BMW E36 fuel pump and fuel pressure
What is the E36 fuel pressure specification and how is it measured?
The specification is 3.5 bar. The easiest way to measure the pressure is at the fuel system valve with a ready-made adapter. If you have no adapter, remove the pressure hose and connect the gauge in between with a T-piece.
How do I recognise a faulty E36 fuel pump?
The car does not start or runs poorly and the fuel pressure drops quickly. The cause can be an internal fault in the pump, for example loose vanes or a diaphragm, or wires that have come loose inside the pump unit. You can hear the pump hum briefly when the ignition is switched on, and it is easiest to check by lifting the pump out of the tank.
How do I find out whether the pump gets power?
The pump is under the rear seat on the passenger side. The relay is in the fuse box, and for the M3 conflicting information was given about the relay location; the right relay can be confirmed from the wire going to the pump. The pump can be tested by bypassing the relay and feeding power directly to the pump. A worn contact in the main relay can also cut the power.
Why won't the car start after a new pump?
Check that the pump pushes fuel in the right direction and that the wires are connected the right way round. For example, the terminals of a Bosch pump can be reversed compared with the original.