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Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

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  • Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

    I just bought a 1999 Bayliner Trophy with a Mercruiser 4.3L V6 engine. I bought the boat from a Marine Dealer in Mississippi that supposedly had the engine and carburetor rebuilt. The day after I received the boat here in San Diego, CA, I started and ran the engine for 5 mins or so. It sounded weird when I started it almost like a few teeth missing on the flywheel. 5 days later I took it down to the launch ramp and it wouldnít start. I replaced the lug on the hot lead (RED) that bolts ot the starter and the battery. I also replaced the starter with a new one. This starter came with a new solenoid too. Then the engine turns over SLOWLY and does not sound smooth when turning over. It still wont start. It almost sounds like the mesh of the gear with the starter and flywheel ring gear are not meshing 100%.

    A week later, I called Sunset Marine here in San Diego and the mechanics said to pull out all the plugs, you may have water in one or some of the cylinders. I did that and found no water at all. I put the original starter back it after testing it. The starter spins fine. I checked the firing order too. I charged both batteries over 2 nights. Batt#1 has 550 cold cranking amps (CCA's), Batt#2 has only 405 CCA's. I verified everything and it tried it again. It still turns over SLOWLY like its a torquey 1500 HP engine. Then after 2 mins of trying to start it, the batteries wont turn it over at all. I donít get it. The engine acts as if it has trouble turning over. Now the solenoid just clicks like the batteries are almost dead. Both Batteries have 13.2-13.5 Vdc when trying to start it...then 12.7 after 2 mins..... Very weird that it wont start.

    The next thing I am going to do, is get one new battery with 675 CCA's and then pull the distributor to rule that out, pull all the plugs out again and manually turn the crankshaft/harmonic balancer over by hand with a breaker bar to see how freely she turns. It's possible that maybe the distributor jumped a tooth? But who knows??? I dont know, this is very frustrating. I am still scratching my head.

    What do you guys recommend I try? Am I overlooking something here?


    Attached Files

  • #2
    Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

    A 550 CCA battery should turn that motor fine. How are the battery cables and ends? Maybe put some jumpers from the battery to the block and starter to see how it spins then. Those cables aren't too much money, you might just do them as a guess.
    If the cables are good, it could be mis timed, or the timing chain could have jumped a tooth. Is it definitely in neutral?
    Try spinning it over with the spark plugs out.
    How does the engine oil look?
    87 Formula F223LS, 97 Alpha Gen II, 97 Thunderbolt V Ignition, 2016 383 Stroker
    Lake Winnipesaukee, NH


    • #3
      Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

      Well I can't speak for electrical issues on boats but I can speak to what I experienced less than a month ago with my car. I had to pull the transmission and when I put it back I forgot to bolt back in a major ground strap that powered the alternator, starter, and who knows what else. The vehicle made it 3 miles before the battery completely drained, since that was all that was powering the car.

      You mentioned they just rebuilt the engine, so in the process they had to unhook the wiring harness completely. Could it be they didn't hook up a ground properly? I'd sniff around the wiring just to be sure.


      • #4
        Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

        Like NHGUY said, I would suspect cables. EVEN if the connections are clean and shiny, they may be corroded UNDER the crimped on connectors. I chased that gremlin a few years back. Its easy and cheap to rule that out. Get some new crimp on connectors from the auto parts store, cut off the old connectors, and crimp on the new ones. Then cross fingers ...


        • #5
          Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

          My 96 4.3 does that now, but with a battery charge I can get it spinning over fast enough to fire the engine. It is likely cables. At first I thought it was the starter, but cleaning of the cables helped, although I need to do some more cleaning or replacement of the cables. One of my planned winter repairs.
          I might try a shim on the starter to give it just a little space between the gears of the flywheel also.

          1996 Rinker Flotilla, 4.3, 1998 Seadoo GSX Limited, 1995 Hydra 24' Pontoon, 70hp Force, 1995 16' Alumacraft Jon boat, 25hp 'Rude, 1968 Fibra with Volvo stern drive, and various other boats used for parts.


          • #6
            Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

            I'll assume you already cleaned the positive and negative cables at both ends since you've had them off the battery and starter. Someone else just suggested the main ground cable where it attaches to the block, so you did that too. If that didn't fix the problem, start isolating the issue with a volt meter and an apprentice.

            Make sure the battery is charged overnight before getting started. That should take it to around 13 volts before you turn anything on that uses the battery. Attach your volt meter negative to the case of the starter and the positive to the copper stud the battery cable attaches to. Have the apprentice start cranking while you watch the meter. While cranking (or attempting to crank) the voltage should be somewhere in the range of 8-10 volts. If it's still up around 12V the starter isn't doing it's job. If it's less than 8V you have a problem in the circuit.

            Starters rarely fail like that, so I'll assume you have too low a voltage and move on to isolate where the voltage is dropping. A wire that is doing it's job will have little or no measurable voltage measure between the ends. If the wire is bad or a connection at the end is bad, a voltage shows up just like water pressure in a stopped up pipe. In the following checks, there should be little or no voltage measured. A measurement over a volt means a problem.

            To eliminate the ground as an issue, connect the negative lead of the meter to the negative battery terminal and the positive lead to the case of the starter. When your apprentice cranks, there should be less than 1 volt measured. If it's more than that, start working back toward the battery - move the meter lead from the starter case to the block, then the cable terminal at the block, then the cable terminal at the battery. Somewhere in there you will find a bad connection or a bad cable.

            Now do the same thing with the positive terminal of the meter on the positive battery terminal and start working back along the wires with the negative meter probe. You will go from the starter stud to the wire terminal to the other end of the wire, the solenoid terminal, the other solenoid terminal and to the battery.

            Somewhere in there you will almost always find a bad cable terminal or just a corroded one that needs cleaning. Bad solenoids are also common and fairly cheap.

            Hope this helps,



            • #7
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              Re: Mercruiser 4.3L V6 engine WEIRD starting problem (HELP)

              pull all plugs out and then select forward.go to rear of boat and you should be able to turn the engine over fairly freely with the prop.if th engine is struggling to rotate the engine and drive may be out of alignment but as the dealer has already proved they are not reputable and have left what could be a an expensive trouble shooting experience.a have a 1000 cca 120 amp battery for a 5 litre as the boat cannot be towed as in a car as easily.if its very slow in turning the engine over some more investigating on compression,timing and engine alignment to know where to start.the pistons have to suck the fuel in and a slow mturning engine is doing u no favours.