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Thread: Help! Truck dies after ~20 seconds

  1. #1
    Fuel Injected! Xenon's Avatar
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    Help! Truck dies after ~20 seconds

    Well, got the tbi set up on my truck and got her started... Starts great and has a good idle compared to the old carb but it dies after 20ish seconds, every time. I'm thinking maybe its not getting a signal from the oil pressure switch? Or???

    Thanks in advance for the help!

    Matt
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  2. #2
    RIP EagleMark's Avatar
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    If you have the fuel pump realy working then there is no need for Oil Pressure switch, it is redundant... run 12 volt power to the red wire hanging from fuel pump relay, this will power pump always and see if relay is failing?

    20 seconds is strange? Some vehicles had a fuel pump run for 20 seconds... little gray box?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #3
    Fuel Injected! Xenon's Avatar
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    First off the fuel pump relay is the things hanging on the top right of the firewall, right?

    The red wire hanging from it, with the little spade connector on it? Did that on an s10 blazer once so I think know what you're talking about.

    Will try that and report back :)

    Thanks!!!!
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  4. #4
    RIP EagleMark's Avatar
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    Right!

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

  5. #5
    Fuel Injected! Xenon's Avatar
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    Ok, just tried that and it still dies after about 20 seconds and he relay chatters...

    Any idea what is wrong?
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  6. #6
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    relay chattering would be the low-load portion of it(that switches the high load) not getting enough current to keep it on.... either a very resistive wire giving it +12V or ground or the relay itself is heating up and causing too much voltage drop internally....

    if you have a spare somewhere, i'd try it.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  7. #7
    Fuel Injected! Xenon's Avatar
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    Are the two relays the same? I have the pair from another truck but don't know what's what...
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  8. #8
    RIP EagleMark's Avatar
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    Pretty sure they are both identical, just pop them out and look. 4 or 5 terminal.

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

  9. #9
    Fuel Injected! Xenon's Avatar
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    Tried replacing the relay and still nothing ... If you turn he key on and don't start the engine, you can hear the pump run for 20 seconds and then turn off.

    Am I not using a heavy enough wire or good enough connections to jump the relay, causing the chattering?

    Or is there anything other than he relay I should be looking at?

    Thanks guys
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  10. #10
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    most automotive relays only use ~1/6 of an amp to turn/stay on.... you can probably safely run one on 20 or 22 guage wire and never have an issue. i don't think i would go thinner than 18 though.

    could bypass the relay by removing it and sticking an appropriately large wire in the load terminals to see if it will start running longer.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  11. #11
    RIP EagleMark's Avatar
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    You've got the gray box 20 second fuel prime on that vehicle. If it is not a relay issue something is wired wrong from the box. Some do not have this and only prime pump 2 seconds, not 20.

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

  12. #12
    Fuel Injected! Xenon's Avatar
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    Ok, this makes me think maybe I'm chasing the same problem as 2 years ago when I switched to carb.

    When it died on me, the ECM 1 fuse blew and I had no fuel... Replaced the fuse and still nothing. Not knowing much about tbi at the time I assumes the ECM died and I switched to carburetor. Since then I've learned what a stupid thing that was and am switching back to tbi...

    What could've went wrong to blow the ECM 1 fuse and keep he pump from running?

    Also, where is this grey box you speak of?

    Thanks!!!
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  13. #13
    Fuel Injected! Xenon's Avatar
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    Does anybody happen to have a wiring diagram for the grey box setup? From what I found on google the heavy duty trucks had it... Guess mine has it because its a 8600lb gvwr...
    -Frank

    1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
    1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears

  14. #14
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    here's both single and dual fuel tank diagrams.

    http://i.imgur.com/Dfkjv.png
    http://i.imgur.com/gmbXO.png
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  15. #15
    RIP EagleMark's Avatar
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    If you look closly at diagrams in the 1227747 info thread you will see one has the 20 second fuel primer... one does not...

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

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