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  1. #1
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    Default fuel pump and oil pressure cut off

    Bear with me. It is a 1978 boat , but has been repowered with a 5.7 Mercruiser motor. I think about a 2002 vintage. I don't have the serial number here with me. My brother just bought it. It was only supposed to need a fuel pump (electric). (where have we heard that before?) I checked the fuel pump bypassing the oil pressure cut off and it would try and start (the pump not the motor), but not run. Replaced the fuel pump still with the bypass hooked up ran the pump until it had gas coming out of the line going to the carb. Hooked the carb line up, choked it and it started and ran good. Idles good ect. Haven't had it out on the water yet, but that is another story. The issue is I hooked the oil pressure cut off switch back up and now the pump won't run. It is possible because of a low battery I am not generating enough pressure for the pump to run. The motor has good oil pressure.
    Last edited by freddyray21; July 28th, 2007 at 06:54 AM. Reason: clarify what won't run

  2. #2
    Moderator Bondo's Avatar
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    Default Re: fuel pump and oil pressure cut off

    The issue is I hooked the oil pressure cut off switch back up and now the pump won't run.
    Does the Switch Close when there's Oil Pressure,..??..??.....
    Test it with a Test Light or Multimeter........
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
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    Default Re: fuel pump and oil pressure cut off

    will do as it could be the switch. This motor is new and only supposed to have 38 hrs on it. Everything looks new, but I've seen new parts go bad before. I think also this sat for a few years after the motor was installed. We are taking it out on the lake today. I am taking my boat and a tow rope also. Shows what faith I have in my brother's purchase. I think after he gets all the bugs worked out it will be a good boat, but getting all the bugs worked out may drive me to the madhouse. He is very mechanically inclined, but big brother (me) seems to want to take over.

  4. #4
    Moderator Bondo's Avatar
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    Default Re: fuel pump and oil pressure cut off

    Ayuh,.......Good Luck......
    Any Grease is Better,..... Than No Grease at All.......

  5. #5
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: fuel pump and oil pressure cut off

    Here is the wiring diagram for the fuel pump if it will help. That switch should close at 6 psi.

    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  6. #6
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    Default Re: fuel pump and oil pressure cut off

    thanks Don that will help alot. I might need to check the electric choke also.

  7. #7
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    Default Re: fuel pump and oil pressure cut off

    it's got to be a bad oil pressure switch. Charged the battery fully so the engine spins very good and it won't run unless I by pass the oil pressure cutoff switch. Engine runs fine after doing that.

  8. #8
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: fuel pump and oil pressure cut off

    It's not the oil pressure switch if the pump doesn't run while the engine is cranking, that means you aren't getting power from the starter solenoid to the fuel pump wiring, nothing to do with the oil pressure switch.

    While the engine is cranking, you should have power to terminal D (see pic below) that puts power directly to the fuel pump. Use your meter and check for voltage at the solenoid and at the terminal on the switch.

    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  9. #9
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    Default Re: fuel pump and oil pressure cut off

    will do thanks again Don

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