Keep Frying HEI Coils PLEASE HELP!

[TyTexan]

Ok. I am brand new here. I have never joined any of these groups because I usually search the web and find someone who has had a similar enough problem and there were enough answers to point me in the right direction. But I am at a loss I hope you guys can help me on this one.

I have a 1986 C20 with a 350. Everything is stock. A good classic old truck in pretty good shape. Was running well and suddenly died one day about 2 weeks ago. No spark. Opened up the coil cap (has the in cap coil) and the coil was physically melted. Had melted plastic coming from within the coil. Swapped the coil and it immediately fired up, ran well. Ran for about 3 days and suddenly died again. Opened up the cover and another melted coil. This time I changed all the plugs and wires, rotor cap, new distributor cap, checked the ground to engine on the ground strap. I tested my alternator, it tested fine, but was making a funny noise, so I replaced it anyway. I though I might be getting too much voltage to the coil. Put it all back together, fired right up ran well for about 5 minutes and fried another coil....ARRRRRRGGGGGG! Coils aren't terribly expensive, but at 40 bucks a whack on top of all the other stuff I've replaced, this is getting frustrating.

I don't suspect a bad ignition control module as every time I put in a new coil, it fires right up and runs just fine. Something is causing great heat to my coil, melting it and shorting it out. I know over voltage or bad ground will cause the coil to over work and over heat. But with good battery voltage, and a good ground with the ground strap in place, I am at a loss. New plugs and wires shouldn't be causing the problem. What's worse is that it seems like the failure time is getting shorter and shorter.

Any ideas, tips or pointers?

 

[78C10BigTen]

Just a dumb question how many ground straps does it have from the engine?

 

[TyTexan]

I haven't checked the ground straps between the engine to the frame. The ground strap I'm referring to is the ground strap that grounds the coil frame to the wiring harness. That ground prong has zero OHMS to both the engine block and firewall.

 

[mtnmankev]

I can't see how it could be getting too much voltage unless the alternator is kicking out way too much power or you have a bad or missing ground somewhere.
.. and those coils are designed to run on 12.6 volts plus or minus a bit, as compared to the old school points coils that start on 12 volts and run at 9.6
I agree the grounds all need to be verified, battery to engine, battery to frame, battery to body, engine to body, engine to frame and frame to body.
I assume you are coating the large rubber washer thingy at the base of the coil with dielectric compound ?
That shouldn't matter, but it might cause an issue in a rare instance.

Welcome to the forum, and keep us posted how it goes.

 

[Curt]

One thing that kills electronic components more than anything is low voltage.

I would change the control module out if your voltage is good

 

[TyTexan]

No I didn't ever put dielectric grease on the washer. I didn't even know it needed it until I was reading more. I agree that it shouldn't be a deal breaker. The module is probably the last thing. At this point though im seriously just considering putting an entirely new aftermarket distributor. Gonna do some shopping and evaluate my options. By the time I do a module and another coil, I'll be a long ways into a completely new aftermarket set up.

 

[Rusty Nail]

I'd be pretty quick to buy a new distributor , it's much more simple than actually replacing the pickup coil (if you could even find one for sale) and will include a new module.

Good luck.

 

[Dave M]

I'm following this thread hoping to learn something about HEI distributors. Beware there are some cheap and nasty replacement distributors out there, do your research, ask questions.

 

[jake wells]

The el cheapo distributors from ebay are garbage.

 

[jake wells]

I have seen when ignition control modules are about to **** the bed will usually take a coil with it.
It happened on my 75 last year.

 

[Vbb199]

I vote bad grounding, or super sloppy dizzy.

Maybe module, but kinda doubt it.

Truck wouldn't start if module was dying I'd think.

 

[1987 GMC Jimmy]

What brand of coil are you using? They should come with a ground strap and a ground wire. According to the Standard Motor Products literature that comes with their Blue Streak line of ignition coils, you can burn them out prematurely without both grounds in place. It’s also possible that the ground is somehow open on one or both so I’d see about checking continuity. I’d also make sure that your engine ground network is solid. I wouldn’t use MasterPro or any of that bottom shelf crap for ignition parts. If not Delco, then Blue Streak or BWD. I’ve had good luck with both. Maybe Delphi, but I’ve never tried their stuff.

What’s almost certainly causing it is a ridiculous amount of resistance somewhere. A heavily oxidized cap and rotor, particularly aluminum ones, can cause that, you replaced those. Bad plug wires can do that, you replaced those.

After checking the above, I would try removing and testing your ignition coil at the parts store just because they can do weird things and kill things they shouldn’t be able to.

 

[Matt69olds]

What kind of coil are you using? Unfortunately, I have seen this kind of failure a few times, and twice on my own cars. They make a low resistance rotor button, in addition to the factory resistor style.

https://documents.holley.com/84111.pdf


Years ago, I took my oldest stepdaughter and sister in law on Power Tour. We were driving my 87 Cutlass, 455 powered. I had packed spare belts, water pump, anything I thought I might need that parts stores weren’t likely to stock. Of course, the one thing I didn’t pack was a spare distributor cap and coil!!!

 

[MrMarty51]

High resistance down the line from the coil.
Plugs or plug wires.

 

[TyTexan]

So I've checked all the grounds and everything tests fine. When I installed the coil I used both the ground strap and ground wire installed per instructions. All the grounding appears to be good. One coil was a cheapo master pro, one was a blue streak and one was a NAPA special. So I'm pretty sure the brand doesn't have anything to do with it.

Downstream resistance in the plugs or wires are eliminated with the new plugs and wires. It sure could be a control module, or pickup coil. For either of those, I will need to remove the distributor anyway and when it is out, stabbing a new one in would be just as much work. With a control module around $40 and another coil at $40 or so I'm halfway to a MSD distributor for stock application.

I really want, for education's sake, to replace the module and see if that is indeed what is causing my problems...but I'd hate to do all that, and find I still have a problem and end up replacing the whole thing anyway...