. Thanks to those who gave me high probability places to check the wiring.

[ChevLoRay]

This happened to me, so I'm gonna share in case someone else is having a problem.

Mine was simply that it would shut off like I'd turned off the ignition. As I reviewed everything that had occurred, it was after I'd let off of the gas as I approached a corner that I didn't have to actually stop at. As soon as it died, I'd throw it into neutral, while still moving, and it would restart. Drop it back into gear and go. I took it to a guy I knew and they replaced the module in the HEI. I had done it, too. Nothing seemed out of place. They couldn't duplicate the problem.

So, one day I was headed to WallyWorld. I had to stop at a light. Of course, it died. I cranked it but no start.

A nice lady pulled up behind me and began blowing her horn, after the light turned green and I hadn't moved. I tried again, but no start. Light turned green, her horn began to blow again, so I offered to help her. I said I'd honk her horn while she tried starting my truck. She.Got.Huffy. Go figure.

I had it hauled home on a roll-back. I went and bought an Xcell HEI. It was installed. It started and ran without anymore issues.

Upon checking the HEI that was removed, it was found to have a break in the wire to the reluctor. When letting off of the gas, the breaker plate would move slightly due to the action of the vacuum advance, causing the wire to momentarily break the path of electricity and it would die. Now I just need to replace the reluctor ass'y and it's a good HEI.

I wonder what that ladys' husband said when she got home.....

[ajsfirehawk]

Nice, my symptom was different in that the starter would not even try and crank or even pick the starter soleniod. Just dead, butmine has been converted to HEI and I did replace the ICM. I'll keep an eye on the wiring inside. I have to pull it out to install the Edelbrock manifold and carb sitting on the workbench. So a great item to check before reinstalling. Thanks for sharing