Fuel Delivery, Checking
Fuel Pump, Checking
• When replacing the fuel delivery unit, check the fuel tank for visible contamination and clean if necessary.
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)
• Measuring Container, 2 Liter
Fuel Delivery, Checking
- Remove the rear seat bench.
- Remove the cover - 1 - with the fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First gently pull on the connector - A - without pressing the retainer to make sure it is securely connected. 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.
- Install the (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the (V.A.G 1348/3A) to the (VAS 5565) and to the battery positive terminal.
• This step allows the fuel pump to run when the engine is not running.
CAUTION!
The fuel system is under pressure!
• Wear protective goggles and protective clothing to prevent injuries and contact with skin.
• Before disconnecting the connections, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the supply line (metal coupling) - arrow - and collect any leaking fuel in a cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/2). Hold the other end of the (VAS 6550/1) in a measuring container.
- Make sure the drain is closed and the shut off valves are open.
CAUTION!
Danger of spraying when opening the 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.
- Operate the (V.A.G 1348/3A). Slowly close the shut off valve - arrow - until the (VAS 6550)shows 4 bar. From this point on do not move the position of the shut off valve.
- Empty the measuring container.
- Fuel delivery rate of the fuel pump is dependent on battery voltage. So, connect the (V.A.G 1715) to wires - 1 and 5 - of the (VAS 5565).
- Operate the (V.A.G 1348/3A) for 30 seconds and simultaneously measure the voltage at the fuel pump.
- Compare the quantity of fuel delivered with specification.
*) Minimum delivery rate cm3/30 s
**) Voltage at 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 580 cm3/30 s.
If the Specification is Not Obtained
- Check the fuel line for possible restrictions (kinks) or clogging.
If no malfunction can be found:
- 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 the Specification is Again not Obtained
- Remove the fuel delivery unit and check fuel strainer for contamination.
- If there is no malfunction here as well, replace the flange with fuel filter. Refer to - item 20 -=> [ Flange with Fuel Filter ] Fuel Tank and Components Overview
- Repeat the test.
If the specification is Again Not Obtained
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply (for example, intermittent loss of fuel supply):
- Check the fuel pump current draw. Refer to => [ Current Draw, Checking ]. Current Draw, Checking