Fuel Pressure and Residual Pressure Before High Pressure Pump , Checking

Fuel Pressure And Residual Pressure 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. Fuel Pump (FP) 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:

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

Torque specifications
Fuel line to fuel rail : 22 Nm