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Discussion Starter · #1 ·
Hi, I've been having really bad luck with the modules in my HEI. I've had at least 3 fail this year. I apply the grease underneath so that's not an issue. I'm running several ground straps, involving the engine, frame, and body. I've even tried a different distributor. A couple of the modules were GM pieces and the others were from Autozone.

I seem to get the same exact scenario. A 30 minute drive, turn off the car for a little bit, and then no restart. The modules have never failed while driving.

I've recently installed a points distributor, but I'm not crazy about it. The engine runs so much better with the HEI. Maybe the points distributor has it's own problems, it should run better than it does. It has an all new tune up, points gap and dwell are dead on.

I would love to return to the HEI, but I'm tiring of switching out modules.

One last thing, just a theory. I have a one wire alternator. Could I possibly getting a voltage spike and that's what is frying the modules?

Thanks for all your time!
 

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If its the alternator it would fry the module whilst driving.

Are you buyin the modules from the same place, do they have a bad batch?

When you exchange them what are they saying is the problem?

Thats a lot of modules to replace in a short period of time.
 

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I had a couple of stock ones fail but it was when my car first hit the road and I had starting problems. I was using jumper leads and I think we spiked the module. Once starting problems were solved I also fitted a Mallory HEI and it has been in there for over five years with no problems ever. I don't know if the GM ones are a bit touchy or not but the Mallory has been faultless.
Cheers.
 

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Man, that's kinda puzzling, it's got to be something simple causing it though. A long time ago I had a GMC work van that would pull that every few years. Thankfully a parts house guy talked me into buying two when the first one burnt. Every time after that when I burnt one I would buy another always keeping a spare around, in the van.

When you get sick of the points try running a mag. Ha!
Good luck.
 

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Do you have a full 12 volts to the distributor using 12 gauge wire? I'm sure you have checked this, but if you are using the original harness with the resistor, it won't work properly. Like I said, I'm sure you have checked these things but first things first. When you said you were going back and forth between an HEI and a point distributor, it makes me think.
 

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Coil part number, and internal ground strap.

I recall there were at least two different coil part numbers, with different color wires to identify them. I presume it was to pair up with different series modules. Also, some HEIs came with peculiar internal hard ground straps that fastened to the coil frame.

Hope you find the problem.
 
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There are four reasons for HEI module failure, only one of them is the all out winner of the failure main issue

Lower level issues

"Spiking", is so extremely rare, it just isn't a factor in module failures, and, the system would have had to go well past 50 volts to kill the module by spiking. I could see this happening if there were 4 or 5 batteries connected in series (+ end to - end), not parallel.

Long term high voltages, well past the 14.60 volts HEI systems with good internal regulator alternators run at. If the system was running at 25 to 30 volts for that 30 minute time, yes, the module, and most other stuff in the vehicle, would have blown out, and you would have seen the effect in the light bulbs, in that the filaments would have been vaporized, and impacted the inner side of the bulb glass, making it silver coated.

Moderate

Carbon post installed incorrectly, above the insulator in the cap, raising the brush off the rotor bar. This sets a third gap in the system, radically increasing the load on the ignition coil, which overloads a module to failure. Te other two gaps are set distance, and their resistance is factored into the current the system runs, spark plug gap, and the gap between the firing tip of the rotor, to cap wire terminal. Easily fixed, install a new carbon brush, goes cap, brush (with spring wend up), insulator (with spring protruding through its center hole), coil.

MOST COMMON CAUSE, apprx. 99 percent

IGNITION COIL IN THE CAP. Epoxy filled coils in HEI caps are a heat stove, they do not leach heat out of themselves, as an oil filled coil does, and, this heat leads to "layer shorting", when the coil literally melts the insulation way from the individual layers of primary windings. As the windings touch, the change coil resistance on the primary side radically increases, creating massive load on the HEI, MSD, or other module, to failure. This can be gradual, exponential, or, immediate failure.

I have seen layer shorted HEI coils take a brand new, quality HEI module right out in less than 30 seconds flat.

To properly test both an HEI module, and/or HEI coil, resistance checks are no longer effective, unless both are full on DOA. Both parts will need to be run on an off vehicle run tester, most better auto part stores have them. The "tech" there will most likely want to test the parts for 5 seconds, decree they are good or bad, and let it go. Don't let them do that, let the parts run right up to operating temperatures, as that is where most failures occur, not when cold (you did mention the problem occurs at or near 30 minute operation times).

Do check all grounds, especially at the coil, there are two. First is under the coil, in the form of a buss bar from the coil yoke to cap term GRD, second is the wire out of the coil to one of the coil mounts. HEI in cap coils MUST be grounded. This wire grounds the coil to its yoke, the buss bar from the yoke to the 3 wire connector center terminal on the cap. From the cap, through the terminal, ground continues to the distributor body, with the end of the ground wire being retained to the distributor body with a screw. Any dirty/loose/corroded terminal will increase coil resistance, which can help build coill load, overloading modules to failure.

Check the resistance of the spark plug wires as well, 'rule of thumb' is usually 1,000 ohms per foot of wire length. Wires must be magnetic suppression, spiral, or "magna" core, and 8mm. Resistor plugs are OK, but, critical, spark plug gap should not exceed .045 inch gaps, MAXIMUM.

On the two different coils for large cap HEI, yup, there arte. One is the one to use, fits most applications, .045 plug gaps. The other was a cap that was supposedly to help with emissions control from a larger .060 to .080 plug gap. These large gap coils were used mostly on Olds engines, and, some very few Pontiac, Cadillac left hand rotation distributors, UNTIL it was found the massively giant plug gaps were taking those coils, and HEI modules right out from too much resistance created heat. The factory then issued a FDM to order the effected coils replaced, with the smaller gap coils.

As far as so called "Performance" coils, and their supposedly good massive gaps, NOT. No matter the coil n cap, no matter whom builds it, keep the spark plug gaps down to no more than .045, MAXIMUM. My experience has shown the best thing that can be done with all HEI in cap coils, is to replace it with a remote mounted, oil filled, off cap coil.

Hope this helps

Dave Ray
DAVE's small-body HEI's
 

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Discussion Starter · #8 ·
Thanks so much for the replies! I have to apologize for the heading, "Hawaii", lol. I posted this on my smart phone and I guess it's not very smart.

I'm running a 12 gauge wire from the ignition switch to the coli, no resistor in place. I actually thought I had this issue fixed. I haven't had a module go bad for 2-3 years now. In the last four months I've went through three. Several years ago it was happening pretty often as well. Cruise in season is about over, I'll have some garage time to try and work it out.

Dave Ray, thanks for all the info! I will save it!

Thanks again everyone!
 
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