A Chevrolet mileage with a mileage of about 1600km. The owner reflected that the car had been running from 100m to the traffic lights after refueling at the gas station and was unable to restart. Fault diagnosis: this vehicle is equipped with 2.0L ECOTEC straight row 4 cylinder aluminum engine, code LTD. The rescue scene found that the spark plug was not ignited when it was not ignited, and the tachometer was not moved at startup; it was found that the rotating speed signal was zero at the start of the GDS2+MDI inspection, and the crankshaft position sensor found that the sensor was broken (as shown in Figure 1). The cylinder block near the installation hole of the sensor broke a hole in the egg big, and the crumps had a striking mark on the pieces. Trace, from the inward observation of the hole, the rotating crankshaft was found that the connecting rod was completely broken and the piston stayed near the top and stop point; the 4 cylinder piston top gasoline was detected by the dismantling spark plug, and the air filter was checked without any trace of water, and there were no external impact marks in the front and lower parts of the vehicle. . The causes of the fracture of the engine connecting rod are as follows: 1. the intake of the engine cylinder (combustion chamber) leads to the fracture of the connecting rod of the engine. The engine sucks water into the cylinder when the vehicle is running on the road where water is accumulated. Initially, the water entering the cylinder will soon form hydrated gas under the action of high temperature of the cylinder block, so that the cylinder can not form a combustible mixture. As the amount of water increases, the water will accumulate on the top of the piston, reducing the effective volume of the chamber, increasing the compression resistance, and increasing the pressure of the piston to the connecting rod. When the amount of water is up to a certain extent, the compression stroke actually becomes the compression of water. The pressure of the connecting rod increases sharply, so that the bending deformation is even broken until the engine block is broken. Because the intake of the engine cylinder and the engine speed determine the pressure of the connecting rod, it is not all of the engine cylinder when the connecting rod is inflow and the connecting rod will break immediately. To confirm that the engine connecting rod fracture is due to the intake of the engine cylinder, it can be confirmed by the following methods: (1) whether the air filter is wet and the soil is attached to the air filter, and whether there is water on the air filter shell and the inlet pipe wall. (2) check the engine oil to determine whether the engine cylinder is inflow. After the engine is flooded, the oil around the engine cylinder cover and intake and exhaust valve seats will appear milky white, which is the result of mixing water and oil. (3) check the piston and connecting rod to confirm whether the engine is water. The engine connecting rod is broken due to the intake of the engine cylinder, and the top of the broken piston rod will be very bright (relative to the top of the piston without fracture). And the broken connecting rod is curved. In addition, we can also find that the top stop point of the piston ring on the cylinder liner can be found to be obviously lower than that of the other cylinders. This can also help us to determine that the connecting rod is broken when the connecting rod is curved. 2. abnormal engine fuel injection system leads to fracture of connecting rod. This usually results from the continuous injection of fuel injectors in a certain cylinder of the engine. Often there will be difficulties in starting, idle jitter, exhaust pipe black smoke, power down and so on. After the dismantling, it can be judged by observing the combustion of each cylinder. The cylinder and the cylinder head of the cylinder and the cylinder cover will be blacker than the other cylinders because the fuel mixture is thicker than the other two. At the same time, the fuel injector and the fuel injection control circuit can be further checked. The 3. connecting rod is locked with the crankshaft resulting in fracture of the connecting rod of the engine. This is usually caused by poor engine lubrication, which can be judged by checking the wear of engine parts. The 4. connecting rod itself has a problem. In general, it can be determined by the analysis of chemical composition of the connecting rod material, hardness test, metallographic examination, scanning electron microscope fracture analysis and so on. The possible reason is that the low stress fatigue fracture caused by the quenching micro crack, the pearlite + flake, the super size nonmetallic inclusions and the bulk ferrite in the structure cause the mechanical properties and the fatigue life of the connecting rod to decrease. 5. improper operation of maintenance operation. For example, the cleaning solution is not cleaned when the soaking process is cleaned, leading to the restarting of the engine's top cylinder; for an engine equipped with a variable intake port system, if the flow of the cleaning agent is incompatible with the engine speed when the intake system is not cleaned, it may lead to an excessive amount of cleaning agent in the intake manifold. Tired, when the high speed running, the long intake port is changed into a short intake port, and the cleaning agent in the intake manifold instantly inhaled the combustion chamber to cause the cylinder. 6. the oil in the oil bottom is inflow into the air filter, the intake manifold and the inlet. After the engine starts, a lot of oil is inhaled into the combustion chamber. During the compression process, the piston is not compressed, the pressure on the top of the piston increases and the rod is bent and deformed, and it passes the long time of the user. When driving at high speed, the connecting rod suddenly appears fatigue fracture; it can be judged by investigating whether there is a turning accident record, checking whether the air filter has oil, and the abnormal characteristics of the piston ring height trace. 7. the damage of the crankcase system leads to the oil top cylinder. For an engine equipped with a variable intake port system, if the diaphragm type crankcase ventilation valve breaks, it may cause a large number of oil to be continuously inhaled into the intake manifold, and gradually accumulate, change into the short intake port at high speed, and the oil in the intake manifold is instantly inhaled into the combustion chamber leading to the top cylinder. Because the mileage of the car is less than 2000km, from no maintenance, no engine maintenance, there is no wading experience, there is no overturn accident, so the gasoline test is first carried out according to the requirements of the host's claw. The test result is that most data indicators conform to the national standard, and there is no correlation between the exceeding standard items and the fracture of engine connecting rod. Further dismantling after authorization by the owner and the host plant. Remove the oil bottom shell and find that the oil bottom shell corresponds to a small pile of a small pile of aluminum cylinder in the position of the 4 cylinder, and the 4 cylinder connecting rod bearing cover is removed. There is no problem of bolt fastening torque. The connecting rod bearing has no abnormal wear or aspiration; the connecting rod has no obvious bending, the fracture section is V shaped, and the upper half of the rod can be flexibly rotated on the piston pin. Axial sliding, no locking and locking phenomenon; comprehensive analysis of the cause of the failure is the abnormal fracture of the connecting rod material or machining defects. Troubleshooting: change the engine assembly after the test, everything is normal, no engine jitter, smoke smoke phenomenon, indicating that the engine injection system has no abnormal, troubleshooting.