Mercruiser 5.0 W thunderbolt V fuel issues

Hello fellas.. I'm new to the forums, I own a 2003 Bayliner 2150 with this engine..
I'm having some fuel issues after I let the boat sat for 4 years. ()
I cleaned the carbs... But I'm having issues with the fuel pump..
I'm not sure how the fuel system works,
The engine does not stay running for long in iddle and when it start, if I accelerate.. It dies with I a few seconds..

Well back to the fuel and electric fuel pump..
I sent 12v directly to it and it pumps 9 psi of pressure so.. According with the manual is good..

But I don't hear the pump while the engine is running, only when I crank the engine works for a second until the actual engine starts.. As soon as I let go the key the electric fuel pump stop pumping..
So my NOOB question is.. That's the way this low pressure pump are supposed to work? Remember that my engine has the 2 barrel carb,
My background :I'm a mechanic aficionado, I can work in new and old cars and motorcycles..
But this is my first boat and I didn't have time to play with it. Before I stopped like 4 years ago.. Ran fine for 2 seasons, when I bought the boat I cleaned the carb too and it worked like a kitty, ran smooth and fast for 2 summers

Any help and guidance will be much appreciated it

Electric fuel pump gets power two ways
1. When cranking off the starter
2. It gets 12 v through an oil pressure switch when running, common failure item. If engine stalls/key left on oil pressure will drop below 4 psi and cut power to the pump

If it stops when key is in run likely oil pressure switch is dead. Easy fix

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Spiderman3k said:

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Well back to the fuel and electric fuel pump..
***I sent 12v directly to it and it pumps 9 psi of pressure so.. According with the manual is good..
I think that 9 psi is a bit high. But if the inlet needle/seat is holding.... then you are likely OK.

But I don't hear the pump while the engine is running, only when I crank the engine works for a second until the actual engine starts.. As soon as I let go the key the electric fuel pump stop pumping..
I believe that the fuel pump's power is supplied by a relay.
The relay is then triggered by two means:
..... the start-bi-pass circuit (the relay is momentarily triggered by the starter motor's solenoid circuit) and provides fuel prior to oil pressure coming up.
..... the N/O (normally open) Low Oil Pressure switch once engine oil pressure reaches/exceeds X oil pressure (some suggest 4 psi, some say 7 to 8 psi).

Any help and guidance will be much appreciated it
Perhaps temporarily install an indicator light in fuel pump's circuit.
Watch to see if the light glows during cranking (of which it should since you mentioned that above).
Now watch to see if the light continues to glow once the starter motor is disengaged and after the engine is operating for the few seconds that it does.

If the light does not glow once the engine fires up, then test the N/O LOP Switch.
Using your method above ***, you should be able to fill the carburetor's float bowl and keep the engine running at idle long enough to test the N/O Low Oil Pressure switch.

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