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Symptoms Of A Dying Fuel Pump?

Discussion in 'Flat Fender Tech' started by garage gnome, Apr 12, 2020.

  1. Apr 12, 2020
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    What are the signs that a mechanical fuel pump is dying? Twice I’ve been out with my Jeep, and it died. Acted like it’s vapor lock, but I’ve never had any issues with that before. It’s not that hot out either. Stock L134 with a carter fuel pump from rock auto. Pour some gas down the carb and it starts up then dies. Repeat this process and eventually it goes.

    I’ve blown the fuel lines out from the tank and have good fuel flow through them. I also took the fuel line off at the tank and gas just pours out, so I know that the line isn’t plugged in the tank. Looking for ideas. I have another new fuel pump I could put on. :shrug:
     
  2. Apr 12, 2020
    Lockman

    Lockman OK.....Now I Get It . 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Silver Hill,...
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    Then.....Put it on, Sir .Third strike yur out ! :schooled:
     
  3. Apr 12, 2020
    Sierra Bum

    Sierra Bum Member

    The High Sierra
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    I’ve had a few mechanical pumps go out over the years....mostly older American pickups. Seems like often times they will function ok with no load...flat roads or idling...then start dogging when demand increases, like going up a hill. Then soon, they stop working.
     
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  4. Apr 12, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
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    When the mechanical when out on my v6, it died over a bit of time and usage, progressively getting more and more noticeable. The symptoms mentioned were right on with mine...
    yup

    also yup...
    One additional thing for my pump at least is that it leaked fuel through the diaphram and into the oil - I started to notice the oil smelling very gas rich - but as the jeep was very new to me i wasn't exactly sure....regretted I didn't figure it out sooner as I think it did some engine damage contaminating the oil.
     
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  5. Apr 12, 2020
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    Yep, seems like it quits when I need the power.
     
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  6. Apr 12, 2020
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    My first thought too. I just changed the oil and it didn’t smell like gas. Maybe I’ll change it before it gets to that point.
     
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  7. Apr 13, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Have you tried Sea Foam? I've come to the conclusion that a check valve can stick and even if the diaphram is good it will lose suction.
     
  8. Apr 13, 2020
    duffer

    duffer Rodent Power

    Bozeman, MT
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    Just hook a pressure gauge up to the line to the carb and see what the pump is actually putting out.
     
  9. Apr 13, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Yep. A tiny speck of crud in a valve will kill the pump output.

    Ditto on the gas-in-oil syndrome.

    And the loss of power under load is typical, but ALSO can be a restricted filter.
     
  10. Apr 13, 2020
    Lockman

    Lockman OK.....Now I Get It . 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Silver Hill,...
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    You've got a new pump...... R & R Time ! :bananatool:
     
  11. Apr 14, 2020
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    Really simple possible fix; is the gas cap vented? A sealed cap can nearly pull a vacuum on the fuel tank. I had this issue decades ago, with the same symptoms you are having.
    -Donny
     
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  12. Apr 24, 2020
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    Just to update, I pulled the pump apart and found a piece of red plastic in one of the valves. :rolleyes: Put it back together with a filter before the pump and all is well.
     
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  13. Apr 24, 2020
    jeep2003

    jeep2003 Well-Known Member

    Upstate NY
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    The first time i had a problem the diaphram went bad gas leaked out the bottom drain hole. I bought a new pump only lasted about a year and the valves went bad. I just went to start it up one day and it only ran on the fuel in the carb then quit. I knew it wasnt getting gas. So I put the bottom half of the new pump on with the top of the old pump and its been good
     
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  14. Apr 24, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I've done the exact same thing. At least the diaphragm in the new junk ones is decent enough to use.
     
  15. Apr 27, 2020
    jzeber

    jzeber Well-Known Member 2022 Sponsor

    Morgan Hill, Ca
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    I had this happen to me last year. 2 or 3 year old fuel pump. It would start and run until I hit a small incline and then would die. I tracked down everything including dropping the tank. Finally put in a new fuel pump and it is running great.
     
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