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Bad Fuel Pump Causing Gas In Oil?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Stoopalini, May 22, 2002.

  1. Stoopalini

    Stoopalini 1/2 ton status

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    Is it possible for a bad fuel pump to allow fuel into the oil?

    I changed my oil recently, and noticed there was a good amount of fuel mixed in with it. Someone suggested that maybe the diaphragm in the fuel pump is torn, and allowing fuel to get into the oil.

    I'm going to replace the pump regardless, because I noticed some fuel seeping out around the pump; but I would like to know if this has anything to do with the fuel-in-oil problem.

    Thanks,

    Thomas.
     
  2. Depdog

    Depdog 1/2 ton status Author

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    It could, it could also be a cracked head, I got my fingers crossed for you that its the fuel pump.

    Depdog
     
  3. Ryan

    Ryan Registered Member

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    Yep, it's possible - probably most likely the reason. The diaphrams were notorious for rupturing and letting gas into the crankcase. I put four pumps on in three years on a 305. Look at it this way - at least it's breaking up all that sludge in the bottom of the block. Maybe that's what kept mine running for over 300,000 miles!
     
  4. arq

    arq 1/2 ton status

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    it's usually the fuel pump diaphram, if it's a mechanical one. seems like your preEFI so i would check that before you tear down your engine.

    ARQ.
     
  5. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Those are possible solutions, and I have heard that a hung or misadjusted float can cause the carb to "seep" when not running (sitting in driveway), the gas goes into the intake, down the runner(s), into the combustion chamber, seeps past the rings, and into the crank-case. If the fuel pump is old, it is probably not a bad idea to replace it. If you do and it still leaks then I would check the carb. A buddy had the same thing with a bad injector on his TPI. The injector got some $hit in it, and wouldn't close from time to time. The pressure would bleed off through the injector and the fuel would go down the runner, into the chamber, past the rings, and into the crankcase, that is what made me think of the carb float. Whatever it is, I hope you fix it, thin oil is not a good thing especially on long runs.
     
  6. Stoopalini

    Stoopalini 1/2 ton status

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    Great, thanks guys. I'm hoping it's the fuel pump, although I have considered the fuel pressure pushing gas into the carb when it's sitting. I even replaced the gas cap with a vented one to try and keep the fuel pressure down when it's not running. I don't get the traditional 'Whoooosshhhh' anymore when I take the gas cap off after installing the vented cap.

    The fuel pump looks pretty old, and is even wet with gas; so for $10.99 (autozone special) I am going to replace it and see.

    As far as cleaning out the engine, I actually topped off my tank on Sat with diesel by accident /forums/images/icons/shocked.gif! Luckily for me, it only took 10 gallons, but with the gas-in-oil problem I have going on, I'm pretty sure any gunk that was in my crank case, bearings, etc is completely cleaned out LOL!

    Thanks again,

    Thomas.
     
  7. HarryH3

    HarryH3 1 ton status Author

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    If you look at the bottom of the fuel pump, there's a weep hole. It's there so that it's obvious when the diaphragm starts to leak. That should be why the pump is also wet with fuel. /forums/images/icons/cool.gif
     
  8. Stoopalini

    Stoopalini 1/2 ton status

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    Ya know, I thought there might have been a weep hole in that thing. Someone else even mentioned it to me.
    Thanks for the info Harry, that would definitely explain why it's wet around the pump, and not appear to be coming from the lines.

    This is great, definitely leads me to believe my gas-in-oil problem is the fuel pump, and not some other interal engine problem.

    Thanks guys /forums/images/icons/laugh.gif

    Thomas.
     
  9. Stoopalini

    Stoopalini 1/2 ton status

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    Well, I swapped out the fuel pump last night, and sure enough, that weep hole looked pretty bad. It was definitely leaking.

    The truck runs much better now /forums/images/icons/smile.gif Throttle response is back, and now my oil will stay ....... well ...... oil /forums/images/icons/wink.gif

    Thanks for the help guys,
    Thomas.
     

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