Unscrew the bolts and remove the cover over the nozzle.
The engine must be running at idle.
Using a stethoscope, check each injector with the engine running to see if there are any clicks during operation. These clicks correspond to the moments of opening and closing of the nozzle.
If there is no stethoscope, then you can check the operation of the nozzle by attaching a screwdriver or even a finger to it.
If there is no noise from the operation of the nozzles or they are somehow unusual, then you need to check the voltage supply, resistance and density of the nozzles.
Checking the voltage supply and resistance
Check voltage supply. To do this, remove the nozzles and connect the control pump (Light-emitting diode) between the pins of the plug. The assistant should turn on the starter, and the LED should flash.
If the LED does not blink, then the fault may be in the wires or in the control unit itself.
Switch off the ignition.
Connect an ohmmeter to the terminals of each injector and measure the resistance. If the resistance of one or more injectors differs from the required (15 -17.5 ohm), then her (their) need to replace.
Replace nozzle if necessary.
Density test
Remove nozzles. Valves and fuel lines remain connected on the distribution pipe.
Make electrical connections (bar) on the injectors.
Lower the nozzles into suitable measuring containers.
Have an assistant turn on the starter for a few seconds. During its operation, compare the shape of the fuel jet from different nozzles. It should be approximately the same for all nozzles and have the form of a cone.
Switch off the ignition.
Remove the electrical connections from the injectors.
Turn on the ignition for about 5 seconds without turning on the starter, then check the density: no more than one drop of fuel should come out of the injectors in 1 minute.
Install injectors.
Attention: In specialized workshops, the tightness of the removed nozzles is checked using compressed air. Loose nozzles are cleaned in a special ultrasonic device using a special cleaning fluid.