Gasoline engines
A condition for the accuracy of the test is a properly charged battery.
Remove the fuel return hose (2) from the distribution pipeline, for which loosen the clamp.
Attention: The fuel system is under pressure. Collect leaked fuel with a rag. Clamps must be replaced after loosening.
Attention: On some models, the fuel supply line is screwed directly into the distribution pipe. In this case, the O-ring must always be replaced during installation and lubricated with petroleum jelly. In another design, the fuel hose is fastened with clips, and a special tool is needed to release them. Before installation, check the O-ring and replace it if necessary.
Lower the fuel return line from the expansion pipe into a measuring vessel with a capacity of about 2 liters.
Pull out the fuel pump relay. The relay is located in the relay box at the rear left in the engine compartment.
In the relay socket, bridge terminals 30 and 87 with a 1.5 mm auxiliary wire and let the fuel pump run for about 30 seconds.
In 30 seconds, the pump should supply about 1 liter of fuel. During operation, the current consumed by the pump is about 9.5 A.
If too little fuel is supplied, replace the fuel filter and check performance again. If it is still low, replace the fuel pump.