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Dumbfounded by TBI prob--please help

Discussion in 'The Injection Section' started by Madbomber88, Jan 6, 2007.

  1. Madbomber88

    Madbomber88 1/2 ton status

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    Ok, just finished installing a TBI conversion on my 72 K20 using a new painless harness and donor everything else.

    Here's the problem...
    It will start and run fine, but will not turn off. Everything else turns off (radio, heater, etc...) when I turn the ignition on, but the truck keeps on running. THe pink/black wire from the computer that is labeled "connect to ignition" is what powers the computer in the harness. I have connected that to a million different feeds that are only hot on start and run. But when you connect it to the pink wire, it fires up and runs, but stays hot when you shut it off. What does this mean?
     
  2. Jason4x4

    Jason4x4 1/2 ton status

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    I just did this swap on my 83 with the painless, and I am going through my book, and the only thing I can think of is, check power on your coil, make sure it is only power with the key on, and the wires going to the starter, check and make sure they are hooked up correctly, the bigger one goes to the positive cable on the starter, but i'm thinking you have the small one hooked up wrong, the small wire on the starter goes to the same terminal as the crank wire from the ignition switch, i'm thinking you have it on the other terminal, if it is not on the start side, I think it would do what you are saying. The only thing that it does is tells the computer that you are starting to crank, it is basically a crank sensor. check that and let me know.
     
  3. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Sounds like a wiring issue, go back through and make sure ALL your connection are correct.
     
  4. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Something is definitely up with your ignition wiring. Your coil shouldn't be getting any power after you turn the ignition off, which should kill the engine immediately, regardless of what the ECM is doing. Along with that problem, your ECM is still getting power to it's ignition input pin, to keep firing the injectors etc after the key is off.

    So, go and probe the thick red wire that goes into the ignition coil, and find out why it doesn't shut off when the ignition switch is off, and also probe pin A6 on your ECM.

    If you are sure you installed these two wires to the correct posts coming off your ignition switch, then you need to confirm that the switch itself is good.
     
  5. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    Did you change the wiring to the alternator by chance? Sounds like the alternator maybe backfeeding the pink wire to the ECM. Simple enough to check by unplugging the alternator and see if the problem goes away.
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Good thinking!
     
  7. Blazin'4x4

    Blazin'4x4 1/2 ton status

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    Been goin through all the projection threads and it seems like every ones problems occur from mis wiring. I found my multimeter is my new best friend on my tbi. Poke and prod everything. Process of elimination. Where did you run your return line to? Heard its not a good idea to detach tank vents to run returns.
     

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