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Technical GM hei goes bad

Discussion in 'The Hokey Ass Message Board' started by trollst, Jul 23, 2016.

  1. trollst
    Joined: Jan 27, 2012
    Posts: 2,058


    So, about ten years ago built a friend a 36 chev pickup, 350-350 combo, I wired it, been an absolutely great truck all these years. However, he has been through at least five ignition modules in ten years, all have failed when the truck has been parked in his garage, (or the last time he parked it).
    In comparison, my 36 ford pickup, 327-350 combo, has never fried a module in 17 years on the road.
    Any of you got any ideas why this happens? Both have stock hei distributors, both trucks wired the same, both put out 14.5 volts steady, no fluctuations, good steady power.
    Really just trying to understand why this happens, thought some of you may know.
  2. choptop40
    Joined: Dec 23, 2009
    Posts: 3,937


    Sometimes I think if you leave the key 2 cents
  3. I had similar issue, added a better ground from HEI to chassis, problem went away
    scrap metal 48 likes this.
  4. xracer40
    Joined: Jun 20, 2010
    Posts: 308


    My guess would be it is ground related.

  5. under the cap where the coil is,are 4 screws that hold it in place.One of these screws has a ground strap that goes to the 3 prong plug. Make sure that the coil screw and strap are completely clean.
    scrap metal 48 likes this.
  6. chopolds
    Joined: Oct 22, 2001
    Posts: 5,956

    from howell, nj
    1. Kustom Painters

    Also, VERY important: use AC Delco parts! Aftermarkets stuff WILL fail much earlier.
    bryan6902 likes this.
  7. X2 on making sure the ground strap is properly installed.
  8. trollst
    Joined: Jan 27, 2012
    Posts: 2,058


    Thanks, there are grounds everywhere, something I learned early when I started wiring cars, maybe, though, the ground on the engine may not be as good as it could be. I'll get him to check.
  9. missysdad1
    Joined: Dec 9, 2008
    Posts: 3,016


    The ground being referred to is inside the distributor.

    Also, I've learned to carry spares for all the internal parts to my HEI, including the coil which can - and does! - fail unexpectedly.

    Good luck!
    stillrunners and i.rant like this.
  10. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,226

    Da Tinman

    Make sure to use the heat sink grease. That white stuff under the module is there for a reason other than getting all over your hands.
    sunbeam and thirtytwo like this.
  11. Black Panther
    Joined: Jan 6, 2010
    Posts: 1,767

    Black Panther
    from SoCal

    X2 on the above...
  12. Here is a picture of the often missing ground strap. End of the strap goes into the middle hole on the HEI wire plug. I stole the picture off the internet (from a Jeep forum, no less) but it is the best one I could find. :)

    Attached Files:

  13. 6-bangertim
    Joined: Oct 3, 2011
    Posts: 400

    from California

    CHECK the pick-up for resistance with an ohm meter - it should be in the 500-1500 ohm range. A pick-up outside of that range WILL shorten module life.

    USE an AC-DELCO module! I have installed FIVE modules in a V-6 S-10, in 19 years and 215,000 miles. NONE of the aftermarkets lasted as long as the factory module... it went 60k!

    Good Luck, let us know what you found out. I really like the HEI, easy to trouble shoot with a test light and a multimeter. Tim
  14. HEAT SINK Grease! DO NOT use Dielectric grease!
    arkiehotrods likes this.
  15. arkiehotrods
    Joined: Mar 9, 2006
    Posts: 6,477


  16. trollst
    Joined: Jan 27, 2012
    Posts: 2,058


    He says it all looks good, he's used aftermarket modules in the past, found an old hei distributor and used the ac delco module out of it, says it's all good now, we'll see, time will tell. Thank you much guys, LeRoy.
  17. I'm going with heat sink grease too.
    Joined: Jun 15, 2006
    Posts: 3,385


    Some interesting comments. Delco no longer make any products and reboxes or sources all parts today. The new modules are no where near the old modules with all the protection circuits in them. His car is more that likely fixed if he found a old style module,,,,,,
    CornfieldPerformance likes this.
  19. another vote for the heat sink grease, it is often over looked.
  20. bryan6902
    Joined: May 5, 2008
    Posts: 1,137


    If what Delco sells these days is junk then go harvest at the local yard.. GM made plenty of HEIs for everything and I think the modules and coils are very interchangeable. I think I have 3-4 coils and modules that I have kept for this reason. Working at a parts store helped re-enforce that the new stuff is trash.
  21. 283john
    Joined: Nov 17, 2008
    Posts: 824


    I have a v8 s-10 pickup with HEI. A previous owner had butchered the wiring to rear lights. It got to the point where it would blow the tail-light fuse about once a week and...for some would cook the ignition module about once every two months. Found a good unmolested wiring harness from the mid-frame plug all the way to the light sockets to replace it all with. Fixed both problems.
  22. Galaxie390
    Joined: Nov 7, 2012
    Posts: 13


    Ha! Had this happen to me today. The spade connectors in the distributor had lost their tension. Third module in a short period of time. I tightened up the connectors by squeezing them slightly, then put a module back in that I thought had failed (engine died, no spark) and it fired right up and idled for 20 minutes. Lots of heat cycles, even these hei distributors are getting old.

    Posted using the Full Custom H.A.M.B. App!
  23. samurai mike
    Joined: Feb 24, 2009
    Posts: 503

    samurai mike

    this has been my experience
  24. Agree on needing three things mentioned:
    1. Good ground
    2. Electrical wires with solid connections
    3. Heat sink grease under the module.

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