Before Opening High Pressure Fuel Injection System

Before Opening High Pressure Fuel Injection System

• The fuel injection system is separated into a high-pressure section (maximum approximately 120 bar) and a low-pressure section (approximately 6 bar).

• Before a component in the fuel injection system high pressure area is remove, the fuel pressure must be definitely reduced to a residual pressure of approximately 6 bar, as described in the following.

Special tools, testers and auxiliary items required

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

Procedure

- With the ignition off, connect the vehicle diagnosis, testing and information system (VAS 5051B) to the Data Link Connector (DLC) - arrow - using the diagnostic lead.





- Start engine and let run at idle.

Display on (VAS 5051B):





- Press the Vehicle Self-Diagnosis button - 1 - in the selection.

Display on (VAS 5051B):





- In selection - 1 -, press the "Engine electronics" vehicle system and continue by pressing the -> button.

Display on (VAS 5051B):





- In selection - 1 -, press the "Measured values" function and continue by pressing the -> button.

Display on (VAS 5051B):





- In button field - 1 -, press the 1 4 0 buttons for "Display group 140" and confirm the entry by pressing the Q button.

Display on (VAS 5051B):





- Check read-out for fuel pressure in fuel rail in display field - 3 -.

• A value of 35 to 45 bar is displayed when the engine is running at idle. The display shows the actual pressure in the fuel rail which is generated by the high pressure pump.

- Remove the right luggage compartment side trim.

- Remove the fuse 6 (on fuse panel F) (SF6) for the fuel pump control module (J538) in the fuse holder in the right of the luggage compartment.





Display on (VAS 5051B):





- With the engine still running, check the fuel pressure in fuel system display - 3 -:

• The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel by the electrical fuel pump.

- Switch the ignition off as soon as the fuel pressure drops below 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 rail will continue to be filled with fuel, but it will no longer be under high pressure.

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.

- Loosen the wire at a connection immediately.

• If the high pressure system is not opened immediately, the pressure will increase because of post-heating.

Final procedures

- Insert fuse 6 (on fuse panel F) (SF6).

- Connect the vehicle diagnosis, testing and information system (VAS 5051B) while the ignition is switched off.

- Start "Guided Functions" operating mode.

- Generate the readiness code in the engine control module.