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A Volkswagen 1. meter 8TSI car with a mileage of over 210 thousand km in 2008. User response: the vehicle sometimes starts difficult, and there are no regular faults. Fault analysis: because of the many reasons that can cause difficulties, it is more complicated to check and start the engine many times. It is hoped that the fault can be reproduced to simplify the diagnosis process. According to the diagnosis idea from simple to propagation, the author first inspects the engine electronic control system, uses the detector to detect the vehicle, and finds out 1 fault codes in the engine control unit: the 08851- fuel pressure regulating valve N276 mechanical fault. Since the fault code is accidental, after debugging the trouble code, the failure code does not appear again. Is the fuel pressure regulator N276 problem causing the engine to start difficult? In order to clarify the diagnostic idea more clearly, it is necessary to briefly introduce the working principle of the engine fuel system of the 1. 8TSI car. As shown in Figure 1, the engine uses a direct injection technology in the gasoline cylinder, and the fuel system uses a high pressure fuel pump (driven by the camshaft) to convert the low pressure fuel in the low pressure fuel system from 50 to 700kPa to 3 to 1. 1MPa of high pressure fuel to meet the needs of different operating conditions. The fuel pressure regulating valve (N276) is installed on the fuel high pressure pump, which belongs to the high-frequency electromagnetic valve (no electricity test). The engine control unit controls the N276 to adjust the duty ratio accurately according to the signal monitored by the high pressure fuel pressure sensor G247 on the high pressure rail, thus obtaining the required fuel pressure. The pressure of the low pressure fuel system is provided by the electric fuel pump in the fuel tank. The fuel pump control unit (J538), which is mounted on the top of the fuel tank, controls the work of the electric fuel pump according to the PWM (pulse width modulation signal), so that the pressure of the low pressure fuel system is maintained at 50 to 500kPa. When the engine starts, the pressure of the low pressure fuel system can reach more than 600kPa, so as to ensure the normal start and work of the engine. According to the above principles, it is known that the engine's normal starting fuel pressure is provided by the low pressure fuel system, so if the high pressure fuel system fails, it generally does not affect the starting of the engine. I have done a normal vehicle test. Even if the N276 plug is pulled out, the pressure of the high pressure fuel system is close to the pressure of the low pressure fuel system. It will not cause the engine to start difficult, and can maintain the engine operation. Only at this time the electronic throttle (EPC) light will light, the vehicle accelerates slowly, and accelerates the pedal. After all, the engine speed is only about 3000r/min, but the vehicle can travel home. Accordingly, the author analyzes the fault of the vehicle and has nothing to do with the fuel pressure regulating valve N276 and the high pressure fuel system. To further verify whether there is any fault in the low-pressure fuel system, the engine pulls down the plug of N276 when the engine is idle, and the engine immediately flameout. The cause of extinction is analyzed: low pressure fuel system can not set up normal engine starting and working oil pressure, which indicates that there is fault in low pressure fuel system. I plug the plug in N276. Repeated attempts to start and stall repeatedly have finally made the engine fail to start again. At this time, the V. A. G1318 fuel pressure tester is connected in the low pressure system, and the ignition switch is opened many times to establish the working pressure. The author finds that the fuel pressure is only 150kPa. Normally, when the engine starts, the fuel pressure should be controlled around 650kPa to ensure the engine's smooth start. The reason why the pressure of the low pressure fuel system is too low is the failure of the fuel pump control unit J538 or the electric fuel pump in the fuel tank. If J538 fails, the relevant fault codes will normally be stored. No such fault code was found in the previous inspection, so the failure of the electric fuel pump was preliminarily judged. Troubleshooting: after the replacement of the electric fuel pump, the engine can start smoothly, at this time the pressure of the measurement of low pressure fuel system is 600kPa, so far, the car does not have this fault again, and the fault is completely eliminated. Fault summary: by eliminating this failure, the author summed up the following experience. 1) when checking the low pressure fuel system of the TSI engine, we can pull down the plug of N276 and observe whether the engine is flameout. If it is extinguished, the pressure of the low pressure fuel system is too low to maintain the normal starting and running of the engine, and the electric fuel pump should be checked to be normal; if the fruit is not flameout, check the data stream 01-08-106 group. The 1 zone value (pressure value of high pressure fuel system), if the value is about 650kPa, proves that the low-pressure fuel system has no malfunction. 2) do not be confused by the fault code in the diagnosis of maintenance. Although the engine system of the car has checked the fault code of the fuel pressure regulating valve N276, it is essentially not a fault of the N276 itself. It is due to the failure of the electric fuel pump and the abnormal pressure of the low pressure fuel system, so that the N276 adjustment to the limit can not make the pressure normal, and the engine control unit is at this time. The fault code on N276 will be stored.