GT-40 limp mode/low RPM

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  • richard
    Senior Member of PLANETNAUTIQUE
    • Feb 2005
    • 406

    • HK


    #1

    GT-40 limp mode/low RPM

    I'm grateful if any body here can give advise to solve my GT-40 problem,
    my boat had 2001 SAN w/GT-40 engine,before have higher temp. symptom, until I solve this problem,used for about one year at 180F,when RPM runing over 2600,the temp guage seems tend over 180F,so I need to lower the RPM to let temp lower,finally,I solve it by change a 147F thermosat,now temp reading 160-170F, now another problem happen,first time was happen before changing the thermostat, the RPM,limited under 2500, when next time use ,it became ok at morning,when later use the same day,it happen again, and can't recover ,now the max RPM only2100-2600,even full throttle, when running, I can feel the engine vibration little stronger,max speed only 18KMH , I check the coolant, I notice the level become higher but later become lower when stoped so I add about 500ml water, I notice the coolant will become less running sometime,I check all sparkplug,all is fine but in dark color,(high temp recult? ) I hope some body will give me advise.
  • Coyote
    • May 2004
    • 9



    #2
    If the red "check engine light" on the dash is also on while the engine is running, then your boat is probably running in limp mode.

    If the oil and water temp gauges are reading normally (40lbs and 160 deg.) then the fault is likely to be one of two sensors on the engine.

    1. Oil pressure switch - located next to oil filter on extension pipe
    off the engine block. It is the smaller of the two sensors, the other
    being the oil sending unit of the gauge. The oil pressure switch is
    connect by a green wire to the water temp switch.

    2. Water temp switch - located at the front of the intake manifold
    (starboard side) and is connected to the engine harness by a tan with
    black stripe wire and the the oil pressure switch with a green wire.

    To test remove the green wire from the oil pressure switch and run
    engine, If the dash light goes off, replace the oil pressure switch. If
    it is still lit disconnect the tan wire with the black stripe from the
    water temp switch. If the dash light goes off, replace the water temp
    switch. If the light is still on then it is possible to have a short to
    ground or an incorrect connection at the black wire from the warning
    indicator light at the dash. If any electrical work (stereo
    installation, perfect pass, etc.) please check that this wire was not
    used for a ground.

    Comment

    • richard
      Senior Member of PLANETNAUTIQUE
      • Feb 2005
      • 406

      • HK


      #3
      Coyote:
      There are no red alarm lights,every thing looks normal,(volt meter,oil pressure,temp.) but low RMP,and can't speed up.

      Comment

      • richard
        Senior Member of PLANETNAUTIQUE
        • Feb 2005
        • 406

        • HK


        #4
        low RPM

        The problem solved by change the FCC filter,boat run nice again! :grin:

        Comment

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