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Fuel delivery quantity: check > < Checking fuel pressure

Leon Mk2

Retention pressure: check
Retention pressure: check
   
l  Fuel pressure is correct and the pressure gauge -VAS 6550- connected. Check the fuel pressure → Chapter.
Checking sequence
–  Actuate fuel pump with final control diagnosis to build up fuel pressure.
–  Read the fuel pressure on the pressure gauge.
l  Specification: 4.0 - 7.0 bar
–  Observe pressure drop on the pressure tester. After 10 minutes the pressure must not drop below 3.0 bar.
If the pressure drops further:
–  Actuate fuel pump with final control diagnosis to build up fuel pressure.
  N20-10628
–  After pressure has been built up, immediately close the shut-off valve -B- on the pressure gauge. 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 the fuel pipe leading to fuel filter for leaks.
If no fault in fuel piping is detected:
–  Check the non-return valve in the fuel return line. Proceed as follows:
  N20-10598
–  Pull fuel supply line -arrow- off fuel filter.
  N20-10629
–  Connect pressure tester -VAS 6550- between fuel filter and fuel supply line with adapter -VAS 6550/1- and -VAS 6550/2-.
–  Make sure that drain tap is closed and cut-off taps are open.
–  Actuate fuel pump with final control diagnosis to build up fuel pressure.
–  Read the fuel pressure 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 the pressure tester. 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