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sporadic alarm on Mercruiser

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    sporadic alarm on Mercruiser

    I have twin 5.7 mercruiser gas engines on my 3488 byliner. There boat is 2002 I think the engines are 2001. Occasionally with no apparent pattern the alarm on the strb engine goes off and then a few seconds later it goes silent. As far as I know only 3 things trigger that alarm. 1. Low oil pressure 2. high closed loop coolant temp 3. high tranny fluid temp. During this alarm the oil pressure gauge and water temp gauge stay unchanged and normal. I have changed out the tranny high temp switch, the oil pressure low switch and the water high temp switch. I also had the tranny fluid cooler rebuilt and pressure tested. .On a recent run no alarms during a 2 hour run. However on the 2 hour return trip the alarm sounded for a few seconds about 3 times during the first 20 minutes of the trip and was then quiet for the rest of the trip. I am running out of ideas on how to fix this seemingly random alarm. i am beginning to suspect a small break in the insulation on the alarm wiring which goes to ground and sets off the alarm due to vibration. I have also learned I think that the high water temp switch feeds into the thunderbolt V ignition system and retards the spark advance if this switch is activated. The engine runs fine during these alarms.

    Have any of you ever had a similar problem and what have you done about it? Thanks for any help

    #2
    The alarm circuit uses separate sensors than the helm gauges so it’s possible that one of the alarm sensors is going bad. You can try disconnecting then one at a time to see which one was causing the alarm to sound.
    1997 Maxum 2400 SCR 5.7LX Bravo II

    Mike

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      #3
      Thank you for your response. I agree that the oil pressure and water temp alarms are separate from the sensors that feed the oil pressure and water temp gauges. I try to call the alarm sensors switches since they are either on or off. That thinking led me to changing out the oil pressure low switch, the water temp high switch and the tranny fluid high temp switch. The sporadic alarm is still coming on which leads me to thinking there might be a crack in the insulating wire or a connection problem. I may run some new wire to each of the switches to see if that works.

      Any good ideas are appreciated. I hate sporadic alarms since they are hard to trace and fix.

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        #4
        I would next disconnect the tan wire from the alarm itself to isolate the engine wiring vs a bad alarm.
        1997 Maxum 2400 SCR 5.7LX Bravo II

        Mike

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          #5
          It’s possible the wire has been chafed and occasionally “grounds” out against something DC negative. Maybe start the engine and let it idle while you wiggle the wire harness around in an attempt to get it to trigger the alarm. Or run a new temporary trigger wire to test if your issue goes away.
          Dave
          Edmonds, WA
          "THE FIX" '93 2556
          Carbureted 383 Vortec-Bravo II
          The Rebuild Of My 2556 https://www.baylinerownersclub.org/f...76?view=thread
          My Misc. Projects
          https://www.baylinerownersclub.org/f...56-gctid789773

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