The maintenance technicians tested the injectors and found that the atomization effect of the 0R-0471 injectors was very poor, and the fuel was sprayed in the form of oil droplets instead of a uniform cone, resulting in insufficient combustion and black smoke emission. After disassembling the injectors, it was found that the nozzle holes were worn and the internal pressure regulating spring was aging, which led to the decrease of injection pressure and poor atomization effect. In addition, the long-term use of the injectors without regular maintenance also accelerated the wear of the nozzle holes.