Fuel Pump, Checking

Fuel Pump, Checking

=> [ Function and Voltage Supply, Checking ]

=> [ Delivery Quantity, Checking ]

=> [ Current Draw, Checking ]

=> [ Fuel Pump Check Valve, Checking ]

Special tools, testers and auxiliary items required

• Pressure Tester (VAS 6550)

• Remote Control (V.A.G 1348/3A)

• Test Instrument Adapter/DSO (5-pin) (VAS 5565)

• Multi-Meter (V.A.G 1715)

• Wrench (T10202)

• Torque Wrench (40-200 Nm) (V.A.G 1332)

• Voltage Tester (V.A.G 1527B)

• Vehicle Diagnostic Tester

• Measuring Container, 3 liter

Function and Voltage Supply, Checking

• Battery voltage at least 11.5 volts

• The fuse for the fuel pump is OK.

• The output diagnostic test mode checks the fuel pump.

- Connect the vehicle diagnostic tester as follows:

- Connect the diagnostic cable - 2 - to the Data Link Connection (DLC) inside the drivers footwell.

- Turn on the ignition.

- Press the buttons for "Vehicle Self-Diagnosis", "01 - Engine electronics" and "Output Diagnostic Test Mode (DTM)" on the display in succession.

- Press the right arrow button on the display to initiate the fuel pump activation.

The fuel pump must run.

• The fuel pump runs quietly.

- Turn off the ignition.

If the Fuel Pump Does Not Run:

- Remove the rear bench seat.

- Remove the cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- First, pull on the connector - arrow - without pressing the retainer to make sure it connected securely. If the connector was not connected correctly, check the fuel pump function again.

- Disconnect the connector.

- Check the contacts on the connector and the fuel delivery unit for damage.

- Install the test instrument adapter/DSO (5-pin) (VAS 5565) between the connectors on the fuel delivery unit and cover.

- Connect the voltage tester (V.A.G 1527 B) to the wires - 1 and 5 - on the test instrument adapter/DSO (5-pin) (VAS 5565).

- Turn the ignition on.

• The Light Emitting Diode (LED) must light up briefly.

If the LED does not light up briefly:

- Locate and repair the open circuit in the wiring using the wiring diagram.

If the LED lights up briefly (the voltage supply is OK):

- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.

- Check if the electrical wiring between the flange and fuel pump are connected.

If no open circuits are found:

- The fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.

Delivery Quantity, Checking

• Voltage supply is OK.

• The fuel pressure regulator and residual pressure is OK. Refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.

• The fuel filter is OK.

- Remove the fuel cap from the fuel filler tube.

- Remove the rear bench seat.

- Remove the cover - 1 - from fuel delivery unit. The arrow - 2 - points in the direction of travel.

- First, pull on the connector - arrow - without pressing the retainer to make sure it connected securely. If the connector was not connected correctly, it could cause a fault.

- Connect the remote control (V.A.G 1348/3A) to the test instrument adapter/DSO (5-pin) (VAS 5565) and to battery positive (+).

• This step allows the fuel pump to run when the engine is not running.

• The delivery rate of the fuel pump is measured at 4 bar. Therefore, measure the fuel pressure before measuring the delivery rate. Refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.

The fuel system is under pressure!

• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.

• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.

- Disconnect the return line - 1 - from the fuel pressure regulator.

• Press in the securing ring to disengage the fuel line.

- Install the adapter (VAS 6550/1) to the fuel pressure regulator and hold the other end of the adapter in a measuring container.

- Operate the remote control (V.A.G 1348/3A) approximately 5 seconds in order to fill the fuel filter.

- Empty the measuring container.

- The fuel pump delivery rate depends on the voltage. So, connect the multi-meter (V.A.G 1715) to wires - 1 and 5 - on the test instrument adapter/DSO (5-pin) (VAS 5565).

- Operate the remote control for 60 seconds and simultaneously measure the voltage of the fuel pump.

- Compare the quantity of fuel delivered with the specification.

*) Minimum delivery rate cm3/60 s

**) Voltage of the fuel pump with engine running in idle and the pump is on.

Example:

During the test, a voltage of 10.5 volts is measured. This results in a minimum delivery quantity of approximately 1200 cm3/60 s.

If the minimum delivery rate is not attained:

- Check the fuel filter as follows:

The fuel system is under pressure!

• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.

• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.

- Disconnect the fuel supply line - arrow - from the fuel filter.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the adapter (VAS 6550/1). Hold the other end of adapter (VAS 6550/2) in the measuring container.

- Make sure the drain is closed and the shut off levers are open.

- Operate the remote control (V.A.G 1348/3A). Slowly close the shut off lever - A - until the pressure gauge reads 4 bar. From this point on do not move the position of the shut off lever.

- Empty the measuring container.

- Repeat the fuel delivery test.

If the minimum delivery rate is now obtained:

- Replace the fuel filter.

If the minimum delivery rate is again not obtained:

- Remove the fuel delivery unit and check the fuel strainer for contamination.

Only when up to now no malfunction has been detected:

- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.

- Reconnect all disconnected fuel lines.

- Bleed the fuel supply system. Refer to => [ Fuel System, Bleeding ] Service and Repair.

Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply, for example sporadic loss of fuel supply:

- Check the fuel pump current draw. Refer to => [ Current Draw, Checking ].

Current Draw, Checking

- Remove the rear bench seat.

- Remove the cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- First, pull on the connector - arrow - without pressing the retainer to make sure it connected securely. If the connector was not connected correctly, it could cause a fault.

- Connect the current clamp - A - to the red wire of the test instrument adapter/DSO (5-pin) (VAS 5565) with the word "current clamp" on it.

- Start the engine and run at idle speed.

- Measure the current draw of the fuel pump.

Specified value: Max. 9 amps.

• If the malfunction in the fuel system is sporadic, the test can also be performed during a road test, but a second person is required.

If the current draw is exceeded:

- The fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.

Fuel Pump Check Valve, Checking

- Remove the rear bench seat.

- Remove the cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- First, pull on the connector - arrow - without pressing the retainer to make sure it connected securely. If the connector was not connected correctly, it could cause a fault.

- Connect the remote control (V.A.G 1348/3A) to the test instrument adapter/DSO (5-pin) (VAS 5565) and to battery positive (+).

The fuel system is under pressure!

• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.

• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.

- Disconnect the fuel supply line - arrow - from the fuel filter.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the adapter (VAS 6550/1). Hold the other end of adapter (VAS 6550/2) in the measuring container.

- Close the shut off lever - A - on the pressure tester (VAS 6550) so the lever is perpendicular to the direction of flow.

- Operate the remote control in short intervals, until a pressure of approximately 4 bar has built up.

Danger of spraying when opening the shut off lever; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold the container in front of the free connection of the pressure measuring device.

- If pressure builds up too high, lower the excess pressure by carefully opening the shut off lever.

- Watch the pressure decrease on the pressure tester.

• After 10 minutes the pressure must not drop below a 3 bar decrease.

If the pressure drops further:

- Check the line connections for leaks.

If no fault is detected in the wiring:

- The fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.