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A 2010 km Jiangling X8 vehicle with a mileage of about 75 thousand km and equipped with R425DOHC electronically controlled high pressure common rail diesel engine. Users reflect: the engine in the shutdown 60min or when the temperature is low, its starting performance is poor, the starting machine needs to continue to run over 4S to catch fire, and sometimes it is necessary to start a lot of success. After receiving the car: in accordance with the principle of "easy to get ahead", "difficult to go outside", "first out of the machine" and "electronics after the machine", the car will be investigated after parking for a night. The connection of the components of the engine fuel system, the connection of the wiring harness connectors and harness of the electronic control system, and the preheating system of the engine have not been found. Then the engine is started, the ignition switch is rotated from "OFF" bit to "ON" position, the engine fault light on the combined instrument is lit and then extinguished, indicating that the engine electronic control system is self checking without fault. Then turn the ignition switch to the "START" gear. The starter works well, and the engine has symptoms, but it can't start the machine. Then it started 3 times continuously, and the engine finally started successfully. When the engine temperature is normal, then it will be extinguished. The engine will start smoothly after stopping 10min. The road test on the vehicle made the engine run smoothly at idle speed and high speed, and its dynamic performance was good, and there was no abnormal phenomenon. This indicates that the engine is difficult to start after long time parking, and the rest are normal, which basically eliminates the possibility of failure of the mechanical part and the electric control system. Considering that the car has an omen when starting, and once everything is normal after starting the machine, it can be confirmed that the high pressure common rail part of the fuel system should also have no problem, so the fault area is locked in the low pressure oil path. First check the fuel tank and fuel line, and found no blockage or leakage. After asking the driver to know that the vehicle is not maintained in time, the fuel filter has not been replaced for a long time, so the fuel filter is replaced, and the engine can start the engine smoothly after the oil pump is discharged with the hand oil pump. But when the engine was started on the morning of the second day, the difficulty of starting the engine still existed, which indicated that there was still a problem in the low pressure oil circuit. Then the low pressure oil between the fuel tank and the oil pump was carefully checked. When the fuel filter was checked and the fuel heater wire harness connector was pulled out, a small amount of oil was found in the fuel heater wire harness connector. In order to verify, the author uses the oil pump to pump oil several times, and then observed that the fuel heater wire harness connector has oil spillover at the root. So far, the cause of engine starting difficulty has been found. Troubleshooting: replace the fuel filter assembly with oil-water separator after trial run, troubleshooting. Failure summary: the main cause of the vehicle fault is air entering low pressure oil circuit. The reason is simple, but the fault location is not easy to find. Because the crack in the wire harness connector of the fuel heater is fine, and the oil pump to the low pressure pipeline between the fuel tank is negative pressure. Even if there is air entering, there is no oil leaking trace in the wire harness connector without the oil pump oil. After the engine starts running, a small amount of air that permeated into the oil path can also be discharged through the injector, which has little effect on the operation of the engine. However, when the vehicle reaches a certain amount after a long time parking, the air entering the low-pressure oil way will affect the smooth start of the engine. At this point, it is necessary to start continuously for several times. After the air in the oil path is discharged, the system pressure of the high pressure common rail tube is formed, and the engine can start the machine.