Using electrical tools VW 1318 or similar pressure sensor 17 bar), connect the sensor to the system in a convenient place to measure the pressure in the fuel line. This can be done either in the fuel supply pipe or before the pressure regulator. If a special tool is used, set the lever so that the valve is open.
Disconnect the vacuum tube from the pressure regulator.
Remove the fuel pump relay from the main relay panel and connect the long wire to terminal 52. If you have the special tool US 4480/3 or similar, connect it in place of the fuel pump relay with the switch off
Apply 12V to the connected wire or turn the switch of the special device to turn on the fuel pump. The pressure should be 3.8-4.2 bar. If the pressure is low, check the amount of fuel supplied by the pump.
If fuel is leaking from the regulator where the vacuum hose connects, replace the regulator.
Install the fuel pump relay and start the engine. With the engine idling and warmed up to operating temperature, connect the vacuum hose to the pressure regulator. The pressure should drop by about 0.6 bar. If this does not happen, check to see if the return pipe is clogged, if there is no vacuum in the pressure regulator, or if the regulator is faulty.
Measuring the amount of fuel supplied
Remove the fuel pump relay from the main relay panel and connect the long wire to terminal 52. If you have the US 4 480/3 or similar tool, connect it in place of the pump relay with the switch off.
Remove the fuel pump cover from the boot floor. On some models, you may need to raise and support the vehicle securely to gain access to the pump. Pull the rubber cap off the fuel pump connector to expose the terminals, leaving the connector connected to the pump.
Using a voltmeter, connect the wires to the terminals and apply 12V to the wire or turn the switch of the special device to the on position to start the pump.
Check and record the voltage value with the pump running. It should be at least 9V. Turn off the pump.
In the engine compartment, disconnect the fuel return line connections and place them in a large container. On 4-cylinder and 10-valve 5-cylinder engines, turn on the fuel pump for 3 seconds and measure the amount of fuel collected in the container. Depending on the voltage at the pump, the amount of fuel should be approximately:
- 9 V - 335 cm³.
- 1B - 45cm³.
- 11 V - 60 cm³.
- 12V- 76cm³.
On turbocharged engines with 5 cylinders and 2 valves, turn on the pump for 15 seconds. Depending on the voltage on the pump, the amount of fuel supplied should be approximately:
- 8 V - 295 cm³.
- 9 V - 355 cm³.
- 1B - 48cm³.
- 11 V - 56 cm³.
- 12V - 66cm³.
- 13 V - 75 cm³.
- 14 V - 835 cm³.