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Ignition system, glow plug system > < Injection system

A5

Important: Required procedure prior to opening high-pressure injection system
Important: Required procedure prior to opening high-pressure injection system
  Caution
The injection system consists of a high-pressure section (maximum approx. 120 bar) and a low-pressure section (approx. 6 bar).
Prior to opening the high-pressure section (e.g. when removing the high-pressure pump, fuel rail, injectors, fuel pipes, etc.) the fuel pressure in the high-pressure section must be reduced. The procedure is described below.
Reducing fuel pressure in high-pressure section
   
–  Connect up the vehicle diagnostic, testing and information system -VAS 5051B-.
–  Start engine and run at idling speed.
–  Select “Engine electronics” in vehicle self-diagnosis.
–  Then select “Measured values”.
–  Select “Fuel pressure” from the list.
–  With the engine idling, the fuel pressure displayed will be between 30 and 40 bar.
  A00-10303
–  Pry off cover -1--arrow- on left side of dash panel using removal wedge -3409- or similar.
  A70-10665
–  With engine idling, pull out fuse for fuel pump control unit -J538- in fuse carrier in dash panel (driver's side), see → Current flow diagrams, Electrical fault finding and Fitting locations.
–  Observe fuel pressure.
l  The fuel pressure will decrease very quickly because the mechanical high-pressure pump is no longer being supplied with fuel by the fuel system pressurisation pump -G6-.
–  Switch off ignition as soon as fuel pressure has dropped to approx. 8 bar.
  Note
Fuel pressure must not fall below 6 bar, otherwise the engine will stall (this could damage the catalytic converter).
  WARNING
The fuel lines are still filled with fuel, however the fuel is no longer under high pressure. Wear safety goggles and protective clothing when opening the fuel system to avoid possible injury and skin contact.
Before opening the high-pressure section, wrap a cloth around the connection.
–  The high-pressure system must be opened “immediately” after reducing the fuel pressure; wrap a clean cloth around the connection. Catch the escaping fuel.
The following operations must be performed after completing repair work:
–  Refit fuse.
–  Erase fault memory and generate readiness code in engine control unit using “Guided Functions” mode of vehicle diagnostic, testing and information system -VAS 5051B-.
  A97-10558

Ignition system, glow plug system > < Injection system