Fuel Pump, Check
Fuel Pump, Checking
Special tools, workshop equipment, test and measuring appliances and aux. items required
- 3217 Union nut spanner
- V.A.G 1318 Pressure tester
- V.A.G 1318/1 Adapter
- V.A.G 1318/11 Adapter
- V.A.G 1318/17 Adapter
- V.A.G 1318/23 Adapter
- V.A.G 1332 Torque wrench (40 to 200 Nm)
- V.A.G 1348 Fuel quantity comparison meter
- V.A.G 1466 Test system
- VAG 1527 B voltage tester
- V.A.G 1594 A Adapter set
- V.A.G 1715 Multimeter
- Measuring container
- Wiring diagram
Check conditions
- Fuse No. 28 OK.
- The battery voltage must be at least 11.5 V.
- All electrical consumers, e.g. lights and rear window heating must be switched off.
- If the vehicle is equipped with an air conditioner, this must be switched off.
NOTE: Observe description of function of crash fuel shut-off.
Checking function and voltage supply
NOTE: Check whether a coded radio is installed as during the forthcoming work sequences the battery Ground strap must be disconnected. Obtain radio code first if necessary.
- Remove cover from fuel delivery unit.
- Briefly operate starter. Fuel pump must be heard to run.
- Switch off ignition.
If the fuel pump does not run:
- Remove cover in front of fuse holder.
- Pull fuse No. 28 out of fuse holder.
- Connect remote control V.A.G 1348/3A with adapter cable V.A.G 1348/3-2 to contact 28a to fuel pump and battery positive (+).
- Operate remote control.
Fuel pump runs:
- Check activation of fuel pump relay using wiring diagram and V.A.G 1466 A:
Fuel pump does not run:
- Pull 4 pin connector off flange on fuel delivery unit.
- Connect VAG 1527 B voltage tester with aux. cables from V.A.G 1594 A to the outer contacts of the connector.
- Operate remote control. LED must light up
LED does not light up:
- Locate and eliminate open circuit using wiring diagram:
LED lights up (voltage supply OK.):
- Remove union nut with spanner 3217.
- Check that the electrical wires between flange and fuel pump are connected.
If no open circuit can be found:
- Fuel pump malfunctioning, replace fuel delivery unit.
Checking delivery rate
Check conditions
- Voltage supply OK.
- Remote control V.A.G 1348/3A connected.
Test sequence
- Remove filler cap from fuel tank filler neck.
WARNING!
Fuel system is underpressure! Before opening the system place a cloth around the connection. Then release pressure by carefully loosening the connection.
- Pull off supply pipe/hose -1 - and collect leaking fuel with a cloth.
- Connect pressure gauge V.A.G 1318 with adapter 1318/23 and V.A.G 1318/17 to the fuel supply pipe.
- Push the hose V.A.G 1318/1 onto the adapter V.A.G 1318/11 on the pressure gauge and hold hose in a measuring container.
- Open the pressure gauge shut-off tap. The lever then points in the flow direction -A-.
- Operate remote control V.A.G 1348/3A and slowly close cut-off tap, until pressure gauge shows 3 bar. From this point on do not move position of cut-off tap.
- Empty measuring container.
- The quantity of fuel delivered by the fuel pump is dependent upon battery voltage. Therefore connect the multimeter with adapter cables from V.A.G 1594 A to the vehicle battery.
- Operate remote control for 30 seconds and measure battery voltage
- Compare the quantity of fuel delivered with specification.
*) Minimum delivery cubic cm/30 seconds
**) Voltage at fuel pump with engine stationary and pump running (approx. 2 volts less than battery voltage).
Example:
During the test a voltage of 12.5 volts is measured at the battery. As the voltage at the pump is approx. 2 volts less than the battery voltage then this will equate to a minimum delivery of 200 cubic cm/30 s.
If the minimum delivery rate is not attained:
- Check the fuel pipes for possible restrictions (kinks) or blockages.
- Pull supply hose -1- off inlet to fuel filter.
- Connect pressure gauge V.A.G 1318 with adapter 1318/17 to fuel supply pipe.
- Repeat delivery rate check.
If the minimum delivery rate is now attained:
- Replace the fuel filter.
If the minimum delivery rate is again not attained:
- Remove the fuel delivery unit and check the strainer filter for soiling.
Only when up to now no fault has been detected:
- Fuel pump malfunctioning, replace fuel delivery unit.
- Check DTC memory:
- Read out readiness code:
- If the DTC memory has been erased or the engine control module separated from the permanent positive, the readiness code must be generated again.
If the delivery rate has been attained but nevertheless you suspect a fuel supply system fault (e.g. intermittent failure of fuel supply system):
- Check the current draw of the fuel pump as follows:
- Reconnect all disconnected fuel pipes.
- Connect multimeter V.A.G 1715 to wire -arrow- for contact 1 of 4-pin connector using the pick-up clamp.
- Start the engine and run at idling speed.
- Measure the current draw of the fuel pump. Specification: max. 8 amps.
NOTE: If the fuel system malfunction is intermittent, you can perform the check during a test drive with the help of a 2nd person.
If the current draw is exceeded:
- Fuel pump malfunctioning, replace fuel delivery unit.
- Check DTC memory:
- Read out readiness code:
- If the DTC memory has been erased or the engine control module separated from the permanent positive, the readiness code must be generated again.
Checking fuel pump non-return valve
Test conditions
- Remote control V.A.G 1348/3A is still connected.
- Pressure gauge V.A.G 1318 is still connected.
Test sequence
NOTE: With this check the fuel supply pipe connections from the fuel delivery unit to the point at which the pressure gauge V.A.G 1318 is connected will be checked for leaks at the same time.
- Close pressure gauge shut-off tap (lever at right angles to through flow direction -position -B-).
- Separate remote control at short intervals, until a pressure of Approx. 3 bar has built up.
WARNING!
Danger of spray when opening the shut-off tap, hold container over the pressure gauge free connection.
- If pressure builds up too high, lower excess pressure by carefully opening the shut-off tap.
- Watch pressure drop on gauge. After 10 minutes the pressure must not drop below 2.5 bar.
If the pressure drops further:
- Check pipe connections for leaks.
If no fault is detected in the wiring:
- Fuel pump malfunctioning, replace fuel delivery unit.
- Check DTC memory:
- Read out readiness code:
- If the DTC memory has been erased or the engine control module separated from the permanent positive, the readiness code must be generated again.