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  1. #1
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    115 Optimax Fuel Starvation

    S/N 1B757070

    Fuel/Air pressure at idle 108/95

    Pulse pump is drawing fuel fine from tank

    Fuel filter is new and clean

    Fuel lines new from tank to pulse pump as per recommendation of this site

    Boat gets on plane fine then appears to run out of fuel after a few minutes, bulb stays firm and pumping it has no effect on engine when it dies

    Compression good on all three cylinders and plugs look fine

    VST cleaned and pulse pump rebuilt, engine sit for at least a few years

    Fuel tank was drained and refilled.

    I have read about the high pressure pump bushing in VST causing issues, would my pressure still be good at idle if bushing is bad?

    Any other ideas

    Thanks

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    #2
    not likely usualy when it splits no start ,hook up a known good alternate tank and line assembly to mtr eliminate boat tank and line as source of problem
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #3
    Thanks Joe …… I will try that soon

  4. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #4
    Quote Originally Posted by wed68
    VST cleaned and pulse pump rebuilt, engine sit for at least a few years
    Can you confirm the order in which this statement occurred (is it exactly as stated)?

    VERY important question!


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #5
    Sorry my order was wrong

    engine sat unused for years, rebuilt pulse pump, cleaned VST and replaced lines before trying to start

    I also did the oil pump prime sequence before initial start up

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #6
    Need to get a set of dual-pressure, glycerin-dampened gauges on the engine, and monitor BOTH the low pressure fuel and high pressure fuel readings WHEN ENGINE dies off. Have someone take a cell phone and record it on video so you can safely operate the boat (keep the hammer down for a while so that the recording shows the pressures when the engine begins to drop off, all the way to it dying).

    This will help draw a much clearer picture of what is occurring (and of course, check primer bulb to make sure it's pumped up BEFORE and AFTER this video).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #7
    Will do Don thank you

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    #8
    Ran on remote fuel tank with same symptoms

    When engine dies fuel pressure drops sharply to 15 psi and holds steady, air pressure drops slowly to 70 psi then very slowly continues to fall

    When engine rpm is increased under load neither air pressure or fuel pressure drop, they are steady at fuel 108 and air 95

    thanks for yalls help

  9. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #9
    Need to be able to see LOW PRESSURE and HIGH PRESSURE fuel pressures (at same time). This is important... as it helps to know whether the engine is running out of fuel, the pressure just suddenly dumps out of no-where, etc.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #10
    The fuel low pressure side is the valve on the VST?

  11. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #11
    Correct. Need to be able to see the pressure from that fitting, AND the pressure from the Fuel Pressure Fitting on the fuel rail, simultaneously, before and during the problem.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #12
    Low pressure drops from 26 to 18 quickly then very slowly lowers
    high pressure side drops from 108 to 15 quickly then holds steady

  13. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #13
    Quote Originally Posted by wed68 View Post
    Low pressure drops from 26 to 18 quickly then very slowly lowers
    high pressure side drops from 108 to 15 quickly then holds steady
    The key was still on for all of these numbers (ie: Engine just spontaneously stalled on it's own)?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #14
    Correct

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    #15
    It’s very random ……. Could it all be electrical?

  16. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #16
    Possibly... but knowing which one dropped FIRST is the key.

    If the low side dropped first, and shortly thereafter the high pressure plummeted and the engine died: That's a fuel STARVATION problem.

    Can be caused by anything between the level in the fuel tank, and the low pressure fuel pump (including the float/needle in the VST).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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    #17
    I can not work on it for a week due to work starting tomorrow ……… stand by I will update soon
    Last edited by wed68; 07-15-2021 at 07:04 PM.

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    #18
    Quote Originally Posted by wed68 View Post
    It’s very random ……. Could it all be electrical?
    not likely
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #19
    Got a small reprieve from work and jumped on boat troubleshooting, remember boat set up for year! Found rat damage under console! Splice a few wires back together and dropped it in water. Ran flawless! Thank you Don your diagnosis that it looked like key was killing engine is what clued me into looking at wiring. Thanks all for the replies!

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    #20
    .................................................. ...the scariest thing in life is the unknown ...................................