Engine/Transmission (1998.5 - 2002) Someone please explain the lift pump/fuel pump relationship

[tajensen]

There has been much discussion recently concerning both the fuel and lift pumps. I have a vague understanding of their respective functions, but not enough knowledge to explain much of anything to another person. If some of you would share your knowledge, I would appreciate it.

 

[jkern]

the term lift pump and fuel pump are generally used interchangebly to describe the device that moves fuel from the tank to the the injector pump also know as the VP44. hope this helps clear things up a bit.

 

[Oil Burner]

Lift pump supplies fuel to the VP44 injection pump. Some of the fuel is pumped by the VP44 to the injectors but some fuel is used to cool and lubricate the VP44. Some people have added other fuel pumps (pusher pumps) to replace or assist the lift pump in supplying fuel to the VP44.



-Jason

 

[illflem]

The lift pump, more commonly known as a transfer pump pumps fuel at low pressure, 7 -15 psi to supply the injection pump. The injection pump in turn increases the pressure upwards to 17,000 psi to supply the injectors.

 

[RADdodge]

Also, the VP-44 injection pump has an internal pump to supply the injector side of the pump. That is why some have seen negative pressures (Big Saint for one) when their Lift Pump died. As has been mentioned before, the pumps job is to pump, not suck. The lift pump sucks as a result of the tank being too far away and below its location on the engine. Also, when the fuel level in the tank goes down, the pump has to work harder to get the fuel from the tank. Since the fuel lubricates the pumps, fuel starvation also equals lubrication starvation. As a result of all this, some have opted to either relocate their lift pump back by the tank to alleviate the suction problem, or they have added a pusher pump.

 

[tajensen]

Thanks for the clarification guys.