Note: On diesel engines, the fuel pressure is measured in the fuel line between the filter and the high-pressure fuel pump, which can only be done at a service station.
The condition for testing is a normally charged battery.
Disconnect the fuel supply hose 3 from the distribution pipe (on a diesel engine - from the high-pressure fuel pump) and lower the hose into a measuring vessel with a capacity of about 5 l).
Remove the fuel pump relay. The fuel pump relay is located in the relay box on the right rear of the engine compartment. The fuel pump relay is brown on 520i/525i/524td models and orange on 530t/535i models.
Short-circuit terminals 30 and 87 on the relay pad with a short jumper with a diameter of 1.5 mm and start the fuel pump for about 30 seconds.
In 30 seconds, the amount of fuel supplied should be 875 cm³. At the same time, the fuel pump consumption is 5 amperes.
If less fuel is supplied, replace the fuel filter and check the pump performance again. If the performance is still insufficient, replace the fuel pump.