BMW E65 diesel stalls or will not start - rail pressure too low
E65 730d will not start or stalls while driving and rail pressure is too low - what could be the fault?
Rail pressure is the pressure in the high-pressure fuel rail. If it stays low, the cause can be that the fuel pump in the tank is not getting a run command. Replacing the fuel filter does not usually fix this.
What controls the E65's fuel pump and how is the fault revealed?
The pump's rotation speed is controlled by the satellite control unit in the right B-pillar with a pulse signal. If the pump does not start but runs when power is applied to it directly, the fault is in the control and not in the pump. Replacing and coding the satellite control unit has fixed this.
Can a main relay fault cause the same symptom?
Yes. Replacing the engine control main relay has eliminated starting problems and symptoms for a long time. Many different bus codes can appear in the fault memory even though the fault is only in the relay, so the codes do not show the cause. Long cranking also strains the battery.
What else can be behind the rail pressure dropping?
The cause can also be injector leak-off, the high-pressure pump or poor contact in the pressure sensor connector. A leak-off test tells more than the correction values alone. The exact cause depends on the car, so troubleshooting is best done with a diagnostic tool.