1st technique
When fuel is supplied under pressure from the injection pump to the injector, the injection pressure changes between the start of injection and the end of injection. This change in pressure is manifested in a healthy injector in the vibration of the injector needle valve. When checking the valve on a special device, a characteristic vibrating sound should be heard. Vibration testing of the needle valve is performed as follows. Clean nozzles. Connect the injector to the jig with a pressure gauge to check the injection pressure (pic. 3-45). By evenly pumping the handle of the pump of the device, create injection pressure. Open the manometer cock. When fuel runs out of the injector, a uniform vibrating sound should be heard. An uneven or no vibrating sound indicates a malfunctioning sprayer or a stuck nozzle needle valve. In this case, the nozzle must be replaced.
2nd technique
Clean nozzle. Immerse the valve needle in clean oil and push it all the way into the nozzle body, then pull it out ⅔ of the way.
Release the needle, which should fall on the saddle under its own weight.
If the needle does not drop, replace the nozzle assembly.
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