Gm ignition module burnouts

Could you guys explain what might be knocking out my module inside my Hei vacuum advance distributor? Ive replaced about 5 the last few days. These were all used because Im not going to put in a new one until I find out why they are going out. The distributor is , I dont know what year model ! but I found out that my 85 truck is different than this one. The one Im working on is 1 wire going to my ignition switch ( I hooked it directly to key switch) the module and dist. are older hei tan my 85 truck because I was taking the mod out of the truck and it has 3 prongs on 1 side and 2 on other. Do I need a resister in the hot wire to switch?


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Make sure you have 12v at b+ while cranking, you must use the white grease under the module for heat sink, check the center grd spade in the cap, make sure it's fastened under the coil, and also check the pickup coil wires to the module for rubbing or breaks HTH Forgot- no resistor!

Thanks guys., Changed everything in distributor , still wouldnt crank, relaced it with old one I had , no crank , about to give up but tried one more cap with coil and its running. I was taking parts of of my 82 Chevy and trying them in the distributor , and new they were running and good but they never would crank it, then I would take them out put them back in the 82 and fire it up. So I new the parts were good. When I changed the whole dist. body and didnt crank ! well ,,, For some strange reoson I changed the cap and coil again and it worked . Why? I guess somewhere in the confusion I missed something. This is a 350 in a 91 Samurai jeep . Thanks it worked

1 - Coil was starting to layer short, overloading the modules to failure.

2 - Rotor has burned through to the mechanical advance under it, overllading the coil and/or modules to failure.

3 - Carbon brush damaged and/or incorrectly installed in the cap, overloading modules to failure.

4 - Bad ground between coil and yoke, small black wire from the coil. Coil yoke to bus bar ground bad, dirty, causing coils and/or modules to overload and fail. Bad coil ground at distributor body will also cause coil/module overloading and failure.

Low voltage to the dist WILL NOT cause failures in an HEI. Resisted input sources have been maligned as the failure causes, but no, they aren't. OVERVVOLTING, as in a stuck regulator producing upwards of 18 volts will kill the coil/module in one quick hurry.

The 5 wire HEI module functions EXACTLY the same as a 4 prong module, but has the 5th wire input for a stand alone knock sensor used on early non-fully computerized systems. If you had the small processor, sensor and wiring for the knock sensor, you could install it and have detonation protection. A regular 4 prong HEI module will interchange into that body, and eliminate the use of the knock sensor systems.

Doc here,

Also An Alternator with VERY bad diodes will cause this..Infusion of AC into the module will kill it..Pull the wires, put in another good module and test it ..see if it lasts..(don't forget your not charging and let the battery go dead..)

Water or other organic lifeforms in the coil well..

A bad or Shorted Tach, will reek havoc..If you have one, disconnect it..

Wires that short on advance...

Major crossfires at the cap..inducing RFI sparks into the module..

That's about I can think of..

Doc

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Ignitionman is right on about high voltage! I was driving along 4 days ago when the volt meter started pegging on 18. The module burned up within 1/4 mile!

I have found that the most common cause of ignition module failure, across all brands, is a faulty secondary ignition system. Basically, there is an open in the secondary circuit or a cross fire occuring. There are theories as to what the actual cause of the module frying is, but the root cause is the secondary ignition system. Coil, cap, rotor, wires, plugs. Some say that an induced inverse current is produced thereby giving the module a reverse polarity high voltage surge (same as bad diodes or faulty regulator or crossfire hitting the module inside the cap) and some say that the coil draws too much current through the module when producing maximum voltage to try to jump an open or large gap in the secondary ignition (like a shorted coil). I would check the aforementioned parts for any and I mean any defects, or just replace them all as they cost less than a handfull of quality modules.

Most common cause of module failure is still overheating of the in cap coil, and its layer shorting, causing increased resistance the coil trigger side of the module cannot handle. This can be from overvolting, rotor to carbon post issues, bad coil grounding, but mostly from the heat environment the coil lives in, in the cap.

I do this stuff EVERY day. I see all kinds of wierd, strange, voodoo, outer space and just plain levitating at the nuthouse theories, lots of bogus and wrong tech from stuff like magazine whizzbangs, but its the failed/failing coil in one of those nightmares that just about every time, takes the module right out.