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 and workshop equipment 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.
- Remove right instrument panel cover. Refer to INSTRUMENT PANEL .
- Remove fuel pump control module -J538- fuse in the fuse panel with the engine idling, see appropriate System Wiring Diagrams information.
- 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.
Specified value: Between 35 and 45 bar
NOTE:
The fuel pressure must not drop below 6 bar, because otherwise the engine will shut off (risk of catalytic converter damage).
WARNING:
Do not let fuel come into contact with skin.
- Wear protective eyewear 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-.