Audi Workshop Service and Repair Manuals

Checking return flow rate of injectors with engine running   Note Checking return flow rate if engine does not start → Chapter Special tools and workshop equipment required

t  Hose clamps for hoses up to 25 mm -3094-

t  Injector rate comparison meter -V.A.G 1348/2B- for measuring return flow rate of each injector t  Fuel-resistant measuring container t  3 test hoses (made up in the workshop) to fit return line connections on injectors Measuring return flow rate of all injectors

–  Pull off engine cover panel → Chapter. –  Clamp off fuel return hose -arrow- downstream of restrictor -1- using hose clamp up to 25 mm -3094- and disconnect fuel return hose.   Caution Risk of malfunctions caused by dirt. Observe → Chapter „Safety precautions when working on the fuel system“.

–  Connect test hose -1- to restrictor -2- and hold end of hose in measuring container. –  Start engine and run at idling speed for two minutes: t  Return flow rate after 2 minutes: 30 ... 55 ml –  If specification is attained, increase engine speed to 2000 ... 2500 rpm for approx. two minutes: l  Return flow rate after 2 minutes: less than 250 ml If specification is exceeded, this indicates that one or more injectors are defective. You must then check the return flow rate from each injector individually. Measuring return flow rate of individual injectors Each injector normally has a relatively low return flow rate. If the return flow rate at one injector is relatively high compared to the other injectors, that injector is probably defective. –  Clean all return line connections with engine cleaner or brake cleaner and dry.

–  Clamp off fuel return hose -arrow A- on cylinder bank 1 (right-side) using hose clamp up to 25 mm -3094-.   Note Disregard -arrow B-.

Caution Risk of malfunctions caused by dirt. Observe → Chapter „Safety precautions when working on the fuel system“. –  Disconnect fuel return hoses from injectors; to do so, press down both tabs and at the same time pull centre piece up to release connection -arrow-.

–  Connect test hoses onto return line connections of all three injectors and guide into meter -V.A.G 1348/2 B-. –  Start engine and run at idling speed for several minutes:   Caution Risk of damage to injectors due to increased engine speed. Do NOT press the accelerator during this test; the engine must only run at idling speed. –  When the engine is warm and running at idling speed, the return flow rates at each of the 3 injectors must not differ by more than a small amount.

–  Clamp off fuel return hose on cylinder bank 1 (right-side) upstream of restrictor using hose clamp up to 25 mm -3094--arrow B-.   Note Disregard -arrow A-. –  Repeat measurement of return flow rate for cylinder bank 2. –  If one injector has a significantly higher return flow rate than the others, it must be renewed → Chapter. Assembling Installing fuel return lines –  Renew O-rings for all return line connections.   Note Lubricate all O-rings with engine oil or assembly oil before installing. –  Push the return line connections carefully over the new seals and onto the injectors. The catch should engage audibly. Then press release pin down carefully. Bleeding fuel system and checking for leaks –  Run engine at idling speed for several minutes (do not press accelerator) and then switch off. Fuel system will bleed itself automatically. –  Check the entire fuel system for leaks. Renew the affected component if leakage occurs. –  After completing the repair, road-test the vehicle. Accelerate with full throttle at least once. Then check the high-pressure section of the fuel system again for leaks.   Note If there is any air left in the fuel system, the engine may switch to the backup mode ('emergency running' mode) during the road test. Switch off the engine and erase the event memory. Then continue the road test.