4.3 mercuiser starts, stalls in 30 seconds

[vernonbluewater]

Starts right back up again, usually have to pump throttle to get it going, runs for 30-40 seconds then stalls again, repeat. I have been trying to figure this out for a while. Started by replacing oil pressure safety switch(mounts on oil pressure sending unit & cuts power to fuel pump if pressure drops below 4 psi). Getting voltage @ fuel pump on crank.(note- fuel pump gets voltage from battery on cranking but once running gets power from alternator) no luck. Pulled fuel tank supply tube, strainer @ bottom clean, replaced fuel filter, no luck. Replaced fuel pump, no luck.Checked carb on throttle pump, fuel squirting in - still no luck. Tried running off separate fuel tank in case of vapour lock or other issue with boat fuel tank - no luck. Bypassed oil pressure safety switch ( jumped wires together) - heard fuel pump turn on when turned on ignition - engine runs fine. Hooked safety switch back up - engine runs fine.Unhooked safety-engine starts to die-reconnect safety-engine comes back to life. Best I can figure is there was a bad connection. Tested boat in water for 4 hours yesterday-so I believe problem solved . Hope this helps someone with similar problem.

 

[Don S]

Re: 4.3 mercuiser starts, stalls in 30 seconds

Getting voltage @ fuel pump on crank.(note- fuel pump gets voltage from battery on cranking but once running gets power from alternator) no luck.

That is how a Volvo works, but you have a Mercruiser with an oil pressure switch that puts power to the fuel pump when the engine is running. It's located above the block mounted oil filter boss.

 

[vernonbluewater]

Re: 4.3 mercuiser starts, stalls in 30 seconds

The way I understand it is - yes the power goes thru the oil pressure switch - but on cranking power is supplied by battery & when running power is supplied by alternator.

 

[Don S]

Re: 4.3 mercuiser starts, stalls in 30 seconds

The way I understand it is - yes the power goes thru the oil pressure switch - but on cranking power is supplied by battery & when running power is supplied by alternator.

The alternator has nothing to do with power to the fuel pump on Mercruisers.
At cranking, the power to the fuel pump comes from the start solenoid on the Purple/Yellow wire.
When you let off the starter, that power stops also. But, when you let off the start switch the engine should be running and have oil pressure. Oil pressure closes the oil pressure switch and provides power to the pump.
Power to the pressure switch comes from the ignition switch, and also extends to the alternator as a sensing lead to turn on the alternator, But the power to the purple lead does NOT come from the alternator, it comes from the Ignition switch.

 

[vernonbluewater]

Re: 4.3 mercuiser starts, stalls in 30 seconds

Don S- Thanks for the clarification. The more I understand the boat the better I feel using it.