7.4L Volvo fuel pump wiring issue

[Bayliner 454]

Hi All,

Hoping someone can shed some light on my issue. Have a 74glplkd carbied engine production number 3868626. Have been having fuel problems with it and have been right through the system and come up with the following issue.

Electronic in line Fuel pump is supplied power via a relay only on crank ie will only power the pump when you are turning the engine over. On the switching side of the relay there are two wires coming in to it. My question is should this relay have power to the switching side from and ignition source (key, alternator, ignition module) so the pump will run when the engine is running or the key has ignition on.

Currently pump needs to lift fuel approx 2 ft to carby. Engine runs perfectly until you get to approx half a tank or earlier in rough seas and then seems to starve for fuel. Take it head pressure in the tank keeps fuel up while the tank is resonable full. I have run back from the reef twice now on jeery cans mounted above the carby level and engine doesn't miss a beat.

Should this pump run all the time and if yes where does the power supply come from??

Any help would be greatly appreciated.

 

[Don S]

Re: 7.4L Volvo fuel pump wiring issue

Should this pump run all the time and if yes where does the power supply come from??

Yes it run any time the engine is running. It picks up power from the alternator engaging the relay.

The pump should have no problem pulling fuel up.to it, unless there is an air leak in the system NOTE: The fuel tank and fuel system from the tank to the pump are NOT Pressurized.
It sounds like you may have a crack in the fuel pickup tube inside the tank. Once the level gets below half the crack is exposed and the pump sucks air instead of fuel.

Here are some tests you can do on the fuel system.
http://forums.iboats.com/showthread.php?t=167561

 

[Bayliner 454]

Re: 7.4L Volvo fuel pump wiring issue

Yes it run any time the engine is running. It picks up power from the alternator engaging the relay.

The pump should have no problem pulling fuel up.to it, unless there is an air leak in the system NOTE: The fuel tank and fuel system from the tank to the pump are NOT Pressurized.
It sounds like you may have a crack in the fuel pickup tube inside the tank. Once the level gets below half the crack is exposed and the pump sucks air instead of fuel.

Here are some tests you can do on the fuel system.
http://forums.iboats.com/showthread.php?t=167561

Thanks Don S, I have already been right through the fuel system as I was on the same track with the pick up. Has a plastic tube on the pick up and all good. Had narrowed it down to no power to the pump with ignition on. Just wanted to clarify that it should run all the time and where the power supply was from. Thought that it may have also come from the ignition module or coil.

Sounds like I have a wiring issue. I have noted that there is a green wire from one of the posts off the alternator which has no output at all at any time and also a green wire that comes in to the switching side of the fuel pump relay. Have checked continuity from relay plug to alternator (green wire ) and got nothing. Not sure if this is due to a diode in the wire or what. I am going disconnect the wire and recheck. Will also check the circuit breaker for the pump as it may be u/s even though it is not tripped??

Thanks again for your help, much appreciated.