Before Opening High Pressure Fuel Injection System

Before Opening High Pressure Fuel Injection System

The fuel injection system is divided into a high pressure section (maximum approximately 150 bar) and a low pressure system (approximately 7 bar).

Before opening high pressure parts, e.g. removing high pressure pump, fuel rail, fuel injectors, fuel pipes or Fuel Pressure Sensor (G247), fuel pressure in high pressure area must be reduced to a residual pressure of approximately 7 bar. The procedure for this is as follows.

High fuel pressure, reducing

- Connect Vehicle Diagnosis, testing & info. system (VAS 5051B).

- Start engine and run at idle speed.

- Select "engine electronics" in OBD.

- Then select "Measured values" read out.

- Select measured value block 140.

- With the engine running at idle, the fuel pressure will be displayed in display field 3.

• Specified value: Between 45 and 55 bar

- The fuse is located in the fuse holder in the right of the luggage compartment.





- With the engine running at idle, pull out - SF 6 - fuse from the fuel pump control module (J538).

• By removing fuse - SF 6 -, the voltage supply to terminal 30 for the Fuel Pump (FP) Control Module (J538) is interrupted.

- Check the fuel pressure on the tester.

• The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel from the transfer fuel pump (G6).

- Switch ignition off as soon as the fuel pressure drops to approximately 8 bar.

• The fuel pressure must not drop below 6 bar, because otherwise the engine will shut off (risk of catalytic converter damage).

The fuel lines will continue to be filled with fuel, but will no longer be under high pressure. To open fuel system, wear protective eyewear and clothing to prevent injuries and contact with skin.

Before opening the high pressure system, place a cloth around the connection.

- After reducing fuel pressure, place a clean cloth around the connection and open the high pressure system immediately. Escaping fuel must be absorbed.

Perform the following steps are completing all work:

- Install fuse.

- Erase the DTC memory and, using "Guided Fault Finding", generate the readiness code in the engine control module Vehicle Diagnosis and Service System (VAS 5052 A).