Fuel Pump Inspection

GENERAL INFORMATION

The fuel pump is located in the fuel tank.

CAUTION

Do not use open flames, smoke, or hold any hot objects near the work area. There is a risk of accident! Keep a fire extinguisher ready. Make sure the work area is properly ventilated. Fuel vapors are toxic. The fuel system is under pressure. Fuel may spray out under pressure when the system is opened. Catch fuel with a cloth. Wear protective goggles.

Test conditions: The battery must be fully charged; voltage must not be less than 11.5 V. CHECKING VOLTAGE SUPPLY

PROCEDURE

1. Check fuel pump fuse No. 28. Replace a faulty fuse.

2. Briefly engage the starter. The fuel pump must start running, which should be audible for approximately 1 s. If ambient noise is high, ask an assistant to listen.

3. If the pump does not run, connect the remote control.

4. Press the remote control switch. If the pump now runs, check the fuel pump relay.

If the pump does not run, proceed as follows:

5. Fold down the rear seat and remove the cover of the fuel level sender and fuel pump.

6. Disconnect the connector of the fuel level sender and fuel pump.

7. Connect a diode test lamp or a voltmeter to both outer contacts of the plug.

8. Switch on the remote control. The measuring instrument must show battery voltage (approximately 12 V). If it does not, there is an open circuit. Locate it using the wiring diagram and repair it.

9. If the instrument shows battery voltage, remove the fuel reserve sensor.

10. Check whether the flange and the fuel pump are connected by electrical wires and whether the connection makes good contact. Use an ohmmeter and auxiliary wires to check for an open circuit between the sensor housing and the fuel pump. If necessary, repair the damage.

11. If there is no open circuit, replace the fuel pump.

12. Install the fuel pump and the reserve sensor, and connect the electrical wires.

FUEL PUMP OUTPUT CHECK

PROCEDURE

1. Remove the fuel tank cap to release fuel pressure.

CAUTION

The fuel system is under pressure! Before opening hose connections, place a thick rag over them. Then carefully open the hose and release the pressure. Wear safety glasses while doing so.

2. Disconnect the fuel return hose from the fuel distribution line by pressing the release button of the quick-release connector. 1 – fuel supply line.

3. Connect the auxiliary hose with the intermediate element to the fuel return line from the engine, and lower it into the measuring container.

4. Connect a voltmeter to the battery.

5. Press the remote control switch for 15 s. While doing so, read the indicated battery voltage and record it.

6. Compare the pump output with the required value in the chart.

Example: During the check, battery voltage is 12.5 V. Since the voltage at the fuel pump is 2 V lower than battery voltage, the voltage at the fuel pump is 10.5 V (12.5 – 2 = 10.5). This voltage corresponds to a pump output of approximately 130 cm3/15 s.

*) Minimum output, cm3/15 s. **) Voltage at the fuel pump with the engine off and the pump running (approximately 2 V lower than battery voltage).

7. If the supply voltage is correct but the output is still low, check the fuel lines for damage or blockage.

8. Check whether the fuel filter is clogged. To do this, repeat the output check with a new fuel filter.

9. If the minimum output is still not reached, remove the fuel delivery unit and check whether the filter screen is clogged. If necessary, clean the screen.

10. If the fault is not found, check the fuel pump check valve (work to be performed at a dealer service station).

CAUTION

If minimum pump output is achieved but a fuel supply fault is still suspected (e.g. intermittent fuel supply interruption), check the pump current consumption with an ammeter. Specified value: max. 8 A. If the current is higher, replace the fuel pump. For intermittent fuel system faults, the test can be performed while driving. An assistant is required for this.

11. Disconnect the remote control and reinstall fuse No.

28.

12. Install the fuel tank cap.

13. Reinstall the rear seat.