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Injection system > < Rules for cleanliness

A3 Mk2

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. 150 bar) and a low-pressure section (approx. 7 bar).
Prior to opening the high-pressure section (e.g. when removing the high-pressure pump, fuel rail, injectors, fuel pipes or fuel pressure sender -G247-), the fuel pressure in the high-pressure section must be reduced to a residual pressure of approx. 7 bar. 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 function read “Measured values”.
–  Select measured value block 140.
–  With engine idling the fuel pressure is displayed in zone 3.
t  Specification: between 35 and 45 bar
   
–  Pry off cover on left side of dash panel using front-end hook -3370--arrow-.
  A97-0808
–  With engine idling, pull out fuse -SC 27- for fuel pump control unit -J538- in fuse holder in dash panel (driver's side).
–  Observe fuel pressure displayed on tester.
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-.
  A97-0972

Injection system > < Rules for cleanliness