# Fuel system diagnosis

#### Fuel pump not running.

Check fuse 11 (7.5A). OK ?

##### NO

Replace fuse. If no power to fuse, check fuel pump relay.

##### YES

Connect volt meter to both wires of pump. Crank engine. Battery voltage present ?

##### NO

Check resistance from brown wire to ground. Approx. 0 Ohms ?

##### NO

Repair wire

##### YES

Replace pump

Check green/violet wire resistance from pump to pin 87a on fuel pump relay connector, with relay removed. Approx. 0 Ohms ?

##### NO

Repair wire

#### Fuel pump running only during start

Remove fuel pump relay, check voltage between terminal 30 and ground. Battery voltage ?

##### NO

Check and repair 1.5mm red wire from relay to battery junction block or battery in engine bay.
NOTE : Some models take power from the main relay. In these cars, check operation of main relay

##### YES

Check voltage from pin 86 to ground with ignition on. Battery voltage ?

##### NO

Check operation of main relay. Check and repair the 0.5mm red or red/white wire from pin 87 of main relay

##### YES

Check voltage between pin 85 to battery power. Crank engine. Battery voltage ?

##### NO

Check appropriate wiring diagram for ground source. M10 uses starter to ground relay, all others use the DME to trigger relay.

##### YES

M10 only, others skip this step : Check speed signal wire resistance between pin 1 of fuel pump relay and ground. Approx. 0 Ohms ?

##### NO

Check and repair 1.5mm black wire from pin 1 to terminal 1 on coil.

##### YES

Replace fuel pump relay

#### Fuel pressure low or high

Check pressure by installing fuel pressure gauge inline on fuel feed hose, fuel feed hose does NOT go to fuel pressure regulator.

##### LOW

Check or replace fuel filter (low pressure), check for obstructions or damage to fuel lines. OK ?

##### NO

Repair or replace faulty component.

Note : Fuel pump works at approximately 100psi. It is highly unlikely that a running pump will not be able to deliver specified fuel pressure.

##### YES

| Replace fuel pressure regulator.

E30 M3 Repair Manual V2.7. Copyright ©1999-2001 Koala Motorsport & Brett Anderson