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I'm working on a boat (malibu responise LX) with a small block chevy engine, EFI, and an inline fuel pump.

After much diagnosis, I replaced the (inline) fuel pump on the premise that a seal had failed and air was getting in. It was losing prime after running for a few minutes.

A new pump, new fittings, reprimed, etc. The new pump pushes gas out into a jar all day long, and also circulates it through the over-pressure bypass all day long. Great, launch the boat, start it, and the pump loses prime.

Prime it again on the spot, it pushes gas again. Start the engine, loses prime.

Is there any difference in fuel supply by powering it blindly with 12v vs while the engine is running? I can't hear the pump running while the engine is running, but that's just because of noise.

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  • I'd think you should be able to feel the pump running during engine operation. Does it run with ignition on/engine off? Also, could you describe better by what you mean "it loses prime"? You are saying it just quits pumping fuel, correct? Have you put a fuel pressure gauge on the engine so you can see what it's doing at all times? Does the engine run at all when you go to start it? Commented Aug 31, 2022 at 18:04
  • Where is the pickup in the fuel tank and is there any baffling, etc? What I'm getting at is potential cavitation that might be happening because of movement. I have had similar issues in a car where the pump would only cavitate in long sweeping right turns. Turned out to be a partially-rotted pickup hose that was admitting air when the fuel sloshed.
    – Chris O
    Commented Aug 31, 2022 at 18:13
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    It seems to have just been air in the lines that has since been sorted - I was continuing to chase this problem when in fact the issue was not having spark. The pump sounded different immediately after the engine died, but I don't believe it's related as that was just a result of the battery voltage being different. Commented Sep 1, 2022 at 12:27

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