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Thread: Engine Help.

  1. #1
    Member hoose35's Avatar
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    Default Engine Help.

    I have a pretty new 5.7 EFI enginge in my boat, 2 years old, 150 hrs. It has always ran good for me since I installed it. I took the boat out about a week ago, and while I was idling in to the harbor, I noticed a sound I had never heard before, it was like a hissing sound and it got louder and louder, then it went away and the engine started to sputter for about 10 seconds, then it smoothed back out. When I got home, I changed spark plugs, and ran some fuel injector clean in the gas. I took the boat out again today. While leaving the harbor everything was normal. After about a 15 mile ride, I started doing some trolling at idle speed. After awhile, the noise that I heard the previous outing returned, and the same sequence happened, the noise got louder, then went away, the engine sputtered for 10 seconds, then smoothed out. This process repeated itself about every 3-5 minutes. The noise sounds like it is either coming from the fuel pump, or the heat exchanger/thermostat area. I had done a couple things to my boat since the last time it ran good. I changed the fuel filters out, and I plumbed in my cabin heater which comes from the fresh water cooling system. I am really confused about what is going on here. It idles fine when the engine is cold, and it runs good when I am at cruising speed. It seems to run crappy after the engine has warmed up and I am idling. At no time did my engine temp change after it got to it's normal operating temp, 140 degrees. Does anyone have any idea on what could be going on?

  2. #2
    Member SuYentna Dave's Avatar
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    I would look for a Vacuum leak coming off the engine intake manifold. If it was a ignition issue it could be corrosion on the sending unit by the flywheel or a loose wire. If it is a fuel pump they tend to have issues at cruising speed not at low rpm's. Definitely a gremlin, I had a hose on an EGR valve fall off where it feeds into the intake manifold and it produce a hissing sound that was actually a sucking sound.

    Good Luck

  3. #3
    Member hoose35's Avatar
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    I did some troubleshooting today. I ran the engine for about 30-40 minutes before it started to make the hissing noise. I have a bleed port on the fuel line after it the fuel collector and return line. When the enginge started to run rough, I pressed the bleed port and I was getting some air. Also I looked at my fuel flow and it said 0 gph in between these cycles I am getting. It seems to my that the pump is pumping all the fuel out of the filter bowl and then sucking some air, then it seems like it fills back up with fuel, when it smooths out my fuel flow jumps up from 10-20gph and then after a minute it falls back to zero, I think I will bypass that fuel flow sensor and see if it changes anything, maybe it is clogged up? Any ideas?

  4. #4
    Member SuYentna Dave's Avatar
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    I have a In-Line gas Filter right before the fuel pump that has a clear tube. I Bought it years ago at NAPA when I got some silcon worms in my fuel tank. The one nice thing is I can visually check the flow going to the pump.
    If the Hiss you hear is a small slight hiss? Try a little talcum powder puffs in the air to see if you can see any unusual air movements. Do you have a electric fuel pump feeding the fuel rack or is it an manual pump? Is your fuel line in good shape, not dry?

    Good Luck

  5. #5

    Question

    Overflow of some liquid on a hot engine causing a steam/hissing noise??? Stuck thermostate, causing coolent to leak out and cause the hissing??? Hole in an exhaust hose causing water to hiss on a hot engine, only does it on step when the boat is tilted??? Bilge issues??? Mermaid's partying??? Gremlins??? I don't have a clue without being on it, just throwing out stuff to ponder, sorry I got nothing. Good luck.

  6. #6
    Member SusitnaAk's Avatar
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    Mine had a crack in the fuel line, I would check them, I couldn,t see it, but i could hear it sucking air. i shut the motor down removed line from the filter and blew into it that,s how i finally found it.

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