elec. fuel pump question

[b0mbtrack]

i have a 5.0L Carbed. Ser. number OM674607 2003 thunderbolt V
My fuel pump doesn't turn on when i turn on the ignition. I checked the wire at the fuel pump (purple/yellow) and there is no power. I traced it to the elec. choke where there is also no power. I then traced it to a sensor that has something to do with oil (there are two right by eachother, one is big round and fat, the other just sticks straight out. It is that other one that has the purple/yellow wire going to it.) There is also no power to the purple/yellow wire at that oil sensor, but there is another wire going to that same sensor that is purple which there is power going to so i guess for some reason it is not going through the switch.
The question is can i just run a wire from the coil (+) to the choke and power everything up like that or will things not operate the way they are supposed to if i do that? I know if i do that the fuel pump will always be on with the ignition on which i don't think is normal.

 

[tommays]

Re: elec. fuel pump question

Unlike a car the pump ONLY gets power when your key is in the cranking position

After the motor starts the oil pressure switch keeps it running


Tommays

 

[b0mbtrack]

Re: elec. fuel pump question

thanks, i did see the Purple/yellow wire going to the oposite side of the solenoid attached to the starter.
There was also no power when the key was on Ignition but i couldn't check it on crank mode, although i will because i have alagator clips i can hook up to it to see my test light.
I'll have to then test all those same spots while the engine is running to see where in the chain it is loosing the power.

 

[b0mbtrack]

Re: elec. fuel pump question

Ok i did my tests.
When cranking i get voltage both at the oil pressure switch and at the other side of the starter and at the choke.
When engine starts power goes away in all those spots.
I do have good oil pressure though up at the helm, so my only guess would be that the sensor is bad..
Now what are the differances between the two sensors that are down there?

 

[Destin]

Re: elec. fuel pump question

Carbureted Mercruiser engines use the circuit below. The Purple/Yellow wire to starter provides power to fuel pump while cranking. The oil pressure switch keeps the fuel pump running after startup. You've probably got a bad oil pressure switch or connection.

 

[Bondo]

Re: elec. fuel pump question

Now what are the differances between the two sensors that are down there?

Ayuh,.........

1 is the oil pressure Sending Unit,........Which has usually 1 wire,........
And,......
The Other is the oil pressure Switch........... Which has the 2 wires you've observed........

 

[b0mbtrack]

Re: elec. fuel pump question

thank you all for very good and fast answers!!!!!!

 

[Destin]

Re: elec. fuel pump question

After further thought, you should have power on the Purple wire and choke with the ignition on all the time, otherwise the ignition switch could be bad, or the emergency cutoff switch is activated, or a bad connection somewhere else.