Thread: Burning out Chevy HEI Ignition modules

Tweet

My S10 had a 305 in it and I never replaced the ingnition module. When I dropped my 350 in I used the same distributor. Within the year I replaced 3. I noticed the old distributor harness & wiring were getting birttle, so I dropped in a new Mallory Distributor in it. Its been 9 months now and last week I had to replace the module that came in the new distributor. The distributor came with the coil & other HP parts. When I replaced the Module I checked the cap. There is no corrostion on the rotor or terminal in the cap, but there is a brownish black sout inside the cap and on the rotor. What is causing this problem? And are they related. Somebody told me heat kills the module but what causes the suot. Stephen Roy new E-mail address srsv8dime@bellsouth.net Thank you.

Are you puting the dielectric compound between the module and the distributor? This is used as a heat sink.

Originally Posted by lucforce

Are you puting the dielectric compound between the module and the distributor? This is used as a heat sink.

Yes I have been putting dielectric grease under the module.

Originally Posted by DennyW

You have to also make sure the pickup windings has the correct resistance, or it will over load the module. (to many mili-amps). And, do not use the cheap modules, they are different.

The module that went bad was a Mallory HP , The replacement module is a cheap Wells. On the pickup windings are you checking the coil or the pickup coil. And are you using a ohm meter to measure this. Also what makes the cheaper unit not good? Not enough saturation!

Check the alternator output. Too many volts will fry 'em quick.

Originally Posted by R Pope

Check the alternator output. Too many volts will fry 'em quick.

Its putting out about 16volts acorrding to my volt guage, I think thats about where the out put sould be, or do you think it should be closer to 14? And when you measure it are you measuring at the altenator, it should be the same. Thanks for all your inputs to help me get to the bottom of this problem. Also what about the brownish film inside the disturator cap. is that a sign of arking or too high voltage? Steve

I know this may sound stupid,but make certain you've got good grounds,block to frame,and frame to battery. At 16v you are definitely over charging. Hank

The voltage should be the same anywhere in the system that isn't on a resisted wire. Check for high amperage too, though 16 volts is too high. The comment about the battery is a good point, an alternator will screw up its charge rate if the battery is going away.

been reading with you guys and i agree that high volts is not good for the unit, i fried one at 15.7, way to hot. i know that the charging system should be between 13.8-14.2 depending on the ambiant temp. and that should only change it slightly

Like others have already said....16 volts is too high. Have the alternator and the charging system checked out, before you toast all things electrical. My one wire alt went berzerk a few years back on a run to Lou'ville, fried the internal regulator, blew the battery and scorched a lot of wiring. It was charging at 18 for just a few moments before I could get it shut down, which was already too late. Didn't damage the HEI, but everything else was ugly.

I did check the altinater out put, and it is puting out 14.5 volts I also bought a new mod. from Jegs to put in to get the wells unit out of there. I also bought a ground strap and will be putting it on. I think I am going to keep the cheap wells unit as a just in case! I will let you guys know if any other problem comes of this. I eally thank everybody's imput. Thanks Steve. New e-mail address srsv8dime@bellsouth.net

Originally Posted by R Pope

. Check for high amperage too, though 16 volts is too high.

i personally dont like telling people to check for amperage unless i know they know what they're doing... too many times have i asked someone to check amperage and they dont hook it up in series, and next thing you know they blew my fuse in my meter and fry some electrical in the vehiclel.

Originally Posted by Stephen Roy

. I think I am going to keep the cheap wells unit as a just in case!

good idea.... kinda like i used to keep a spare set of points in my galaxie.... fords always fuse points which can really be a problem

Originally Posted by DennyW

If he's pumping 16 volts, you can count on the amperage not being correct.

((fords always fuse points which can really be a problem)). Only true if the system is not set up correctly.

yup like using too hot of a coil and cheap points... which is what a lot of people do... including me until i upgraded to electronic ignitions one by one on my cars... i've only got one that still runs points and its one i stuck an engine i found laying around in and am planning on selling....

and yes of course amperage wont be correct with 16 volts because the resistances aren't changing.... but incorectly testing for amperage is a good way to let the smoke out of your wiring