Fuel pump troubleshooting

This can be used to check whether the fuel pump is delivering fuel: at the connector location on the left next to the shock absorber strut (shown here on a vehicle with KE-III-Jetronic injection), disconnect the fuel supply line (2). Attach hose (1) to the supply line and place its free end into a suitable container.

3 – fuel return line;
4 – vent line from fuel tank to activated charcoal canister.

PROCEDURE

First check the fuse (refer to Body Electrical System chapter).

If the fuse is good, continue with the following:
Sometimes it is possible to determine by listening whether the fuel pump is operating: listen under the vehicle at the fuel tank height for the fuel pump running while an assistant turns the ignition on.

If operating noise is heard, the pump is probably good. If nothing is heard, check whether fuel is being delivered:
Models with 4-cylinder engine and Mono-Motronic injection: disconnect the line leading to the fuel injection unit at the threaded connection. Attach an extension to the hose coming from the fuel tank and place its end into a suitable container.

An assistant must crank the engine with the starter during this time. Fuel should now be delivered.

Models with 4-cylinder engine and Digifant injection: disconnect the supply line at the front of the fuel distributor pipe, attach an extension hose and place the free end into a suitable container.

An assistant must crank the engine with the starter during this time. Fuel should now be delivered.

Models with 5-cylinder engine and KE-III-Jetronic injection: loosen the threaded connection on the fuel supply line – keep a rag ready to wipe up escaping fuel.

Even with the engine not running, a small amount of fuel should now emerge, because the fuel system is under pressure due to the fuel accumulator.

If nothing emerges, an assistant must crank the engine with the starter.

The fuel pump should now begin delivering fuel.

All models: if nothing moves, check the multi-pin connector at the top of the fuel tank sending unit flange and determine whether the pump is receiving power:
Remove the luggage compartment mat.

Remove the black metal cover.

Disconnect the multi-pin connector.

Using a voltmeter or test lamp, check whether approximately 12 V is present between connector pins 1 and 4 (brown and green-yellow wires). For this measurement an assistant must crank the engine with the starter (gear selector in Neutral, vehicle with parking brake applied).

If the pump does not run even though power is supplied, the pump is defective (remove and replace).

If no power is supplied, the fuel pump relay in the central control unit is suspected. Its testing is described in the chapter Body Electrical System.

Other possible causes are: defective wiring to the relay or pump, clogged or kinked fuel line hose, clogged fuel pre-filter or fuel accumulator.