Fuel and Residual Pressures Before High Pressure Pump, Checking

Fuel and Residual Pressures before High Pressure Pump, Checking

Special tools, testers and auxiliary items required

• Hand held remote control (jumper).

• Electrical connector test lead set.

• Fuel pressure test set (high pressure).

• Measuring container, fuel-resistant.

Test requirements

• The Fuel Pump (FP) Control Module (J538) OK.

• The fuel filter OK.

• The parking brake engaged.

• Battery voltage at least 12.5 V.

• The selector lever of automatic transmission in position "P" or " N".

• All electrical consumers switched off (radiator fan must NOT run during test).

• A/C switched off.

• The fuel tank at least 1/4 filled.

• The ignition switched off.

Checking system pressure

- Remove the rear seat bench.

- Remove the cover for the right locking flange - arrows -.





- Disconnect the electrical harness connector - arrow - from the fuel delivery unit.





- Connect a Hand held remote control (jumper) to terminal - 1 - of the fuel delivery unit and to vehicle battery (+).

- Connect a jumper cable from a Electrical connector test lead set to terminal - 5 - of the fuel delivery unit and to vehicle Ground (GND).





- Remove the rear engine cover - arrows -.





CAUTION!
The fuel system is under high pressure! Before opening high pressure components of the fuel injection system, pressure must be relieved to residual pressure. Then wrap a clean rag around the connection and relieve residual pressure by carefully loosening the connection.

- Disconnect the fuel line - arrow -.





- Connect the Fuel pressure test set (high pressure) to the fuel line.

- Connect the assisting hose - arrow - to the pressure gauge and hold in the measuring container.





- Open the pressure gauge shut-off valve. The lever points in direction of flow.

- Press the switch on the Hand held remote control (jumper) briefly to bleed the fuel system

- Close the pressure gauge shut-off valve. The lever is perpendicular to the direction of flow - arrow -.





- Press the switch on the Hand held remote control (jumper) until no more pressure increase is observed on the fuel pressure gauge.

• Specification: approx. 6 bar positive pressure

If the specification was not obtained:

- Check the delivery rate of the fuel pump. Refer to => [ Fuel Pump Delivery Quantity, Checking ] Fuel Pump Delivery Quantity, Checking.

Checking residual pressure

- Check for leaks and residual pressure by observing the pressure loss on the pressure gauge.

• After 10 minutes there must be a residual pressure of at least 3.75 bar.

The holding pressure drops below 3.75 bar:

• Check the connection between the fuel pressure gauge and the fuel line for leaks.

• Check the pressure gauge for leaks.

• Check the fuel lines and their connections for leaks.

• Replace the fuel filter with integrated fuel pressure regulator.

• Replace the fuel pump.

Assembly is performed in the reverse order of removal. Note the following:

• Before disconnecting the pressure gauge, release the fuel pressure by opening the shut-off valve. Hold a container under the connection.

Torque specifications