When there is enough fuel on the tank right (pump) side the suction of the inline pump alone should be enough for running the engine. If you can't hear either of the pumps running when you turn on ignition there is something wrong on the pumps' voltage supply. Both pumps have voltage supply from the same relay. On diesels the fuel pumps are running for 60 sec when ignition is turned to pos. 2 and shut out after that period if engine is not running.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey