Engine dropping RPMs while warm and dying at idle
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Engine dropping RPMs while warm and dying at idle

  1. #1
    Austin Boater
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    Default Engine dropping RPMs while warm and dying at idle

    I have a Mercury 6.2L that I am having some challenges with lately. I have replaced the ignition assembly, plugs, fuel filter wires and IAC on it. It runs really well when it is cold and even for a long while when warm. But after a good hour of running, it will start to drop RPMs. While cruising at 3500 RPM it will drop to 1500 or so every couple minutes. It is very regular on the timing when it drops RPM. It is not occasional when it drops, it is every couple minutes or so. Also when idling it will just flat out die every couple minutes.

    I have no idea. Took my mechanic out yesterday with the computer. No codes and everything looks good. He says it looks like someone turned the key off when it dies. We inverted the kill switch to rule that being faulty out. He doesn't have any great ideas about it. After he left yesterday he wanted me to clean all the battery terminals, that didn't help.

    Any good ideas here?
    2005 Sunsation Dominator 32 - twin 400 HP Full Throttle Marine 383s

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  3. #2
    New here Beer:30's Avatar
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    Old fuel? Water in fuel? Does it do it on both tanks if you HAVE two tanks? Sounds like bad fuel.
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  4. #3
    Austin Boater
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    New fuel yesterday, other engine is running great. Single tank.
    2005 Sunsation Dominator 32 - twin 400 HP Full Throttle Marine 383s

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    Highaboosta Unchained's Avatar
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    Checking the battery terminals was a good call.
    I had that problem.
    Check the negative cable to the block also.

    Check any and all grounds from the ECU to the battery.
    Any fuses that are not making a real good connection can be a problem area.
    Disconnect the weatherpack terminals and spray WD40 inside.

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  7. #5
    Austin Boater
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    I tried checking the ground for the negative to the block, tried tracing it back but lost it about middle of the way. Where is it located?
    2005 Sunsation Dominator 32 - twin 400 HP Full Throttle Marine 383s

  8. #6
    Senior Member GT Jets's Avatar
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    Quote Originally Posted by Captain YARRR View Post
    I tried checking the ground for the negative to the block, tried tracing it back but lost it about middle of the way. Where is it located?

    Should be either on a motor mount or at a bell housing bolt that is configured like a stud.

    What was the fuel pressure, have you ruled out a failing fuel pump?

    Being as it runs well while cold, I am going with a fuel issue of some sort.
    GT


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    Senior Member uniboarder's Avatar
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    I watched my friend go through this yesterday. It was a recurring problem I guess. Bypassed the whole throttle cable assembly and hooked up direct to throttle. Bam, on the water. Its the little limit switch that cant snap "UP". Or is it because it drops down? To many electronics for me to know....

  10. #8
    Senior Member GT Jets's Avatar
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    Quote Originally Posted by uniboarder View Post
    I watched my friend go through this yesterday. It was a recurring problem I guess. Bypassed the whole throttle cable assembly and hooked up direct to throttle. Bam, on the water. Its the little limit switch that cant snap "UP". Or is it because it drops down? To many electronics for me to know....

    Do you mean the shift interrupt?
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

  11. #9
    Austin Boater
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    Still having the same issue but noticed this weekend that as I hit waves the RPM would drop and rise with the waves about 500 RPM.

    Does this help point something out?

    I will check the throttle assembly. That could make sense, had those changed last year.
    2005 Sunsation Dominator 32 - twin 400 HP Full Throttle Marine 383s

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