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Thread: Weird!

  1. #1

    Default Weird!

    New engine in the boat, (454 mercruiser in a ‘87 cobalt). Having a slight issue. Once the engine warms up I get what im assuming is a misfire (engine studders) between 1500-2000 RPM while at the same time the needle on the voltage gauge bounces around like crazy. Any ideas? Where would you start.

    also I’m getting engine feed back through my speakers.

    obviously an electrical issue, all my grounds look good, batteries are all good. I sanded all my ground contacts nice and clean with no change.

    thanks in advance!

  2. #2
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    5,263

    Default Re: Weird!

    Rotor windings in alt may be going bad

  3. #3

    Default Re: Weird!

    Quote Originally Posted by Bt Doctur View Post
    Rotor windings in alt may be going bad
    interesting point.. that alternator is maybe a year old and is making 14+ bolts while engine is running.

    is whatís weird is that the probably only occurs once the engine is warmed up and only between 1500-2000rpm. If I power through it and ask for my throttle the boat runs just fine.

    weird

  4. #4

    Default Re: Weird!

    Quote Originally Posted by Bt Doctur View Post
    Rotor windings in alt may be going bad

    could it be a bad ignition coil on it way out? I only ask this because the problem seems to happen only when the engine is warmed up all the way

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,927

    Default Re: Weird!

    It could also be a bad engine ground(s). I'd start the analysis by disconnecting the alternator (since that's easy to do).

    If no change, start looking for a bad ground(s)--which is much harder to do. It's entirely possible that, at that specific rpm, the vibration wiggles a bad connection enough to cause the problem, whereas the connection behaves itself other wise.

    Good luck!

    Jeff

  6. #6
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    6,000

    Default Re: Weird!

    Maybe the crappy BR6FS/MR43T spark plugs need to be changed..... They have a short life.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  7. #7

    Default Re: Weird!

    Quote Originally Posted by fastjeff View Post
    It could also be a bad engine ground(s). I'd start the analysis by disconnecting the alternator (since that's easy to do).

    If no change, start looking for a bad ground(s)--which is much harder to do. It's entirely possible that, at that specific rpm, the vibration wiggles a bad connection enough to cause the problem, whereas the connection behaves itself other wise.

    Good luck!

    Jeff
    yea I initially assumed it was a bad ground as well, especially because of the engine feed back coming through the speakers. But donít you find it odd that it wonít do it cold?

    boat runs fine for 40 mins or so then starts missing. And itís directly related to the voltage gauge because that needle bounces like crazy while the miss is happening.

  8. #8

    Default Re: Weird!

    Also, I just went out to the boat and disconnected the orange wire coming off the alternator. The speaker feedback I was getting is gone now.

    what in the heck is going on?

    i checked all my grounds, cleaned all the contacts, everything is tight.. I don’t understand!

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