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Fuel delivery quantity: check > < Checking fuel pressure

Leon Mk2

Checking residual pressure
Checking residual pressure
   
l  Fuel pressure is correct and the pressure gauge -VAS 6550- connected. Fuel pressure: check → Chapter.
Checking process:
–  Control and build up the pressure of the fuel pump using the actuator diagnostic function.
–  Take the fuel pressure reading on the pressure gauge.
l  Specification: 4.0 - 7.0 bar
–  Observe pressure drop on gauge. After 10 minutes the pressure must not drop below 3.0 bar.
If the pressure drops further:
–  Control and build up the pressure of the fuel pump using the actuator diagnostic function.
  N20-10628
–  After reaching the desired pressure, the stop cock -B- on the pressure gauge must be closed. The lever must point horizontally in the flow direction.
If the pressure does not drop any more,
  Note
Search for the leak on the engine side. Repeat the pressure retention test. This time, close the shut-off cock -A- to check if there is actually a leak on the engine side.
–  Check fuel pipe leading to high-pressure pump for leaks.
If no fault is found:
–  Replace the high-pressure pump → Chapter.
If the pressure drops again:
The leak must be detected from the side of the fuel tank. Proceed as follows:
–  Check fuel pipe leading to the fuel filter for leaks.
If no fault in fuel piping is detected:
–  Check the non-return valve of the fuel delivery unit. Proceed as follows:
  N20-10598
–  Separate the fuel supply hose -arrow- from the fuel filter.
  N20-10629
–  Connect fuel supply line pressure gauge -VAS 6550- using the adapter -VAS 6550/1- and -VAS 6550/2- between the fuel filter and the fuel supply line.
–  Make sure that the drain cock is closed and that the flow valves are open.
–  Control and build up the pressure of the fuel pump using the actuator diagnostic function.
–  Take the fuel pressure reading on the pressure gauge.
l  Specification: 4.0 - 7.0 bar
  N20-10630
–  After pressure has been built up, close the shut-off cock -A-.
–  Observe pressure drop on gauge. After 10 minutes the pressure must not drop below 3.0 bar.
If the pressure drops:
–  Fuel pump non-return valve is faulty, replace the fuel supply unit → Chapter.
If the pressure does not drop:
–  The pressure retention valve on the fuel pump is okay. Pressure limiting valve in the fuel filter faulty: Replace the fuel filter.
  N20-10598

Fuel delivery quantity: check > < Checking fuel pressure