BMW E30 fuel pump not running or getting no power
E30 fuel pump not running – what usually causes it?
The most common causes are a faulty pump relay, a blown fuse or a break in the wiring. An internal crack in the relay is common even if the relay and fuse look fine. A missing relay ground also cuts the pump's power. Connectors often oxidise, so measure the voltage at the end of the wire, not at the connector.
Why does the pump on an injected model not run even though the engine turns over when cranking?
On injected models, the engine control unit runs the pump only when it receives a signal from the crankshaft position sensor. If there is no signal, the pump does not run. So check the relay, fuses, grounds and the crankshaft sensor. The pump normally buzzes briefly when the ignition is switched on.
How do I test the fuel pump?
1. Feed 12 V directly to the pump. If it runs, the fault is in the relay or wiring. 2. Measure the fuel pressure with a pressure gauge. 3. Alternatively, measure how much fuel comes out of the hose per minute and compare it to the value in the repair manual. Fuel coming out of a disconnected hose alone does not prove the pump is good, because a weak pump can deliver fuel but not pressure.