Volkswagen Workshop Service and Repair Manuals

Checking fuel delivery rate   Note When driving characteristic problems occur when the fuel tank is a approx. 1/4 filled, then check fuel delivery rates with approx. 1/4 filled tank or less.

–  Remove cover -1- with fuel pump control unit -J538--2- from fuel delivery unit.

–  First check that connector -1- is seated securely by pulling connector without pressing catch. The connector can cause a fault if it has not been fitted correctly. –  Now pull off connector. –  Check the contacts on the connector and on the fuel delivery unit for damage.

–  Connect test instrument adapter/DSO (5-pin) -VAS 5565- to connector and fuel delivery unit. –  Connect remote control -V.A.G 1348/3A- to adapter -VAS 5565- and to battery positive terminal in engine compartment.   Note This step serves only to have the fuel pump running when the engine is stopped.   WARNING Fuel supply line is pressurised. Wear eye protection and protective clothing to avoid possible injury and skin contact. Before loosening hose connections, wrap a cloth around the connection. Then release pressure by carefully pulling hose off connection.

–  Pull off supply line (metal coupling) -arrow- and catch escaping fuel with a cloth. Detach push-on connectors → Chapter

–  Connect pressure tester -VAS 6550- to fuel supply line with adapter -VAS 6550/2-. Hold adapter -VAS 6550/1- in a measuring container. –  Make sure that drain tap is closed and cut-off taps are open.   WARNING Danger of spraying! Wear eye protection and protective clothing to avoid possible injury and skin contact. Hold container before free connection of pressure tester. –  Press remote control -V.A.G 1348/3A-. Then slowly close shut-off tap -arrow- until a pressure of 4 bar is displayed on pressure gauge. From this point on do not move position of shut-off tap. –  Drain measuring container.

–  The quantity of fuel delivered by the fuel pump is dependant on the battery voltage, therefore, also connect multimeter -V.A.G 1715- to contacts -1 and 5- of 5-pin test instrument/DSO adapter -VAS 5565-. –  Operate remote control for 60 seconds while measuring voltage at fuel pump.

–  Compare quantity of fuel delivered with specification. *) Minimum delivery rate cm3/60 s **) Voltage at fuel pump with engine not running and pump running. Example: During the test a voltage of 10.5 volts is measured. This equates to a minimum delivery rate of approx. 1200 cm3/60 s. If the specification is not attained: –  Check fuel lines for possible restrictions (kinks) or blockages. If no fault is found: –  Remove cap from fuel filler neck and repeat check. If fuel delivery rate is now reached, check fuel tank breather. If the specifications are still not attained: –  Check fuel filter (proceed as follows):   WARNING Fuel supply line is pressurised. Wear eye protection and protective clothing to avoid possible injury and skin contact. Before loosening hose connections, wrap a cloth around the connection. Then release pressure by carefully pulling hose off connection.

–  Pull fuel supply line -arrow- off fuel filter. Detach push-on connectors → Chapter

–  Connect pressure tester -VAS 6550- to fuel supply line with adapter -VAS 6550/1-. Hold adapter -VAS 6550/2- in a measuring container. –  Make sure that drain tap is closed and cut-off taps are open. –  Press remote control -V.A.G 1348/3A-. Then slowly close shut-off tap -arrow- until a pressure of 4 bar is displayed on pressure gauge. From this point on do not move position of shut-off tap. –  Drain measuring container. –  Repeat delivery rate check. If the minimum delivery rate is now attained: –  Renew fuel filter. If the minimum delivery rate is again not attained –  Remove fuel delivery unit and check filter strainer for soiling. Only if still no fault has been detected: –  Renew fuel delivery unit. If fuel delivery rate has been attained, but nevertheless you suspect a fuel supply system fault (e.g. intermittent failure of fuel supply system): –  Measure current draw of fuel pump → Chapter.