When the engine fault is overhauled, especially when the engine idling jitter is overhauled or the exhaust emission exceeds the standard, the maintenance personnel often meet the fault diagnosis instrument to prompt the engine to be missing, so we should have a correct understanding. After the engine is out of fire, high concentrations of hydrocarbons will enter the exhaust system, resulting in excessive emissions. The high concentration of hydrocarbons will also increase the temperature of the three way catalytic converter, which will damage the three yuan catalytic converter seriously. The following is a case study of the engine failure of TOYOTA. (1) in order to prevent the exhaust emission exceeding the standard and the heat damage of the three element catalyst, the engine control unit uses the crankshaft position sensor to monitor the deviation of the engine rotation speed rate to determine the lack of fire, and the camshaft position sensor is used to identify the fire - deficient cylinder. When the engine misfire rate exceeds the threshold and may lead to excessive emission, the engine control unit starts to count the number of engine fires. (2) a classified engine lack of fire can be divided into two cases, one is complete lack of fire, that is, no combustion, the other is partial fire, that is, combustion instability. OBD II defines three types of engines, namely, A, B and C. (1) A type fire is the most serious fire failure, which is close to three yuan catalyst damage. If detected, the engine fault warning light will flicker, prompt the driver to repair immediately, and store the fault code and data frame according to the first stroke logic. The engine diagnosis system identifies the A type fire by counting the number of times of fire in the 200 turn of the engine crankshaft. 2. When the B type fire occurs, the emissions of harmful substances in the exhaust gas will increase by more than 1.5 times. (3) C type fire is the lowest degree of lack of fire, which will cause vehicle emission to fail. The engine diagnosis system identifies the B and C type fire by counting the number of missing fires in the 1000 rotation of the engine crankshaft. The B and C type fires occur continuously in the two stroke, and the engine control unit will store the fault codes and light the engine fault lights. An engine with correct air fuel ratio, sufficient ignition and good mechanical condition will not cause a fire. If there is any problem in one aspect, the combustion will end prematurely, resulting in a lack of fire. (3) in the process of eliminating engine failure, it is necessary to pay special attention to 3 points, i. e. cylinder pressure, ignition and fuel injection. Cylinder pressure: the use of cylinder pressure meter can be easily detected and no longer described here, but it is difficult to detect the change of the hardness of the valve spring and the wear degree of the camshaft when the cylinder pressure is measured, and it is also necessary to consider whether the intake volume is enough (air leakage or valve carbon). Ignition: for the maintenance of engine fire, sometimes only by reading the engine data flow can not be found, but also with the use of oscilloscope to make a further judgment. The factors that should be taken into account include the timing of ignition, the normal operation of the spark plug, the standard value of the high voltage line, the normal operation of the ignition coil (whether the power line and the signal line is connected), and the normal operation of the engine control unit (including the signal provided by the CAN data). It is suggested that the instrument test (Figure 1) should be used as far as possible. For example, the synchronism of the camshaft sensor and the crankshaft position sensor can be checked by an oscilloscope. The existence of the fire and the accuracy of the ignition timing and the phase of the gas distribution can be analyzed. The working condition and ignition time of the ignition coil are checked with an oscilloscope and the spark plug can be analyzed. It is good or bad to check the connection between the data lines of each control unit with an oscilloscope, detect the resistance of the spark plug with a megabymeter, and detect the resistance of the high voltage line with a multimeter. (3) injection: one is to look at the pulse width, ignition time and the working condition of the oxygen sensor through the data flow. Two is to check the synchronization between the throttle position sensor TPS and the injector with an oscilloscope, check the synchronization between the TPS and the oxygen sensor, and then check the synchronizing of the fuel injector and the oxygen sensor. Check the changes of the fuel injector and oxygen sensor). Finally, check the individual waveform of the injector, analyze the quality of the injector and the length of the injection time (compared with the standard waveform). Finally, the gasoline labeling, the detonation sensor and the three element catalyst should be considered. Many maintenance stations like to use the method of changing parts to check fire failure. Although the author does not recommend this, sometimes it can also quickly troubleshoot faults. If the replacement method is used for inspection, it is recommended to use the following replacement method. For example, 1 cylinders of fire, we can replace the 2 cylinder line and 1 cylinder, the 3 cylinder injector and it change, the spark plug can be exchanged with the 4 cylinder, so after the replacement, we try again until the fault occurs again. If the fault becomes a 2 cylinder fire, it is a problem of cylinder line, for example, the 3 cylinder fire is the problem of injector, and so on. If the fault is not transferred, mechanical failure or other component failures are considered. In fact, the failure maintenance of the engine is not complex, usually the failure of the ignition system is more, and sometimes the fault point will appear in the mechanical aspects or the engine control. Below, the author combines 2 specific failure cases to briefly explain the maintenance of fire failure. Case 1 malfunction: a 2003 year TOYOTA grand tyrant multifunction vehicle equipped with 2AZ-FE engine. Users reflect the engine idling after morning driving. Inspection and analysis: observe the car leaving the factory for a night, and the engine idling on the morning of the second morning. Using TOYOTA intelligent tester, no engine fault code is stored. The engine data flow is checked and the 2 cylinder is missing. After exchanging the 2 cylinder and 3 cylinder ignition coil, the 2 cylinder fire warning disappeared and the 3 cylinder appeared fire. Troubleshooting: the analysis of the author is that the 2 cylinder ignition coil is not working well under the cold condition. After the replacement of the 2 cylinder ignition coil, the idling jitter phenomenon of the engine disappeared. Case 2 malfunction: a 2006 year TOYOTA corolla sedan, equipped with 1ZZ-FE engine. The user reflects the engine fault lights and the engine quiver at idle speed. Inspection and analysis: using TOYOTA intelligent detector test, the engine fault code is P0304 (detection of the engine fourth cylinder fire), check engine fire data frame is: engine speed 724r/min, the total number of ignition times 391 times, the engine 4 cylinder fire frequency 4 times. The engine was basically checked, but no problems were found. The ignition coil, spark plug and fuel injector are replaced, but the engine is still missing. It is doubted that the engine intake and exhaust system has problems, and the pressure of the cylinder is measured. The pressure of the 1 cylinder, 2 cylinder and 3 cylinder is close to 1.4MPa, and the pressure of the 4 cylinder is 1.2MPa, although 0.2MPa is smaller than the cylinder pressure of the other 3 cylinders, but it is also within the normal range of difference. Finally, the exhaust gas analyzer is decided to further check the intake and exhaust system of the engine. In order to meet the stringent requirements of emission regulations and zero emission of harmful gases, such as HC, CO and NOx, the modern engine control system must always control the actual air fuel ratio near the theoretical air fuel ratio 14.7:1 (that is, the excess air coefficient is always 1). When the engine is measured at idle speed, the components of exhaust gas are as follows: CO2 is 9.94%, O2 is 8.09%, HC is 596 x 10-6, CO is 0.784%, NOx is 0 x 10-6, and excess air coefficient is 1.5. When the engine speed is stabilized at 3000r/min, the excess air coefficient is close to 1, which indicates that the control system of the engine at high speed is basically normal to the actual air fuel ratio. I suspect that when the engine is working, there is air that has not passed the air flowmeter into the cylinder, causing the mixture to be too dilute at idle speed, so that the excess air coefficient is greater than 1. Remove the valve chamber cover and check the valve as normal. Check the clearance of the inlet and exhaust door, and find out that one of the 2 exhaust valves in the 4 cylinder has no clearance, which is always on the camshaft, causing the valve to be unable to shut down, and the air leakage has been existed all the time. Dismantling the cylinder head of the engine and finding that the valve seat of the exhausting exhaust valve always sinks. Troubleshooting: repair the exhaust valve seat of the 4 cylinder sinking of the engine, and replace the 4 valves and the 4 valve and the cylinder cover of the 4 cylinders, and all the 16 valve seals for the cylinder cover.