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Marine Power 5.7 misfires after 1 hour

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  • Marine Power 5.7 misfires after 1 hour

    Hi all, new guy here, thanks in advance for any ideas. I recently bought a Alura 35 with twin Marine Power 5.7 straight inboards. Issue: port engine misfires after an hour of run time. I did full tune up (no other issues just for baseline) including plugs, coil, caps, wires, rotors, oil change and raw water impellers (FWC engines) they both start easily, idle well and run smoothly but after 1 hour port engine misfires/backfires etc. a bit less after tune up but still an issue. Temp is 160 oil pressure 60, I’m out of ideas for temperature related stuff thanks!

  • #2
    Its never the coil

    Are the motors carb or EFI?
    which ignition system?

    Backfire is usually running lean. So look at the fuel system

    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

    Comment


    • #3
      Thanks for the fast response!
      Carb engines, Mallory ignition (no points)
      Boat doesn’t have fuel crossover valves but I can probably try to switch the rubber hoses. Any idea what the fuel issue can be? Filter new and looks good, I dumped fuel out into glass to examine, nice and clear no water
      thanks

      Comment


      • #4
        Go thru the carb.
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

        Comment


        • #5
          BTW....welcome aboard
          Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

          1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

          Past Boats
          1970 Wooster Hellion - Merc 9.8
          2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
          1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

          What’s behind you doesn’t matter.Enzo Ferrari

          Comment


          • #6
            One other thing to check is the voltage at the +side of the coil, try to hook a volt meter to it when you first start the engine and leave it on, then see if the voltage drops when the backfiring begins. Your engine’s wiring harness may have had breaker points originally and the resistor wire could be the problem.
            Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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            • #7
              Malory dizzy needs a ballast resistor or you fry the module..... (ask me how I know this )
              Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

              Comment


              • #8
                I agree that they require a resistor the main thing is that the resistor is not “breaking down” after the hour or so of use. Experience has taught me that you cannot assume anything, these may be Petronics conversions. These engines may have been Marine Power replacement power heads without the electrical systems.
                This is a shot in the dark but have you ever tried replacing the rotor, sometimes they can also cause these problems when they heat up.
                Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

                Comment


                • #9
                  Thanks guys, as soon as the weather improves I’m on it

                  Comment


                  • #10
                    Originally posted by kenny nunez View Post
                    One other thing to check is the voltage at the +side of the coil, try to hook a volt meter to it when you first start the engine and leave it on, then see if the voltage drops when the backfiring begins. Your engine’s wiring harness may have had breaker points originally and the resistor wire could be the problem.
                    This. A coil replacement modue must "see" 12 volts. However, the coil must be ballasted (resistor), either internally or externally. A very common problem. A non-resisted coil draws too much current and overheats. Bottom line, the coil and the breaker module must be matched.

                    Most backfiring is electrical, or in rare occurrences mechanical. In my 50+ years experience, lean backfire seldom happens without other symptoms being present.

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                    • #11
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                      Does it just missfire at low rpm or all way through revs ? Just one engine ?

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