Procedure That Must Be Performed Before Opening the High-Pressure Fuel Injection System

Procedure That Must Be Performed Before Opening The High-pressure Fuel Injection System - Pay Close Attention

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

Before opening high-pressure section - e.g. removing high-pressure pump, fuel rail, fuel injectors, the motor for intake manifold runner control valve or any other component or fuel line that is located in high-pressure section of the fuel injection system - the fuel pressure in high-pressure section must be relieved to a residual pressure of approx. 8 bar. The procedure for this is as follows.







- Disconnect electrical harness connector from Evaporative Emission (EVAP) Canister Purge Regulator Valve N80 -1-.

NOTE: The engine control module (ECM) is selected with the vehicle diagnostic, testing and information system VAS5051, then the display group 140 is selected under function "Read measuring value block".







- Connect vehicle diagnosis, testing and information system VAS5051 with diagnostic cable VAS5051/1.







- Display on VAS5051:
- Press button "On-Board Diagnostics".







Display on VAS5051:
- In selection -1-, press vehicle system "01 - Engine electronics".







Display on VAS5051:
1. Selection of diagnostic functions:

- In selection -1-, click on diagnostic function "08 - Read measuring value block".







Display on VAS5051:
- In button field -2-, select display group 140 and confirm input by pressing Q button.







Display on VAS5051:
1. Display group X
2. Display field 1

- Display field 2
- Display field 3
- Display field 4

- Start engine and run at idle speed.

Observe the indication in display field 3. With engine at idle, a value of approx. 49 bar is indicated in display field 3. The indication shows actual pressure (current pressure) in fuel rail, produced by high-pressure pump.







- Remove fuse no. 28 for Fuel Pump (FP) Control Module J538 and continue observing indication in display field 3. The engine must run at idle.

The indication in display field 3 will drop very quickly after 1 to 2 minutes, because the mechanical high-pressure pump is no longer supplied with fuel from the electrical fuel pump from fuel tank.

NOTE: The indication must not drop below 6 bar, because otherwise the engine will shut off (risk of catalytic converter
damage).

- Switch ignition off, once an indication of approx. 8 bar is achieved.

The fuel rail will continue to be filled with fuel, but it will no longer be under high pressure.

Now, components or lines can be opened. A clean rag is to be placed around the connection. Catch the escaping fuel.
- Install fuse for Fuel Pump (FP) Control Module J538 again.
- After the repair, check DTC memory of engine control module (ECM) and erase it.
- In operating mode "Guided Fault-finding", generate readiness code for engine control module (ECM).