BMW E39 M57 transfer pump and transfer pressure
What does the transfer pump do in the E39 M57 diesel?
The pump in the tank lifts the fuel to the transfer pump under the driver's seat, which raises the pressure to suit the high-pressure pump. With the key in position 2, the pumps should run for about 60 seconds even if the car is not started.
What is the correct transfer pressure on the E39 M57?
Sources vary: according to one, the pressure should be 2-3.5 bar, according to others about 4 bar. The pump in the tank gives the transfer pump a pre-pressure of about 0.5 bar. A pressure of 0.97 bar means the transfer pump is not working.
Why does the E39 diesel not start when the transfer pump does not run?
First check whether you can hear the pumps from under the seat and from the tank after switching the power on. If the pump does not run, the cause can be the transfer pump relay K96 behind the glove box (part number 61368373700). Sometimes it is only a poor contact in the relay.
How do I know the pump in the tank must be replaced?
A constant noise from the tank while the power is on means the pump must be replaced. Gurgling and the fuel lines draining after shutdown point to air getting into the suction side.