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355 VS Clubby - fuel pump issue - HELP

Discussion in 'VR - VS Holden Commodore (1993 - 1997)' started by ScottyDot, Feb 6, 2018.

  1. ScottyDot

    ScottyDot New Member

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    Hi,
    My Clubby stopped in the driveway the other day.... realised the fuel pump wasn't running. It's an in tank Walbro 255ltr/min. Ended up changing the oil pressure switch. Now after 2-3 seconds of the key being turned to the on position the fuel pump runs constantly and she winds and won't fire. It's not until a pull the EFI relay that the pump will stop. Fuses all okay. Fuel pump relay getting power. If I bridge the fuel pump relay though it doesn't make the pump work??
    Put the old oil pressure switch in - back to no fuel pump at all.
    I assume I have a wiring problem on the OEM side - hoping not the ECM.
    Has anyone had this problem before? What did you find?
     
  2. BlackVXGTS

    BlackVXGTS Well-Known Member

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  3. immortality

    immortality Moderator Staff Member

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    When you turn the Key to the on position the PCM is supposed to run the fuel pump a few seconds to ensure the fuel rail is pressurised correctly and the pump should then stop. Once you crank the engine and it starts the oil pressure switch provides power to the fuel pump circuit but the pump should stop when the engine isn't running as there is no oil pressure to activate the oil pressure switch. This is a safety feature. See wiring diagram below. If the pump runs when the engine is not running via the oil pressure switch than most likely that is faulty.
     

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  4. ScottyDot

    ScottyDot New Member

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  5. ScottyDot

    ScottyDot New Member

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    .
    I've tried x2 new pressure switches now - still does the same thing - if I put the old oil pressure switch in - I get no prime and no constant pumping.
    I'm really starting to think PCM or wiring?
     
  6. ScottyDot

    ScottyDot New Member

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    .
    That's an awesome diagram though, I'll definitely keep that to future my testing - Thanks
     
  7. ScottyDot

    ScottyDot New Member

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    With that diagram I have found the signal to the relay is coming out of the PCM, but isn't at the fuel pump relay. I'll start buy rewiring that and see what happens
     
  8. Deuce

    Deuce Super Stock

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    There must be a safety override on this. I removed my oil pressure switch and drove ~30km across town and back a few years ago and it went fine. It would have easily drained the fuel lines 20times over if the pump didn't keep them pressurised.
     
  9. ScottyDot

    ScottyDot New Member

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    So update, with the diagram - I worked out that most of my relays aren't in the marked locations - so I then found the pump relay was no good. Replace it and my prime cycle worked. Then found a bent pin at the old pressure sensor - straightened and refitted - no constant pumping -all sorted
     
  10. immortality

    immortality Moderator Staff Member

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    VR may be wired slightly different.
     
  11. Deuce

    Deuce Super Stock

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    True
    Thats good to hear that you fixed it
     
  12. EYY

    EYY Well-Known Member

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    The oil pressure switch provides power to the fuel pump on earlier models vs2 and prior - but only as a backup if the fuel pump relay fails. This means that it’ll still start if the relay isn’t triggered by the pcm, but it’ll take some time to crank it until oil pressure comes up to supply power to the fuel pump.

    Only reason I know about this is because mixer style lpg systems rely on the factory safety setup to close all solenoids in the event of an accident/engine stalling.
     

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