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The normal start of a car engine must have three elements: compression, spark and mixed gas. If a certain element is abnormal, it will cause the engine to be unable to start or start. Starting failure is usually difficult to start and start. Difficulties in starting are divided into cold start difficulty and hot start difficulty. The engine can not start and no ignition sign, usually due to no fuel injection. The main reasons are as follows: 1. The engine speed of the speed signal system and the crankshaft position sensor detect the speed signal, provide the crankshaft position signal when the engine works, and take the control system as the control system. If the sensor or its line fails, the electronic control unit can not receive the speed signal and the crankshaft position signal, and the fuel injection and ignition timing can not be properly controlled. The injector does not move and the spark plug does not jump fire. Check with the stethoscope and timing light to confirm whether the injector and spark plug are working. When the above fault occurs, the fault code can be displayed in the general self diagnosis system, and the speed sensor, 1 and 2 camshaft position sensors and their lines are inspected in an all-round way. First disconnect the sensors of the wiring, check their resistance, if the resistance is abnormal, it must be replaced; if normal, then check whether the wiring and wiring device of the ECU and the sensors is normal. 2, fuel pump and control circuit failure, if the fuel pump or control circuit failure, it will cause fuel system no fuel pressure. Even if the injector works properly, the fuel can not normally be injected. The inspection method is: diagnose the plug +B and FP with the short connection connection and then connect the ignition switch to check the pressure in the oil intake hose. If there is pressure in the hose and can hear the sound back, it indicates that the fuel pump itself has no problem; otherwise, the fuel pump should be checked, the resistance between the 4 and 5 of the measuring terminals can be measured, such as and the regulations. The fuel pump should be replaced. If the fuel pump works well, the control circuit should be checked, including fuse, EFI main relay, fuel pump relay, resistor and various wiring and wiring devices. 3. The fuel pressure of the fuel pressure regulator fuel system has a direct effect on the concentration of the mixture. Therefore, the fuel pressure should be checked first. The method is: first put the fuel pressure gauge into the fuel line, then start the engine and measure the fuel pressure. If the fuel pressure is too high, the pressure regulator should be replaced. When the pressure is too low, the palm oil hose can be clamped. If the fuel pressure rises to the normal value, the fuel pressure regulator is damaged, otherwise the fuel pump and the fuel can be checked and burned. Oil filter. After stopping, check the fuel pressure should be kept at the specified value of 5min, otherwise it will explain the leakage of the injector and cause the mixture to be too thick. 4. When the fuel pump and the fuel filter are difficult to start, the ordinary fuel pump can work normally. The problem is that the oil pump filter screen plugging so that the oil pump can not be fully inhaled or the fuel filter is not smooth and the pressure of the oil supply system is insufficient. 5. Cold start system failure. In some vehicles, cold start injector is used to increase the mixture gas during cold start to improve the cold start performance. The cold start fuel injector is controlled by the start switch and the thermal time controlled switch. The duration of the fuel injection depends on the heating coil current and the temperature of the cooling water. Emergency measures: the diagnosis of the above faults should follow the principle of "first power after the machine" and "first after simple". The reasons for the cold start failure of EFI are mostly intake valve back, excessive carbon deposition in intake manifold, and too many impurities in the fuel injector. If the above failure occurs on a new car, such as a car with a mileage within 60 thousand kilometers, it is suggested that the user do not clean the engine when the vehicle runs 2-3 kilometre. In addition, the engine should take a higher speed to make the dissolved gelatin and coke burning from the tail gas at high temperature after the removal of the free cleaning. After the dismantling and dismantling of the vehicle, the vehicle is placed on the second day in the morning, and the valve is dissolved by the colloid adhesion. It is more difficult to start and the engine idling more jitter, that is, the commonly known "sticky valve" phenomenon. Once this phenomenon occurs, it needs to be re removed and cleaned.