A FAW 2.5 L car with a mileage of over 240 thousand km and equipped with a 5GR engine in 2007, TOYOTA. Users reflect: the engine of the vehicle has no regular flameout during driving. Inspection and analysis: the defective vehicle was towed to our factory by a rescue vehicle. The maintenance personnel tried to start the engine after receiving the car, and found that it could start normally, but the idle speed was about 10s or so. After starting the engine, step on the accelerator pedal, the engine speed rises slowly, and then gradually extinguish. "Ask the user to know that the car often appears in the near future engine stall phenomenon, after the fire starts again the engine, but also can drive normally. But after this fire, the engine could not operate normally. Connect TOYOTA special fault diagnosis instrument to detect, no trouble code storage. The main parameters of engine data flow, engine speed, throttle opening and air flow were sensitive and consistent, and no abnormalities were found. Connecting fuel pressure gauge to detect fuel pressure, found that the pressure gauge reading from the engine just started 250 kPa gradually reduced to 0 kPa, the engine then flameout. A multimeter is used to detect the power supply of the fuel pump. When starting, there is a 12V voltage, and the voltage will disappear after starting. At this point, the failure of the diagnosis was due to no working voltage of the fuel pump at idle engine condition. According to the control principle of the fuel system of the vehicle, in order to adapt to the different demand for the fuel supply when the engine is starting, the large load and the small load, the unnecessary mechanical wear of the fuel pump is reduced, and the speed control is taken to the fuel pump. When the engine is started, the starting (STA) signal and the crankshaft position (NE) signal are entered into the engine control unit (Figure 1), and the Tr 1 in the control unit is connected so that the C/OPN relay is absorbed. The F/PMP relay is a normally closed relay. The power is relays to the fuel pump through the F/PMP relay. The fuel pump starts working at high speed. When the engine is running at idle speed, the NE signal is continuously input into the engine control unit. While the Tr 1 is connected, the Tr2 is connected. The F/PMP relay is switched off. The power supply can reach the fuel pump only by the additional resistor, and the fuel pump operates at low speed. When the engine is running at idle speed, the C/OPN relay is measured with a 12V voltage by a multimeter, and the terminal of the fuel pump resistor also has a 12V voltage, but the other end has no voltage output. The resistance of the fuel pump resistor is measured. Thus, when the engine is in idle speed, the FIPMP relay is disconnected and the fuel pump resistor is broken. The fuel pump will stop working because of the loss of the power supply. The engine can only maintain the operation of about 10s by the pressure of the high speed operation of the fuel pump when starting. Troubleshooting: replace the fuel pump resistor, repeat the test run, engine idle speed is stable, fuel pressure is stable, acceleration is strong, troubleshooting. Review and summary: for the maintenance personnel, the important premise of diagnosis and troubleshooting is to master the work principle of the whole system and to combine the practical experience to analyze the fault phenomenon synthetically so as to quickly confirm the fault sound and eliminate the fault.