WOT issue

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by sarbog, Feb 10, 2018.

  1. sarbog

    sarbog Member

    135
    Aug 22, 2008
    Emerald Isle NC
    '05 340 Sundancer
    Garmin 7610xsv
    1951 Penn Yan 9' Aerodinghy/2018 AB 9vl w/ 15 hp Evinrude 2-strk
    Twin 8.1 Horizons v-drives
    Help. ’05 340 w/ 8.1 Horizons. End of last season I noted the port engine lagged (needed more throttle to maintain same RPM as strbd). Major maintenance year as risers and manifolds were changed. Also had the injectors cleaned. Test run last week and strbd engine good but port still only gets to about 4200. Starts and runs smooth. Everything on the engine checks in spec, just won’t get full wot rpm. At lower rpms (cruise rpm) it lags slightly but then slowly comes up and matches the strbd. I can not afford to just start replacing things willy nilly. It seems like perhaps a fuel issue. Suggestions on where to start. Want to resolve this before the season gets here.
     
  2. Espos4

    Espos4 Active Member

    586
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    How about a fuel pressure gauge and an assistant to record the reading as you cruise around at different rpm’s, all the way up to full throttle.
     
  3. juggernaut1

    juggernaut1 Active Member

    828
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    Could be plug wires and or plugs. How old are these items and when were thhey last replaced? I had a wot issue develop on one of my 8.1s and it was a plug wire - no tell tail signs otherwise though except for not reaching wot.
     
    Last edited: Feb 10, 2018
  4. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    How were the injectors cleaned? Were plugs replaced at same time? How did the plugs look? Are the plug wires original from 2005? Age of fuel? Has it been treated? Water separators replaced?
     
  5. sarbog

    sarbog Member

    135
    Aug 22, 2008
    Emerald Isle NC
    '05 340 Sundancer
    Garmin 7610xsv
    1951 Penn Yan 9' Aerodinghy/2018 AB 9vl w/ 15 hp Evinrude 2-strk
    Twin 8.1 Horizons v-drives
    Full tuneup with new plugs, filters, etc. I honestly don’t know how old the plug wires are. Other than buying new ones and seeing if that fixes it, how can I check the wires?
     
  6. Espos4

    Espos4 Active Member

    586
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    An ohm meter is one method.

    Look for something Online for a reference on what the resistance should be.

    Another option, run the engine in the dark. Look for spark jumping through the outer wire jacket.

    You could even spray some water on the wires to help induce the spark if necessary, or if you’re really brave, feel the wires with wet hands while the engine is running!
     
  7. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    CF3 issues. Is this why you had your injectors cleaned ? Replace those wires if they're original
     
  8. sarbog

    sarbog Member

    135
    Aug 22, 2008
    Emerald Isle NC
    '05 340 Sundancer
    Garmin 7610xsv
    1951 Penn Yan 9' Aerodinghy/2018 AB 9vl w/ 15 hp Evinrude 2-strk
    Twin 8.1 Horizons v-drives
    the CF3 issue came to my mind and the Service Dept at the marina is going to investigate the CF3 possibility. They have my engine serial numbers and will contact Mercruiser to verify my engines are among those affected. I will probably go ahead and replace the wires as I am the second owner and can not verify if they were ever replaced.
     
  9. JVM225

    JVM225 Well-Known Member

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    Probably dumb questions but:
    Are the tachs both accurate? What does the synch gauge tell you?
    Either way, new filters, plugs and wires in a boat that’s new to you is always a good investment.
     
  10. sarbog

    sarbog Member

    135
    Aug 22, 2008
    Emerald Isle NC
    '05 340 Sundancer
    Garmin 7610xsv
    1951 Penn Yan 9' Aerodinghy/2018 AB 9vl w/ 15 hp Evinrude 2-strk
    Twin 8.1 Horizons v-drives
    SYNC gauge reflects the difference. I have had the boat 4 years and this is a recent development. In course of maintenance only the plug wires have never been changed.
    In terms of using the boat it really doesn’t affect much. At my normal planing rpm, 3500+/-, all is fine. But there is clearly an issue that needs addressed. Just have to get to the cause.
     

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