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electrical question- HEI, BBC and run-on

Discussion in 'The Hokey Ass Message Board' started by praisethelowered, Jul 7, 2005.

  1. praisethelowered
    Joined: Aug 14, 2003
    Posts: 1,103

    praisethelowered
    Member

    I just fired up a truck a few weeks ago that I completely re-wired (EZwire harness- though heavily modified to fit a mid engine coe truck) and the big block chevy motor has all new bolt-ons (carb, HEI dist., one wire alt, starter, etc.).

    Thankfully all seems to be well with the motor, it idles good, runs cool, fired right up and all of that. . . but when I turn of the key and remove it the motor keeps running for 10 seconds or so.

    I can't figure out what would make this happen. It is definitely electrical- not dieseling or anything like that because it keeps running smooth at full idle rpm for those ten seconds then drops off just like the key was removed . . . just ten seconds late.

    Has anyone had a similar experience and figured it out?
     
  2. theodore
    Joined: Nov 28, 2003
    Posts: 180

    theodore
    Member

    It may be feedback from your alternator, if you put in a diode, it should fix it....
     
  3. You are getting feedback through the alternator, you need to put a diode in the line so power can only flow one way. This is a common problem when people put on a MSD box or similar set-up. I don't have details in front of me now, but the diode will fix the problem. Try looking at the MSD website, it may have an explanation and the diode to get and where to put it.
     
  4. praisethelowered
    Joined: Aug 14, 2003
    Posts: 1,103

    praisethelowered
    Member

    thanks, i'll check into that. . if anybody know where to get the right diode please let me know.

    but. . . .
    i think
    my atlernator output wire doesn't have a path to the ignition wire when the starter switch contact is broken. . so i don't see how it could be feeding it?

    and I don't have a msd box either. . .
     

  5. nobux
    Joined: Oct 19, 2002
    Posts: 643

    nobux
    Member

    Basically, you need a "one-way-diode". I think I got the last one I needed at Radio Shack. Just explain to them thst you need a diode to let current flow one way, but not the other. Your alternator needs an ignition "trigger" to energize the field. Once the field is energized, it stays energized until the engine stops spinning it. Without the diode, current back feeds through the ignition trigger wire and keeps the HEI energized.
     
  6. enjenjo
    Joined: Mar 2, 2001
    Posts: 2,551

    enjenjo
    Member
    from swanton oh

    Unplug your electric fan, and see if that changes it. If it does, put a relay in the fan circuit.
     
  7. praisethelowered
    Joined: Aug 14, 2003
    Posts: 1,103

    praisethelowered
    Member

    yeah but I have a one-wire alternator. . . with no trigger wire. . . right? I am still confused.
     
  8. nobux
    Joined: Oct 19, 2002
    Posts: 643

    nobux
    Member

    It HAS to be in the alternator. Try starting the truck with the alt. wire disconnected. It BETTER shut right off. With a one wire alt., you'll probably have to run a relay on the wire to the alternator.
     
  9. praisethelowered
    Joined: Aug 14, 2003
    Posts: 1,103

    praisethelowered
    Member

    thanks guys that's enought to give me a few experiments to try tomorrow.

    start it without the alternator hooked up? . .why didn't i think of that? i'll check the fan too. . .
     
  10. nobux
    Joined: Oct 19, 2002
    Posts: 643

    nobux
    Member

    I was looking back at some of the old posts in my folder. Praisethelowered, what ended up being the problem? Curiosity got the better of me, and I'd like to know.

    Karl
     
  11. Big Pete
    Joined: Aug 7, 2005
    Posts: 364

    Big Pete
    Member

    If you have an electric fan cooling system It's the fan, do what he said and disconnect the fan, see if problem clears.......... let us know.......
     

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