Petrol engines
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.
Models 3161, 318i produced before August 1993: 4 - return fuel hose.
Models 316i, 318i from September 1993: The fuel hose is located in the appropriate place under the intake pipe. 2 = Fuel return hose.
Models 320i,325i, 328i: 6 = Fuel return hose.
Disconnect the fuel return hose from the distribution pipe and lower the hose into a measuring vessel with a capacity of approximately 2 l).
Remove the fuel pump relay. The fuel pump relay is located in the relay box on the left rear of the engine compartment.
Jumper terminals 30 and 87b (on a diesel engine terminal 87) on the relay platform 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 about 1 liter. At the same time, the fuel pump consumption is 5.5 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.
(Information taken from this resource: www.bmwman.ru)