Hesitation/inconsistent rpms and up and down idle.

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  • skiflyer45
    • Jul 2014
    • 16

    • Orlando

    • 1997 Ski Nautique 310hp
    #1

    Hesitation/inconsistent rpms and up and down idle.

    New owner of 97 Sn have been having this problem for a few days. It seems to be getting worse. It started with a slight hesitation that is now much worse as seen in this video. I have been using 87 gas...could that cause it?
    http://youtu.be/z9eSgtXrSi4

    I would appreciate any help.
    Tags: None
  • vortech347
    • Mar 2004
    • 95

    • Central Texas

    • 99 Sport Nautique - GT40 - FCT2 tower
    #2
    Is it a GT40? At least in my 99 it requires 89 minimum. We experienced issues with 87 octane gas when we first bought the boat where it would run fine pulling up a rider and then just drop 200 rpms. It turned out it was the knock sensor detecting knock and retarding the timing. As soon as I switched to 89 the problem went away.

    Check the owner's manuals available on this site to confirm.

    Also, if it's a GT 40 it has several sensors that can cause "hunting" issues. It's possible that's a cause but try the 89 octane first.

    Comment

    • skiflyer45
      • Jul 2014
      • 16

      • Orlando

      • 1997 Ski Nautique 310hp
      #3
      yea they recommend 89....I assumed 87...I will try and see what happens with 89. Thanks

      Comment

      • vortech347
        • Mar 2004
        • 95

        • Central Texas

        • 99 Sport Nautique - GT40 - FCT2 tower
        #4
        If that doesn't do it there are several sensors and the ecu that could be the problem. The GT 40 used a very similar fuel injection system to the Mustangs of those years (eec-IV).

        You could throw quite a few expensive parts at it that might be better served by having a trained technician find the problem.

        I had a real bad "hunting" issue with my boat from day one and we bought it new in 99. The dealer worked on it 2 or 3 times while under warranty and never really fixed it.

        At about year 10 I was so fed up I complained to PCM about it and they contacted my dealer. My dealer took a look again and in the end found out the ecu was bad. After doing several tests including a lake test where I met the technician at the lake, it was discovered the ecu was bad. The boat would run fine for a while and then just start hunting. The tech would tap the side of the ecu and it would clear itself up. His opinion was the ecu had a cracked circuit board.

        PCM and the dealer wound up selling me a new pcm for half price and only charging me 2 hours labor. So a bill that would have been $1000 plus wound up being $500.

        The ECU is a $500+ part and the other sensors can get expensive too.

        Hope it's just the fuel.

        Comment

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