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Need HELP!

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  • Need HELP!

    I bought a 1987 Chaparral 20' boat with the Mercruiser 230, V8, 5.0L Thunderbolt IV ignition system. I am at my wits end chasing a starting issue. Put on a new carburetor, ignition coil, cap, rotor, and spark plug wires. Sometimes it starts, sometimes it doesn't. Been checking the voltage at the + positive side of the coil and get around 8v with key on. (No start), Other times when I turn the key on, I get almost 12v (11.5v) and the boat will start. All the wires are connected and cleaned. What is causing the constant change in voltage to the coil and the no start? I cannot figure out why the voltage drops?

  • #2
    Ayuh,..... Welcome Aboard,..... Probably corroded wirin' connections,......

    Start at the battery, 'n clean to shiny metal, Clean, all of the wirin' connections,.....

    Pay attention to the Grounds, 'n both ends of the wires,.....


    • #3
      Cleaned all the battery connections and all the connections on the engine, so should be solid. Get 12v readings at the ignition switch and kill Switch. I do have a new ignition switch arriving today as the old one is pretty ugly, but I cannot understand how an ignition switch would only put out smaller voltage when turned on, if that is the issue?


      • #4
        Corrosion of any kind is a resistance, and resistance lowers voltages. This can happen on and in wires, and on and in connections like a key switch
        94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
        95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
        07 Seadoo GTX
        Merc Adults Only VP Adults Only
        G-Dad always said "First Liar doesn't stand a chance"


        • #5
          Don't forget the 20A fuse under the dash (feeds the key switch). It can get corrosion on the ends and become resistive.

          The world takes on a whole new perspective when viewed from 100’ below.
          1972 Bertram ‘Bahia Mar’ 20
          2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
          (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


          • #6
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            Yes, new ignition switch arrived and I put it in with new connectors. Now getting 12v on both sides of the coil and fires up every time. Never knew a ignition switch could do that. Thanks for the help.