The mileage is about 680 thousand km, which is equipped with the Suzhou dragon YC6L330-30 KLQ6125B 1A passenger car of Guangxi Yuchai engine. The driver reflected that when the vehicle was less fuel (about 100L), the driving process had a sense of pause, as if the engine was not enough fuel, the engine failed to light, and the engine was restarted and the engine fault lights were extinguished, but the vehicle was soon reproduced and the vehicle could not speed up at this time. The engine speed is not more than 1700 r/min, and the output power of the engine is insufficient. Fault diagnosis: the maintenance technicians check the car, find the engine fault light, use the vehicle fault diagnosis system for diagnosis, read the fault flash code to 443, the fault is described as "the rail pressure closed loop control mode fault 0 rail pressure is lower than the target value", and use the obstacle detection instrument for the engine working condition. Detection, the read fault is described as "rail pressure control over the upper limit threshold and fuel injection excess"; test car read dynamic data flow, when the fault occurs, the common rail pressure is significantly lower than the set rail pressure. According to the above fault description and data analysis, it is judged that the engine rail pressure is too low. In accordance with the principle of troubleshooting, first, after, after, and then difficult, the engine related parts are investigated. (1) check the oil quantity of the tank. The fuel stock is the total capacity of the 1/4 oil tank (about 100 L). Because the vehicle has no fault, the same fuel stock, the vehicle runs normally, so it is possible to eliminate the low pressure caused by insufficient oil supply caused by oil shortage in the tank. (2) check the low pressure pipeline. No leakage or bending is found in the tubing, so it is possible to exclude the low pressure caused by the leakage or bending of the low pressure oil pipeline. (3) check the low pressure oil pump. The car is maintained in strict accordance with the regulations of the automobile manufacturer, and the diesel filter is replaced regularly. Besides, the car has no fault when the oil quantity is too large and the oil quantity is less. Therefore, it is judged that the low pressure oil pump should not have abnormal wear and lead to insufficient oil supply and the possibility of low pressure oil pump caused by low pressure is excluded. (4) check the tubing of high-pressure oil pump to common rail pipe section. If there are signs of leakage, it can be observed directly if there are signs of leakage, and the possibility of excessive pressure of rail pressure caused by leakage of high pressure oil pipe road is eliminated. (5) start the engine to observe the exhaust emission. If the tail gas is black smoke or white smoke, it indicates that the injector drops oil or the atomization is bad, and the smoke or white smoke of the tail gas is not found, and the possibility that the pressure of the rail is too low due to the leakage of the injector is excluded. From the appearance inspection, the above factors are excluded. According to the phenomenon of "less fuel stock failure" reflected by the driver, it is considered that there are 3 possible reasons: first, when the fuel stock is less, the oil tank oil surface is lower than the oil pump, and the drop caused by the drop causes the difficulty of the oil supply, which is an easy fault in the leakage of the oil pipe road. The two is the blockage of the gas tank vent and the failure of the vacuum inside the fuel tank. Three, when the fuel oil is less, the impurities in the tank and the fuel have a larger density. The absorption of more impurities in the oil pipe sucking process leads to the blockage of the pipeline, which causes the oil supply is not smooth and the rail pressure is too low. Check the leakage of oil pipes again, but there is no leakage in the pipeline; open the oil tank cover for road test, still have a stop feeling when driving, disassemble the oil pipe on the diesel oil water separator, blow the oil into the oil pipe road with the compressed air against the oil direction, and then carry out the road test again after loading, and the failure does not appear again. It is proved that there is a certain amount of impurities in the tank. Troubleshooting: cleaning the tank, when cleaning the tank, there are scales in the fuel oil. Remove the oil suction pipe and release the filter net at the end of the oil pipe. It is found that the glue is attached to the filter network. The blockage of the pipeline is due to the adhesion of these colloids and the adsorption of impurities, and the oil tubing is used in the compressed air when the fault is excluded. The road partially bleed away some adhesive and adsorbed impurities, thus relieving the blockage of the oil pipeline. Remove the filter net to clean it thoroughly, clean up the tank and tubing thoroughly, let the tank keep the stock of diesel in about 100 L, let the vehicle continue to observe, the vehicle run for 2 days, all are normal, confirm the fault is excluded.