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Thread: truck runs for 30 sec then dies help!!!!!!

  1. #1
    Fuel Injected!
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    truck runs for 30 sec then dies help!!!!!!

    truck runs for 30 sec then dies. i have the 7747 pcm.tried oil pressure switch didnt work. but i dont have a hot fuel mod. injectors spray on start up then just stop. check all my grounds and double checked wiring. could the hot fuel mod be causing this problem? i am also running my stock 2.5l fuel pump relay that has gray for the fuel pump test that is ran to b2 fuel pump in put
    Last edited by lilhupper; 02-28-2013 at 11:42 PM.

  2. #2
    EFI GearHead ! EagleMark's Avatar
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    It's not the oil pressure switch, it is redundant and you don't even need it.

    But if oil pressure switch is bad it will not continue to provide power to fuel pump relay if fuel pump relay fails. Check the relay and see if the power to fuel pump stops at same time?

    There's a green wire to the relay that comes from the ECM that turns it on. But power comes from elsewhere, goes through relay when turned on by green wire from ECM and sends power to fuel pump.

    Relay is on firewall and looks like picture below, wiring is simalar but differant relay.

    HTH!
    Attached Images Attached Images

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  3. #3
    Fuel Injected!
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    yes the green wire goes out before the it dies

  4. #4
    EFI GearHead ! EagleMark's Avatar
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    If you hook 12 volt power up to the test/prime terminal and it runs? Then it would have to be the ECM? If wiring is correct. Is it consistent 30 seconds each time? Will it start after the stall?

    Here's a link to diagram.
    http://www.gearhead-efi.com/Fuel-Inj...8&d=1331599730

    Do you have one of these on your harness?
    Attached Images Attached Images

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  5. #5
    Fuel Injected!
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    yes its a consistant 30 sec and will fire after stall. no i dont have that.

  6. #6
    Fuel Injected!
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    puting a constant power to the test wire doesnt help motor still runs for 30 sec then dies. does anyone know what the fuel mod does. im going to go over the wire harness to night and make sure all wires and hooked up correctly and none of them are pinched.

  7. #7
    EFI GearHead ! EagleMark's Avatar
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    What fuel mod? The Fuel module that came on some HD trucks? It runs the fuel pump for 20 seconds after key off.

    I think you have some wires wrong and it's tripping the relay? Or wrong relay? You said it was from a 2.5L?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  8. #8
    Fuel Injected!
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    yes fuel pump relay are off the 2.5 tbi the wiring diagram has a hot fuel mod that i dont have. the fuel pump is tripping ill try puting the 350 relay on too

  9. #9
    EFI GearHead ! EagleMark's Avatar
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    Might have lost the B2 signal when removing the Fuel module? Something is wrong with wiring?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  10. #10
    Fuel Injected!
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    does this computor need a knock sensor? mine is not hooked up

  11. #11
    EFI GearHead ! EagleMark's Avatar
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    It will run fine without.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  12. #12
    Fuel Injected!
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    injectors are not palsing

  13. #13
    Fuel Injected!
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    i get 2 or 3 sprays of the injectors then motor fires and injectors stop and motor dies

  14. #14
    Fuel Injected! jim_in_dorris's Avatar
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    Check pins D14 and D16 on the 7747. After initial fire, the 7747 takes over firing the injectors. If D14 and D16 are not changing state, then you need a new 7747. If they do change state, you need to check wiring from 7747 to injectors.
    Square body stepsides forever!!!

  15. #15
    EFI GearHead ! EagleMark's Avatar
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    You've got some strange issues going on? What is this vehicle, transplant, hybrid, swap ? Need to double check wiring, there are power wires that are on all the time and others for Key On only, the Key On only need power from key on to crank and back to key on uninterupted.

    If something is really wrong with wiring it could be a fried ECM now?

    What Jim said about injectors, plus they get there power from positive source and the ECM is a ground for pulsing them.

    Take a look at diagrams:
    http://www.gearhead-efi.com/Fuel-Inj...Information-42

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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