Engine MFI
Fuel Pump, 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)
• Hand Held Multi-Meter (V.A.G 1526D) with Current Clamp (V.A.G 1526B/2)
• Wrench (T10202)
• Torque Wrench (40-200 Nm) (V.A.G 1332)
• Measuring Container, 2 liter
• Vehicle Diagnostic Tester
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Delivery, Checking ]
=> [ Current Draw, Checking ]
=> [ Fuel Pump Check Valve, Checking ]
Function and Voltage Supply, Checking
• Fuel Pump (FP) relay (J17) OK
• Battery voltage at least 11.5 V.
• Fuel pump fuse OK, fuse assignment, refer to.
• FP function is checked via output Diagnostic Test Mode (DTM).
- Connect the vehicle tester as follows:
- Connect the diagnostic cable connector to the Data Link Connector (DLC) in driver's footwell.
- Turn on the ignition.
- Press the Vehicle Self-Diagnosis, Engine Electronics and Output Diagnostic Test Mode buttons on the display.
- Press the right arrow button > on the display to initiate fuel pump activation.
The fuel pump must run.
- Switch off ignition.
If FP does not start up
- Remove the rear seat bench.
- Remove the cover from the fuel delivery unit.
- 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.
- Connect the (VAS 5565) to the connector on the cover and on the fuel delivery unit.
- Connect a (V.A.G 1526D) to the wires - 1 and 5 - on the (VAS 5565).
- Start the output DTM again and measure the voltage at the fuel pump.
• Specified value: approximately 2 volts less than battery voltage.
Voltage Supply not OK
- Locate and repair open circuit in wiring using wiring diagram.
Voltage Supply OK
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the connection wrap a cloth around the connection. Loosen the connection carefully to release the pressure.
- Remove the fuel lines - 1 and 2 - from the flange.
• Press in the securing ring to disengage the fuel lines.
- Remove the locking ring using (T10202).
- Check whether electrical wires between flange and FP are connected.
If No Open Circuits are Found
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
Fuel Delivery, Checking
• Voltage supply OK.
• Fuel pressure regulator and residual pressure OK, checking, refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.
• Fuel filter OK.
- Remove the rear seat bench.
- Remove the cover from the fuel delivery unit.
- 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.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Connect the (VAS 5565) to the connector on the cover and on the fuel delivery unit.
- Connect the (V.A.G 1348/3A) to the (VAS 5565) and to the battery positive (+).
• This step allows the fuel pump to run when the engine is not running.
• The fuel pump delivery rate is measured at 4 bar. Measure the fuel pressure before measuring the delivery quantity. Refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the connection wrap a cloth around the connection. Loosen the connection carefully to release the pressure.
- Disconnect the return line - 1 - from the fuel pressure regulator.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550/1) to the fuel pressure regulator and hold the other end in a measuring container.
- Operate the (V.A.G 1348/3A) approximately 5 seconds to fill the fuel filter.
- Empty the measuring container.
- The fuel pump delivery rate depends on the voltage. Connect the (V.A.G 1526D) to connectors - 1 and 5 - on the (VAS 5565).
- Operate the (V.A.G 1348/3A) for 30 seconds and measure the voltage.
- Compare the quantity of fuel delivered with specification.
*) Minimum delivery rate cm3/30 s
**) Voltage at FP with engine at stand still and pump running.
Example:
During test, a voltage of 10.5 Volts is measured. This results in a minimum delivery quantity of approximately 580 cm 3/30 s.
If the Specification is Not Obtained
- Check supply line to filter for possible restrictions (kinks) or clogging.
If fuel line is OK:
- Remove the cap from the fuel filler neck and repeat the test. If the fuel delivery quantity is now reached, check the fuel tank ventilation.
If Specified Value is Again Not Obtained
- Check the fuel filter as follows:
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the connection wrap a cloth around the connection. Loosen the connection carefully to release the pressure.
- Disconnect the fuel supply line - arrow - on the fuel filter.
- Connect the (VAS 6550) to the fuel supply line with the (VAS 6550/1). Hold the (VAS 6550/2) in the measuring container.
- Make sure the drain is closed and the shut off valves are open.
- Operate the (V.A.G 1348/3A). Slowly close the shut off valve - A - until the (VAS 6550) reads 4 bar. From this point on do not move position of the shut off valve.
- Empty measuring container.
- Repeat the fuel delivery test.
If the minimum delivery rate is now obtained:
- Replace fuel filter.
If minimum delivery rate is again not obtained:
- Remove the fuel delivery unit and check 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 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, intermittent loss of fuel supply):
- Check Fuel Pump (FP) current draw. Refer to => [ Current Draw, Checking ].
Current Draw, Checking
- Remove the rear seat bench.
- Remove the cover from the fuel delivery unit.
- 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.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Connect the (VAS 5565) to the connector on the cover and on the fuel delivery unit.
- Connect the current clamp - A - to the red wire -with the word "current clamp"- on the (VAS 5565).
- Start the engine and run at idle speed.
- Measure current draw of fuel pump.
• Specified value: maximum 9 amps
• The fuel pump starting current may be higher than the specified value briefly when starting the engine.
• If the malfunction in the fuel system only occurs sporadically, the test can also be performed during a road test. A second person is needed to do this.
If the current draw is exceeded:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
Fuel Pump Check Valve, Checking
- Remove the rear seat bench.
- Remove the cover from the fuel delivery unit.
- 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.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Connect the (VAS 5565) to the connector on the cover and on the fuel delivery unit.
- Connect the (V.A.G 1348/3A) to the (VAS 5565) and to the battery positive (+).
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the connection wrap a cloth around the connection. Loosen the connection carefully to release the pressure.
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) to the fuel supply line with the (VAS 6550/1). Hold the (VAS 6550/2) in the measuring container.
- Close the shut off valve - A - on the (VAS 6550) so the valve is perpendicular to the direction of flow.
- Operate remote control at short intervals, until a pressure of approximately 4 bar has built up.
CAUTION!
Danger of spraying when opening shut-off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- If pressure builds up too high, lower excess pressure by carefully opening the shut off valve.
- Watch the pressure decrease on the pressure gauge. 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:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.