4.3 Mercruiser won't start

[Gene W]

So I have a 1999 Bayliner Trophy 21' , 4.3 Mercruiser I/O tbi carb, 2 barrel. So here's my issues. Ran the boat out on the water and it quit running all of a sudden. Got it back home and found a loose wire at the coil. Replaced the end of the wire which plugs into the coil and the other end plugs into the distributor. Also replaced the distributor ignition module, no fix. Replaced the coil runs good. Quit a second time, had to be towed in. Replaced cap, rotor and new plugs, runs again. Out on the water quit again. This time replaced fuel pump and new filter/water separator. Come to find out no power at the pump. Added power from battery to pump, it runs. After long debates, rewired the pump to a switched power source at the rear of the motor. Now there's no spark, any ideas ?? My next step is to un do the wire by pass that I have done and see if that is where I lost my spark, or power to the coil.

 

[Rick Stephens]

You need to quit buying parts as your diagnostic method. Crazy. Do need to look at the electrical system as an essential safety mechanism to keep from blowing up on the water, let alone keep running. Be careful with jury rigging.

Purple wire is hot from ignition. Start there and trace it to components that get power from ignition (distributor, choke and oil pressure switch for the fuel pump)

If you don't have the correct Mercruiser Service Manual you will always have difficulty servicing your own motor and drive.

 

[Gene W]

Thanks for your input. It's been a bit of struggle. No where can I find a correct wiring diagram. Will keep looking, thanks

 

[Rick Stephens]

Wiring diagram is in the Mercruiser Service Manual #18 for your motor. Here's the likely main diagram. If you don't have the manual you are working blind.