Signs of a failing Oil Pressure Switch

[f575gtc]

Hello all,

I have a 2004 4.3L mercruiser and from my understanding, if I turn the key to the ON "Running" position, the fuel pump should not prime, it should only prime when the engine is cranking before it starts and once there is more than 4 psi of oil pressure and the oil pressure switch intercepts the starter signal and takes over.

My issue is that when I turn the key to the on position before cranking, the buzzer under the dash will turn off, the fuel pump will randomly prime for 2-3 seconds then stop and the buzzer comes back on. This is completely random, sometimes I can turn the key on and off a few times and it won't do it, sometimes the fuel pump will run for a few seconds then stop.

Once the engine starts, the engine stays on and runs, if I jump the two oil pressure switch pins on the plug the pump stays on continuously and if I unplug it while the engine is running you can see the fuel stop.


Does this sound like a bad oil pressure switch, a bad ground somewhere, or possibly a bad ignition? I can't imagine it being the ignition because if it sent a cranking signal to the fuel pump it should also send it to the starter yet the start never cranks in the ON position only the fuel pump kicks on.


Thanks

 

[Bt Doctur]

I have a 2004 4.3L mercruiser and from my understanding, if I turn the key to the ON "Running" position, the fuel pump should not prime, it should only prime when the engine is cranking before it starts and once there is more than 4 psi of oil pressure and the oil pressure switch intercepts the starter signal and takes over

Only on a carb`d motor. fuel injection primes for 2 seconds then stops

Once the engine starts, the engine stays on and runs, if I jump the two oil pressure switch pins on the plug the pump stays on continuously and if I unplug it while the engine is running you can see the fuel stop.

From where do you see fuel?

 

[f575gtc]

Sorry my 4.3L is still carbureted not fuel injected, we bypassed the fuel tank and ran a clear tube from an auxiliary tank to the fuel inlet.

 

[Bt Doctur]

Ok, items turning on and off may be a sign of a backfeeding ground. The electric fuel pump should not operate with the key "on" .The pump will work from the starter solenoid in the "start" position, and then go to the switched 12v from the ign system using the oil pressure switch.

 

[Bondo]

My issue is that when I turn the key to the on position before cranking, the buzzer under the dash will turn off, the fuel pump will randomly prime for 2-3 seconds then stop and the buzzer comes back on. This is completely random, sometimes I can turn the key on and off a few times and it won't do it, sometimes the fuel pump will run for a few seconds then stop.

Ayuh,..... Welcome Aboard,.... Startin' at the battery, clean all the connections to shiny clean metal, reassemble, then coat 'em with grease,.......

Especially All the grounds to, 'n on the motor,....

 

[alldodge]

I think you have either a key switch that is not making a positive connection, a 10 pin connector with connection issues and /or in conjunction with a oil pressure switch that is intermittently making connection. The oil pressure switch passes 12V and the ground is always there.