Audi Workshop Service and Repair Manuals

Checking residual pressure in fuel system (up to high-pressure pump) Special tools and workshop equipment required

t  Pressure tester -VAS 6550- with hoses -VAS 6550/1- and -VAS 6550/2- t  Vehicle diagnostic tester t  Fuel-resistant measuring container Test conditions: l  Battery voltage at least 12.5 V. l  Fuel filter OK. l  Fuel tank at least 1/4 full. l  Fuel pump control unit -J538- OK. l  Ignition off. Checking fuel pressure   WARNING Risk of injury - fuel system operates under high pressure. To reduce the pressure in the fuel system, wrap a clean cloth around the connection and carefully loosen the connection.

–  Disconnect fuel line -1- by pulling release ring -2-. –  Connect pressure tester -VAS 6550- to fuel supply line with hose -VAS 6550/2-.

–  Attach hose -VAS 6550/1- and hold end of hose into fuel-resistant measuring container.   Caution Risk of fuel escaping. t  Make sure that drain tap -C- is closed. t  The lever should point perpendicular to direction of flow. –  Open cut-off valves -A- and -B-. l  Levers must point in direction of flow. –  Connect a → Vehicle diagnostic tester. –  Select „Engine electronics“ in vehicle self-diagnosis. –  Then select „Final control diagnosis“. –  Select „Fuel pump electronics“ from list and press „start“.   Note This function activates the fuel pump.

–  When fuel emerging is free of bubbles, close cut-off valve -B- to allow fuel pressure to build up. l  Lever is at right angle to direction of flow -arrow-. –  Read fuel pressure off pressure tester -VAS 6550-: l  Specification: 4.0 ... 7.0 bar –  Terminate final control diagnosis. If specification is not obtained: –  Check delivery rate of fuel pump → Rep. gr.20. Checking residual pressure –  Check system for leaks and check residual pressure by watching the drop in pressure on the pressure tester -VAS 6550-. l  After 10 minutes pressure should still be at least 3 bar. If the residual pressure drops below 3 bar: t  Check connections between pressure tester -VAS 6550- and fuel supply line for leaks. t  Check pressure tester -VAS 6550- for leaks. t  Check fuel lines and their connections for leaks. t  Renew fuel filter with integrated fuel pressure regulator → Rep. gr.20. t  Non-return valve of fuel pump is defective → Rep. gr.20. Assembly is carried out in the reverse order; note the following: –  Switch off ignition.   Note

Before removing the pressure tester, release the fuel pressure by opening the cut-off valve -B- and allowing fuel to drain off into a measuring container. –  Remove pressure tester -VAS 6550- with hoses -VAS 6550/1- and -VAS 6550/2-

–  Reconnect fuel supply line -1- (make sure that all parts are clean). –  Press fuel line in again and then pull to check that plug-in connector is correctly engaged.   Note Check fuel system for leaks.