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'99 Yamaha 150 HP OX66 erratic tachometer

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  • '99 Yamaha 150 HP OX66 erratic tachometer

    Left the dock at 10AM. Air temp was about 30 Deg F. During initial run out engine ran normal but Tachometer display was jumping from 35 to 45+/-. The display would show 35, then instantly jump to 40, 45, then back to 35. Engine did not act or sound as any speed changes were actually occuring. Actual engine speed was approx 35(00) which was the bottom range of the erratic display. After running for about 20 minutes tach stopped erratic display and acted normal for the next 4 hours of running.

    I'm getting ready to bring it to the boat doctor for its annual winter check up. I was just wondering what to expect to hear the issue may be.

    Other than replacing the "cam, trim sender" this engine has been bullet proof for almost 10 year now.

  • #2
    Re: '99 Yamaha 150 HP OX66 erratic tachometer

    Check the wires on the back of the tach, especially the ground. Sounds like you have a loose connection or some corrosion that is causing an erratic short. Just clean things up and give it a try.

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    • #3
      Re: '99 Yamaha 150 HP OX66 erratic tachometer

      Yep, that's exactly what I would say to check. These tachs are very sensitive to loose or corroded wires/connections, so take each one off and clean it. Also check your fuse for the tach circuit because they get dirty/corroded and need cleaning from time to time. My tach started jumping around when I hit a wake this summer and the problem was the in-line fuse, just needed cleaning(just a bit of corrosion). My boat/motor is a 1999 also and I have replaced the tach once, with one that is supposed to be "waterproof". I know my old tach would fog up with moisture on the inside sometimes during damp weather and that can't be good for the internals. Good Luck!

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      • #4
        Re: '99 Yamaha 150 HP OX66 erratic tachometer

        just flip the switches on the back and flip them back

        most saltwater boats happens every year from salt air
        HUMAN BUILT = HUMAN FIXED
        CERTIFIED MARINE TECH

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        • #5
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          Re: '99 Yamaha 150 HP OX66 erratic tachometer

          Thanks for the replies. As soon as it warms up above 30 degrees I'll go out and do a once over on the connections.

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