My kingdom! My kingdom! My kingdom for an HEI module that will last
 

I have solved all the issues with my HEI, but have yet to find a module that will last. I thought I had it licked by buying the most expensive one available from the parts store, it lasted 10 months (and I don't drive my truck THAT much). At least it comes with a lifetime warranty and I got a new one and I now always carry a spare in the glovebox, but it is a total PITA to have it die in traffic and once I get to safe location pop the hood and replace it. This last time some kind and helpful construction workers nearby helped me push the truck to safety.

And yes, I use the goo on the bottom of the module. With this last one when I got home I cleaned off the dialectric goo included and replaced it with heat transfer paste used for computer processor chips. Hopefully that will help this one last longer.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Yes, my first module lasted nearly 10 years. Then they just go out without any warning.

Last ignition module went south on me back in November of last year as I was going to work. Coasted over to an empty lot and had it changed out in about 25 minutes. I allways carry several spares in my glove box as well. So far I have been using the Accel brand.

I have read on here from several on the forum who say the original ones from GM last a long time. Maybe time to hit up the salvage yards.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

If the truck was converted from points to HEI, was the resistance wire replaced with at least a 12ga wire to the BAT terminal on the HEI coil from the fuse block? I think the original wire for points is yellow, this wire is too small and will cause premature failure of the ignition module in the HEI distributor.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Original GM just might be the way to go. I got a mid-Seventies GM HEI back in the early Eighties and it's still working (knock wood). Got a spare in the glovebox just in case, though.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

The other problem is they do not like too much voltage either. If you have an older style alternator with an external regulator they can produce in excess of 14 volts when the battery is drained.

GM updated the alternators when the HEI came out so use something newer that has an internal regulator and keeps voltages below 14.5.

Someone else could chime in and verify this.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

The truck has a new engine harness built without a resistance wire specifically for HEI.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Heat and grounding issues can wipe out HEI modules early. Make sure you are using heat sink compound on the module. Clean the bottom side of the hold down clamp and add a ground strap to the hold down bolt that goes to a vehicle ground. I would think that would help quite a bit with you module issues.

At least that's where I'd start!:mm:

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

I would think an ignition coil that is drawing too much current (resistance too low) would kill HEI modules pretty quick.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

In my experience, the rotors would burn through due to ancient spark plugs before the module would fry. Of course that's when they were only a few years in the field.

A question for the OP- do you have the sheet metal ground strap that completes the 3rd leg of the primary wires in the coil? I've seen where they were left out, and module life was quite short. Or maybe the connector to the coil primary side has a weak or corroded connection. Modules are generally pretty robust. I have the same module in my Mallory HEI that I bought in y2k. The distributor was originally in the 305 SBC I built and put in my '68 Skylark. I put a Buick engine back in it a few years ago, and put that distributor in my truck. It's over 18 years old and has close to 100k miles on it.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

All the wiring in and around the coil are in great shape. Other than the housing and the shaft, pretty much everything in the distributor is relatively new.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

put a msd 6al in and eliminate the module any halfway decent distrubitor will work fine after that and should last for years

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

This for sure! Haha

As BigDav said, the coil could be layer shorting, knocking out the modules.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Make sure the ground strap is in the cap bolted to the coil. They get left out on distributor cap replacement sometimes and will burn out modules.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

I'm really surprised so many people have problems with the HEI module. I have had HEI dist. in many cars and boats over the years and have never had one fail. I have a no name one in my truck right now, has been in for over 3 years and still working fine.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Years ago a Chevrolet parts counter man told me the HEI's on new Chevys were going out after about 60,000 miles. Mine went 55,000, so I bought 2 and kept one in the glove box for a spare. I never needed the spare, and sold it with the truck years later.
Russ

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

not just any old goo either.

mine went kaput. i scraped off all the grease I could fined to put the new one in and it Dies about 10 months later too. but replaced it with another one and it lasted 6 years until I sold the car.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Does the "new engine harness" still have an "R" terminal connection at the starter solenoid? There is the possibility of a high voltage spike from Back-EMF when the power is removed from the "S" terminal when the engine fires.

What plug gap are you using?

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

I would suggest checking the terminal tension on the connectors that plug into the module. Unplug the connectors and check each one using a male spade connector to plug into each terminal. They should have some drag on them when you remove them. It could be that your modules never really failed. It just fixed itself temporarily when you plugged the new one in. Seen it many times! ;)

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

As mentioned above, high and low voltage will both kill modules. Running your keyed 12 volt source from your fuse panel is good, but not foolproof. That source can still experience fluctuations, depending on the condition of your trucks wiring harness. I recommend using the keyed 12 volt source from your fuse panel to operate a relay. The relay doesn't care about high or low voltage (extreme high voltage/amperage excepted). That way, you can run your clean 12 volt source directly to the HEI from the battery. I have found this to greatly increase the longevity of HEI modules.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

The modules are very difficult to unplug so the connections seem tight, but checking them individually couldn't hurt. Both the under the cap harness and the pickup coil are brand new so the plugs should all be in great shape.

The only time I tried a new coil recently it ran worse, much worse. Still running the coil that was in the HEI when I got it from a friend off a junk engine. Other than the body of the distributor and the shaft, it is the only original part left. Cap, rotor, harness, pickup coil, weights, springs, bushings, external wiring, spark plug wires, vacuum advance and module are all new or newish. Ran fantastic for quite a while, problems just cropped up last year.

If it was frying modules due to starter feedback or fluctuating voltage, wouldn't that fry the modules at start up or soon thereafter? This only seems to happen when I am happily tooling down the street. Temps outside being hot or cold seem to make no difference (though I don't drive it in the winter).

I'll pull the cap off an examine the coil and it's connections when I get a chance, probably not until next week as it is hot and miserable out all this week.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Damage can happen over time if it is getting surges or excessive voltage, not always fry right away. Interesting your new coil made the engine run bad, I wonder what was going on with that. I was reading your first post above, do you think the previous module that failed had the wrong type of heat sink compound goo? Do you have an alternator with internal or external regulator?

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Yep... need to use heat sink grease/compound and not dielectric grease.

I've used many HEI's. Stock and aftermarket and have only had one ignition module go bad, and that was my fault. Been using them for many, many years.

Gary

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

As I said above, I have used heat transfer compound, not dielectric grease.

I would assume the new coil I got was no good, tends to make one wary of new parts when "new" ones are less reliable than the old originals. I could try a different brand of coil but I'm not sure that would make a lick of difference. Anyone I've talked to who has installed an HEI in the past five years, they too have had a hard time finding a reliable module.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

I converted to a pointless distributor many years ago when I was still running my 250 motor. I continued with a pointless distributor when I converted to a 350. My mechanic did all of this for me. I kept getting stranded with this HEI. It would intermittently quit working. We changed modules and distributors several times and he did other things to it and I still had problems. The last time I had a problem he took the distributor out and took it back to NAPA. He was buying a remanufactured distributor and this time he got a new one. Never had a lick of problems with the new one. Several remanufactured ones left me stranded.

Re: My kingdom! My kingdom! My kingdom for an HEI module that will last
 

Forgot to answer earlier, the truck still has the original style charging system with an external voltage regulator and alternator without a built-in regulator.