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Injectors stay on?

Discussion in 'The Garage' started by AKBurb, Jun 9, 2006.

  1. AKBurb

    AKBurb Newbie

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    Eagle River Alaska
    I have a 1991 GMC Suburban 3/4ton with the 350 and factory TBI. mods include Edelbrock TBI intake, Mallory 6 ignition, and an MSD Blaster series replacement coil (the weird 4 pin). a little bit ago when I replaced my intake manifold, we noticed an odd problem when trying to redo the timing. after a failed start attempt, the injectors stayed ON when we stopped cranking and left the key in the run position. it did this twice after several start attempts, and after tracing obvious wires for a short, we noticed it wasnt doing it anymore thinking it related to twisting on the distributor. biiig mistake. now it seems to be doing it after EVERY failed start attempt, and is getting highly annoying. It is both spraying a steady spray, not pulsing (or noticable pulsing anyoo).
    Also, the coil itself is acting a little funny during this. it is making an annoying buzzing sound, varied tone, that repeats, kind of like a computer error beep. it is a long steady tone followed by a lower short tone, with another lower short tone, to repeat with the long tone. it doesnt appear random, yet it isnt a constant single tone. overall very odd. this happens at the same time as the injectors doing their spray.
    It SEEMS to me that the computer is sending the injectors and the ignition system a run signal after any failed start, but beyond that I am stumped. any ideas for trouble shooting or any fixes in mind? thanks in advance!
     
  2. jarheadk5

    jarheadk5 1/2 ton status

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    Quickest way to see if it's the computer is to swap a known good one in, and see if the symptoms repeat. Failing that... download WinALDL, build or buy an interface cable, and run it to find out what your computer is thinking.
     
  3. readymix

    readymix 3/4 ton status

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    FYI. One side of the injectors is always hot.
    The other side is a pulsed "ground" which causes the injectors to fire.

    Not sure if you knew that but I would hate to see you chase the wrong symptoms
     
  4. sled_dog

    sled_dog 1 ton status

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    did you install everything at the same time? What did you tie into for the Mallory Ignition? I'm wondering if you inadvertently tapped into the crank position sensor and the aftermarket ignition isn't storing enough power in its capacitors to make the computer thing its running... If by some chance the ignition box is puting off a good enough power spike it could be a false signal to the ECM. Thats a big time shot in the dark and just the first thing that popped into my head.

    ALways trace what you've touched. Look at things you removed and installed(which with a TBI and an intake swap, thats a lot of stuff). Most of the major sensors in a TBI system are mounted right there on the intake manifold(MAP, ECT, CKP, and Ignition).
     

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