Unscrew the fastening of the cover above the valve injectors.
Leave the engine to idle.
With the engine running, use a stethoscope to check the operation of each injector valve. The opening and closing of the nozzle valve must be clearly audible.
If the stethoscope is not present, valve actuation can be felt by touching the nozzle with a screwdriver or finger.
If the noise of the valve is absent or is uncharacteristic, then it is necessary to check the supply voltage, the winding resistance and the tightness of the valve injector.
Checking the supply voltage and resistance
Check supply voltage. To do this, remove the plugs from the valve injectors and connect a semiconductor test lamp between the two contacts of the supply cable. When turned on by the starter assistant, the control lamp should flash.
If the control lamp does not flash, the cause of the malfunction may be an open circuit or the control unit itself.
Switch off the ignition.
Connect an ohmmeter to both terminals on the injector and measure the resistance. If the winding resistance of any injector does not meet the prescribed value, it must be replaced. The prescribed resistance value is 15-17 Ω.
If necessary, replace the defective valve injector.
Leak test
Remove valve injectors. Leave the injectors and fuel lines connected to the fuel distribution manifold.
Fit the plug-in trim with electrical connectors onto the valve injectors.
Insert valve nozzles into a suitable measuring vessel.
Ask an assistant to turn on the starter for a few seconds, while comparing the shape of the nozzle jets with each other. The fuel should come out in a cone-shaped jet, the same for all nozzles.
Switch off the ignition.
Remove the plug cover from the valve injectors.
Turn on the ignition for about 5 seconds, do not turn on the starter. Check for tightness: after a minute, no more than one drop of fuel should appear on the nozzles of the valve injectors.
Install injectors.
Attention: At the workshop for BMW vehicles, the tightness of the removed valve injectors is checked with compressed air. Leaky nozzles are repaired using a cleaning fluid in a special ultrasonic unit.