Fuel Injection System

Before Opening High Pressure Fuel Injection System

CAUTION!
The fuel injection system is divided into a high pressure section (maximum approximately 110 bar) and a low pressure system (approximately 6 bar).

Before opening high pressure parts, e.g. removing high pressure pump, fuel rail, fuel injectors, fuel pipes, etc., reduce the fuel pressure in the high pressure area to a residual pressure of approximately 6 bar. The procedure for this is as follows.

Special tools, testers and auxiliary items required

• Vehicle diagnostic, testing, and information system (VAS 5051B)

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 35 and 45 bar

- Remove right instrument panel cover.

- Remove fuel pump control module (J538) fuse in the fuse panel with the engine idling, see.





- Check 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 the 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).

CAUTION!
Do not let fuel come into contact with skin.

• Wear protective eye-wear and clothing when opening the fuel system.

• Lay clean cloths around the connection before opening the high pressure area to collect any fuel that leaks out.

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

Final procedures

- Re-install the fuel pump control module (J538) fuse.

- Erase the DTC memory and, using "Guided Fault Finding", generate the readiness code in the engine control module Vehicle Diagnosis, Testing and Information System (VAS 5051B).