The maintenance technicians used CATET diagnostic software to read the engine data and found that the injection timing of the 0R-3002 injectors deviated by 0.8ms from the standard value, which led to insufficient fuel combustion and uneven power output of the engine, thus causing vibration and black smoke. The root cause of the problem is that the injector was not calibrated in time after being disassembled and maintained last time, and the ECU could not accurately control the injection timing. In addition, the wear of the injector's internal needle valve also affected the stability of the injection timing.