HEI conversion is turning into a train wreck

Discussion in 'Electrical and Ignition' started by TylerW, Aug 5, 2018.

  1. TylerW

    TylerW Well-Known Member

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    Hey guys:

    Hopefully I can ease this one in here...I have a vehicle that was originally Lean Burn equipped. I had all the hard parts on hand to convert it to an HEI, so I did. Since then, I've had ongoing issues getting it to run and to run right.

    It worked fine when I got it together. About 500 miles later, it lost spark after sitting about 4 hours. Tow home, try it several times and an hour later it starts and runs fine and hasn't repeated that episode just using it around the house.

    Yesterday I decided to replace the junkyard coil and pickup coil(in the distributor) with good quality new stuff I had. Took it for a drive today on my 5 mile test loop and picked up a misfire under load about halfway through which got worse the further I went. Felt like ALL the spark was randomly falling out, not just one cylinder. Further testing at home revealed that the misfire goes away when the engine cools down. Plugs, wires, cap, rotor are all recent and in good shape. Timing is 8 degrees BTDC with advance unhooked and mark is rock-steady. Pickup coil air-gap is set to .008 per the FSM.

    I want to post my setup in case I have done something glaringly wrong to cause this:

    1979 318 vacuum distributor with new pickup and vacuum advance . Wells HEI module mounted on the passenger inner fender, on a heat sink and grounded to the chassis. Ford TFI coil mounted on the inner fender also and connected to the distributor with a good-quality 8mm 36" coil wire. The HEI module and TFI coil are both powered through a Ford cooling fan relay from a Crown Vic. The trigger for the relay was tapped off the key-on power to the original LB system, and the 12v run circuit for the relay is powered by another, separate 12V "battery voltage" circuit with a 30A fuse inline. Feel free to suggest improvements or point out something I did wrong. Thanks!
     
  2. brian6pac

    brian6pac Well-Known Member

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    I always try to keep the coil wire as short as possible, don't think that's your problem, just saying. I put my coil inside the car and a gromit in the fire wall for the wire. Keeps the coil cool and the wire short.
     
  3. Bulldozer

    Bulldozer Well-Known Member

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    • Agree Agree x 1
    • jos51700

      jos51700 Well-Known Member

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      How are you verifying that it's losing spark and not fuel?
       
    • jas0162

      jas0162 Well-Known Member

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      Could the relay be crapping out? I have a hei module screwed down on my passenger inner fender too, it has ran great for several years. I just use the stock type coil and wiring with the ballast bypassed. I did run a ground wire from the module and voltage regulator to the battery just to be sure, I know bad grounds will kill the mopar box, not sure about the hei
       
    • Abodybomber

      Abodybomber Breaking street machines , since 1983.....:)

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      Talk to Greg ,aka "Trailbeast'.... save stress and time....
       
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      • Dana67Dart

        Dana67Dart Most undignified way to get to Colorado!

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        So let me see if I got this right... You have a GM style distributor, a Ford coil and a Mopar car. And you wonder why it doesn't run right? :lol:

        I know I'm no help!

        My bad just googled a Wells HEI. Scratch the GM style dist.
         
      • TrailBeast

        TrailBeast Slightly Twisted Member

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        If you are sure it's a spark problem, this is how I would go about diagnosing this.

        1. Distr pickup gap
        2. Verify a good ground for the module
        3. Check wiring for a loose contact or crimp
        4. If using a stock pigtail connector for the distributor to module crimp it tighter ( or even remove it)
        Twice so far I have seen this pigtail loose connection when they got warm with the engine.

        If I still had the problem it would get a different module.

        One thing to note about the module ground is this.
        Just because it's touching grounded metal does not mean the inner circuitry is getting the ground it needs.
        Try tightening your mounting screws, or use machine bolts to hold it down.
        Those eyelets on the module need to be pressed down to be in contact with the module backing metal r it's likely not going to have a good enough ground.

        ALL of the problems I have seen arise with HEI were either a bad power supply or not a good enough ground.
         
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        • fjr

          fjr Well-Known Member

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          The HEI conversion is very straightforward and reliable. I just upgraded my 65 Barracuda in June and it works perfectly but I used a GM HEI module and ran a 12g ground wire from the battery to the module. See HEI Ignition Upgrade.
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          thanbk you for posting that link. I now have an understanding of the HEI conversion.

          TylerW did you use thermal paste between your heat sinks and the modules?