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  1. #1

    Default HELP!!!!Changed fuel pump and ECM. fuel pump still wont turn on

    I am working on my uncles 99 chevy 5.3 and he was told the ecm was bad so I changed that out and still nothing from the fuel pump. I had a known good fuel pump that I dropped in and still nothing? What else do I need to look at? I am a cummins diesel guy so not sure where else I need to start looking on this truck. Thanks for the help.

  2. #2
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    stephan's Avatar
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    Welcome to the club Stang. About all that's left that you haven't done so far is the FP relay & the wiring loom. Look for the FP relay on the firewall a little left of center
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  3. #3

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    Quote Originally Posted by stephan View Post
    Welcome to the club Stang. About all that's left that you haven't done so far is the FP relay & the wiring loom. Look for the FP relay on the firewall a little left of center

    I swapped out the relay as well. Could it be the PCM/fuse panel itself? Which wire is the power wire at the tank that I need to check for?

  4. #4
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    Have you checked the relay to see if it's getting power to & out? I don't know the color for your truck cuz my diagram is not for that year, but it shows tan & white wire for the FP prime.
    Have a helper turn the key while you check for power into & out of the relay.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  5. #5

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    Have you done a fuel pressure test? The two heavier wires at the pump should have 12V for about two seconds when you key on.
    When you hear hoofbeats, look for horses not zebras.

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