The Buick new century car with an engine model of L46. Customer reflection: the car has been overhauled by the engine in another repair plant. It is not difficult to start, and the power is still available. It is on the road. When the speed rises to 120km/h, the engine fault lights begin to shine. With the continuous rising of the speed or the constant speed of the car, the engine fault lights are changed from bright to light. Long bright. However, after the engine is turned off, it is restarted and the fault lamp is extinguished. If the speed is not more than 120km/h, the fault lamp will not be light again. Fault diagnosis: first of all, road test, failure phenomenon as the customer said. There are many reasons for engine trouble lighting, but the phenomenon of speed is not common. What is the reason that caused the car to light up when the speed of the car reached more than 120km/h? Therefore, the fault code is read out by using the X431 diagnostic instrument: P0300, the engine is out of fire. P0300 indicates that the engine is short of fire. By reading the data flow function, "engine lack of fire data", the current 1~6 cylinder fire loss value is "0", but the history of the lack of fire values, 1, 4 cylinder value of "150". But when the launch of the tear Zheng soft hit 1600r/min, it was found that the number of the 1, 4 cylinder fire loss value increased with the speed, and when the engine speed was stable at 2500r/min, the engine fault lights began to flicker. Through the above observation, the fault found, that is, 1, 4 cylinder work bad, cause the engine. Poor work, discharge of the exhaust more than the standard value, may cause three yuan catalyst damage, PCM detection of the signal, immediately light on the instrument on the launch of the VL fault indicator. Focus on 1, 4 cylinders to find out the cause of failure, so discharge 1, 4 cylinder spark plug, high pressure line, found are all new, still for the 1, 4 cylinder spark plug, high pressure wire, ignition coil and other cylinders to adjust the experiment, the situation is still found. According to the previous experience, the fuel injector is more likely to be blocked, because the vehicle has higher fuel quality requirements and has been repaired many times because of the combustion of inferior oil caused by the case of the lack of cylinder, so the injector was dismantled and tested, and the result of all normal, and the replacement of the injector experiment, the result of the failure is still so . Why does the fault always appear in the 1 and 4 cylinders? And the engine speed over 1600r/min more than the power performance is also very good, no feeling in order to remove the 1, 4 cylinders to eliminate the bad work of the ignition module also changed the new parts, the result of the failure still exist. The ignition system principle and control mode of Shanghai Buick car are analyzed. The ignition system of this car is a waste ignition, that is, the two ends of one ignition coil are connected to two spark plugs at the same time, and the two spark plugs are in the same cylinder of the engine, and the two cylinder pistons reach the top stop point, one is the stop point at the compression stroke, and one is at the end point of the compression stroke. It's the end point of the exhaust stroke. The ignition system of the car is composed of three ignition coils, an ignition module (ICM), a camshaft position (CMP) sensor, a crankshaft position (CKP) sensor on the cylinder, a 24X crankshaft position (CKP) sensor, a related connecting wire, PCM and so on. When does the ignition coil discharge and generate high voltage electricity to spark the spark plug out of the spark? This is determined by the matching signal produced by the camshaft position sensor and the crankshaft position sensor (24X and 7X crankshaft position sensor), and the PCM uses these signals to control the ignition and fuel trigger. PCM not only identifies the signal of the camshaft position sensor, but also identifies the crankshaft position signal, and for the crankshaft position (CKP) sensor, the car has two, namely, 7X and 24X crankshaft position sensors. The 24X crankshaft position sensor is located at the front part of the crankshaft. The sensor is composed of a Holzer effect switch and concentric steel strip flow ring, and is installed on the timing cap. As there are 24 uniform blades and windows on the break ring, 24 open pulses are formed during the rotation of the crankshaft for a week, so it is called the 24X crankshaft position sensor, and this 24X pulse signal is transmitted directly to PCM and PCM to control the fuel and ignition below 1600r/min, especially at low speed and idle speed. Ignition control of the engine. Another crankshaft position sensor for the car is the 7X crankshaft position sensor, which is cast on the crankshaft and has 7 machining grooves, of which 6 are evenly distributed, the interval is 60 degrees, and the seventh slot is 10 degrees to the other slot. With the rotation of the crankshaft, the magnetic field of the sensor coil changes and induction. The alternating current is the 7X crankshaft position sensor signal with a recognition pulse signal. The ignition control module (ICM) receives this signal to control the ignition system, and divides the 7X crankshaft position sensor signal divided by 2 into the 3X pulse signal and passes to the PCM and PCM to receive the 3X signal and confirms the position and rotation of the crankshaft. Speed information, then ignition control and fuel trigger. When engine speed is above 1600r/min, PCM controls ignition control and fuel trigger according to 3X signal and camshaft position (CMP) sensor signal. When the engine speed is above 1600r/min, PCM controls the ignition advance angle and fuel trigger according to the 3X signal and the camshaft position (CMP) sensor signal. Through the understanding of the principle of the ignition system of the car, the fault of the car was analyzed again, because the fault appeared when the engine speed was 1600r/min and the speed of the car reached more than 120km/h. According to the above principles, the failure can be generated by the following several parts: TX crankshaft position sensor, ignition module, engine control module (PCM), crankshaft (position signal tooth of crankshaft position sensor). Because the engine control module and crankshaft have not been checked or replaced before the overhaul of the car, the damage possibility of the engine control module is too small and the engine has been overhauled at the same time. It is doubted that the crankshaft position sensor signal tooth is damaged during the repair process, so the oil bottom is unloaded and the crankshaft is found. It is new. When the signal teeth are checked, there is no damage to the appearance, and there are 7 grooves. But when the angle ruler is checked, 6 of them should have been evenly distributed, but the results are large and small, indicating that the problem is finally found. Troubleshooting: another purchase of a positive engine crankshaft, through the test confirmed that 7 grooves meet the standard, re installed after the test, whether the engine speed or speed, the engine 1~6 fire value is "0", the fault light does not flash, repair completion. Summary of the matrix: repair vehicles must use qualified accessories; before repair, we must carry out detailed inquiring, to understand the causes and consequences of failure. To clean up the fault, we should not only pay attention to the part of the circuit, but also pay attention to the mechanical components, especially the sensor. Besides the sensor body, the precision of the signal gear ring must be checked.