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fuel pump making a knock?

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  • fuel pump making a knock?

    Can a bad fuel pump make a knocking sound similar to a bad bearing? My 3.8 began losing power just after getting on plane a few days ago, then shortly thereafter developed a knock, sounding like a bad bearing. The timing is good, I've checked it running on fresh gas, it's not getting hot, and it has 50 lbs. of oil pressure at idle. All ignition parts are new, or very recent. Engine starts right up and idles very smoothly, but it has a very rythmic knock at idle that increases with speed. The outdrive is off the boat and the engine is ready to be lifted out, but before I take any covers off I'm going to remove the fuel pump and inspect it. Any comments?


  • #2
    Re: fuel pump making a knock?

    I'v heard mechanical fuel pumps knock on more the a few occassions. You can listen to it with a long screwdriver placed on the pump and to your ear just for proof.
    Of those who receive good advice, only the wise will profit from it.

    If you need it....Get it
    If you want it....Wait
    If you have it....Flaunt it


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    • #3
      Re: fuel pump making a knock?

      If the fuel pump is making this knock, will there be something obviously wrong that I can feel or see when I take it off? Such as a loose arm?

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      • #4
        Re: fuel pump making a knock?

        Usually thats the case. You can also operate the pump by hand (once removed) and typically hear the knock if it not an obvious problem.
        Of those who receive good advice, only the wise will profit from it.

        If you need it....Get it
        If you want it....Wait
        If you have it....Flaunt it


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        • #5
          Re: fuel pump making a knock?

          Thanks. I expect to take a closer look within the next couple of days. I haven't taken the motor out just yet, but it's completely disconnected. I may hook up the wiring and a garden hose and start it again to have a closer listen to the pump before I do anything else. The engine has about 100 hrs on it since a total rebuild and this is the first noise like this that I've heard. At this point I hope it is the pump, rather than a bearing. After all, there are a lot of fish that need to be caught out there!On a more personal note, I recently finished 6 months of chemo for a bad case of cancer, and I've only been fishing once this year, so I want to get it going real soon. Thanks for the help,Jack

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          • #6
            Re: fuel pump making a knock?

            Glad to help Jack. Good luck with the chemo treatments, but more luck with the boat. They usually require more attention than we do.
            Of those who receive good advice, only the wise will profit from it.

            If you need it....Get it
            If you want it....Wait
            If you have it....Flaunt it


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            • #7
              Re: fuel pump making a knock?

              i hear that RP!! seems like mechanics should get paid like doctors and doctors paid like us!! doctors just git-r-close and the body heals itself!! no getting it close on an engine, cause it aint gonna fix itself...
              My wife say's I spend too much time with my boats. I said "ok, I'll start spending time at the bar!" She said, "I really like the boats...."

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              • #8
                Re: fuel pump making a knock?

                I hope you have heard the Mechanic/Doctor joke. A Mechanic asks a Doctor at a party why he gets so much more money doing the same thing he does, you know, change valves, thats type of thing. Doc says try doing it with the engine still running....

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                • #9
                  Re: fuel pump making a knock?

                  Reel Poor; I have the pump out. There's a little play in the operation of the pump lever. When I hold the pum in one hand and tap it with my other palm it makes the same noise I've been hearing with the engine running. Is there supposed to be any play at all in that lever when the pump is out?

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                  • #10
                    Re: fuel pump making a knock?

                    The return spring has either weakened or collapsed. There should be no play in the lever. The rap you hear is the lever rebounding each time the cam comes around to push the lever. Ask me about the brand new small block Chevy that was rebuilt because of a bearing rap only to find the problem wasn't fixed. The cause - weak fuel pump return spring!

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                    • #11
                      Re: fuel pump making a knock?

                      I have never been so happy to have a bad fuel pump. Thanks so much for all the help!

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                      • #12
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                        Re: fuel pump making a knock?

                        Good News!!!!
                        Of those who receive good advice, only the wise will profit from it.

                        If you need it....Get it
                        If you want it....Wait
                        If you have it....Flaunt it


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                        Comment


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