Holding Pressure, Checking: Notes
Special tools and workshop equipment required
- Pressure Tester Kit VAS6550
- Trim Removal Wedge 3409
- Vehicle Diagnostic Tester
The coupling must audibly engage when locking.
Note the color coding when installing the coupling, refer to Coupling Allocation !
Pull on the coupling to make sure it is secure.
Disconnecting the coupling, refer to COUPLING, DISCONNECTING .
Conditions
- The fuel pressure is OK and the Pressure Tester Kit VAS6550 is still connected. Checking the fuel pressure, refer to FUEL PRESSURE, CHECKING .
Test Sequence
-- Activate the fuel pump with output diagnostic test mode to build fuel pressure.
-- Read the fuel pressure.
- Specified value: 4.0 to 7.0 bar (58 to 102 psi)
-- Observe the pressure drop on the pressure tester. After 10 minutes the pressure must not drop below a 1.0 bar (15 psi) decrease.
If the pressure drops further:
-- Activate the fuel pump with output diagnostic test mode to build fuel pressure.
-- Make sure the drain valve -C- is closed and the shut-off valves -A- and -B- on the Pressure Tester Kit VAS6550 -1- are open.
-- Close the shut off lever -B- on the pressure tester immediately after the pressure has been reached. The lever is perpendicular to the direction of flow.
If the pressure drops again (leaks in the fuel tank):
Check for the leak on the fuel tank side. Proceed as follows:
-- Check the fuel lines inside the engine compartment for leaks, refer to Fuel Pressure Sensor -G247-, CHECKING .
If not faults can be determined, check the holding pressure on the delivery unit flange, refer to Check the residual pressure at the fuel delivery unit flange .
-- Proceed as follows.
If the pressure no longer drops now (leaks on the engine side):
Look for leaks on the engine side. Repeat the pressure holding test. Close the shut off lever -A- this time to determine if there actually is a leak on the engine side.
-- Repeat the holding pressure test while at the same time closing the shut-off valve -A-.
-- If there is a leak on the engine side, then check the fuel pipes and the high-pressure pump for leaks, refer to Fuel Pressure Sensor -G247-, CHECKING .
If no faults can be found, check the fuel injectors for leaks:
-- Remove the spark plugs, refer to OVERVIEW - IGNITION SYSTEM .
-- Open the drains -A- and -B-.
-- Start the fuel pump using output diagnostic test mode .
-- Look into the spark plug shaft and see if any fuel has gathered at the bottom caused by a leaky fuel injector.