A golden cup SY6480AB-MEH passenger car with a mileage of about 150 thousand km. User response: the engine's idle speed is unstable, and its engine is weak. The car is equipped with the JM491 Q-ME engine, the DELPHI multi point electronic fuel injection system, and comes with ECM self diagnostic code reader. When the engine room cover is opened, the engine wiring harness is connected properly, the engine oil is normal, the engine can operate smoothly. After starting the engine, the engine idle jitter is serious and can not accelerate quickly. It is necessary to step down the accelerator pedal slowly to improve the engine speed, the oil warning light shines at high speed, and the oil pressure of the measuring machine is measured. The force is 0.08 MPa, and it is doubted that the engine has multiple failures. After removing the oil pan, clean the sludge on the oil filter, start the engine after changing the oil and oil filter, and the oil pressure idle speed reaches 0.2 MPa, normal. After starting the engine, it is found that the engine idle speed is 950r/min, and the jitter is serious and the engine fault lights on the dashboard. The ECM self diagnosis detector shows that the fault code is P0110, P0105, P0120, P0443, suspected of the previously unscavenged fault code, and the engine fault lights are extinguished after the fault code is cleared and the ECM self diagnostic detector is not. Fault code, but the failure is still. Check engine system with fault detector, normal. The traditional troubleshooting method is adopted to determine the fault location. It is considered that the fault is caused by the poor working condition of individual cylinders. First of all, the test of the lack of cylinder fire, the second cylinder breaking work is obvious, the first cylinder, the 3 cylinder and the 4 cylinder are not obvious, and the spark plug is removed to check the working state of the spark plug electrode. There is no good phenomenon in the 1 cylinder, the 3 cylinder and the 4 cylinder spark plug. According to the maintenance experience, the analysis of the reasons for the failure may be as follows: the mechanical failure causes the insufficient cylinder pressure, the air leakage of the intake pipe, the ignition system fault, the related sensor fault and the fuel system failure. Dismantle the spark plug and measure cylinder pressure of each cylinder, the pressure of the 1 cylinder is 0.89 MPa, the cylinder pressure of the 2 cylinder is 0.89 MPa, the cylinder pressure of the 3 cylinder is 0.88 MPa, the cylinder pressure of the 4 cylinder is 0.89 MPa, all normal, excluding the possibility of the failure of the cylinder pressure. When 4 new spark plugs were replaced, the engine idle speed was 950 r/min, slightly higher, the acceleration performance was slightly improved, the air leakage of the intake pipe was doubted, the throttle, the intake pipe upper body and so on were checked, the seal was well sealed, the intake manifold and the exhaust pipe bolt loosened, the oil exudation at the 1 cylinder exhaust branch was found, and the inlet and exhaust pipe liner was suspected to be broken. Crack, after dismantling, the fourth cylinder inlet interface exhaust pipe liner has fissures, the idling speed is 850 r/min after replacing the liner, the idle speed is still unstable, the acceleration performance is not obviously improved, and the possibility of the fault caused by the leakage of the pipeline is excluded. As a result of acceleration, the ignition system is checked, the resistance of the crankshaft position sensor is 56012, and the connection of the wire connector is reliable. It is found that the crankshaft drive disc signal wheel has friction mark on the other side, thus it is doubted that the fault is caused by the sloshing of the crankshaft drive belt when the engine works, and the auxiliary oil pump transmission belt, the air conditioning belt, and the drive belt are removed. After the generator drive belt, the crankshaft drive belt has a sloshing feeling. When the engine works, the drive belt sloshing is big. After the disassembly of the crankshaft drive belt, it is found that the key slot of the crankshaft drive belt is badly damaged, and the crankshaft drive belt needs to be replaced. The engine's acceleration performance is slightly improved after the replacement, and the idle speed is still unstable. When the engine is working, the cylinder's high tension line is removed in succession to observe the flashover strength of each cylinder. It is found that the strength of the 1 cylinder and the 4 cylinder is weak. Measuring the resistance of high pressure damping line is 2.3 k1Z, normal, measuring the secondary coil resistance of ignition coil, 1 cylinder, 4 cylinder for 4.7 k1Z, 2 cylinder, 3 cylinder resistance 5.2 M, suspected first cylinder, 4 cylinder ignition coil damage, after replacing the ignition coil, each cylinder has the same jumping intensity, the engine idling jitter slightly improved, but still accelerates weakness. In order to verify the data of this fault car related sensor, the measurement of the absolute pressure sensor of the intake manifold is 0.15 V when the intake manifold vacuum is skillful kPa, the 90 kPa is 4.2 V, normal, the throttle sensor signal is 0.5 V-0.9 V from idle to full open, normal, the oxygen sensor signal voltage is 0.3 V-0.8 V, normal, from one positive. The idle motor is removed on the regular vehicle to replace the defective vehicle, and the trouble remains. The oil pressure gauge is attached to the fuel oil rail into the oil pipe. The pressure of the fuel is 0.27 MPa, and the vacuum tube on the fuel pressure regulator is pulled down. The fuel pressure is 0.29 MPa, normal. The injection signal test lamp test, the injector circuit work normally, dismantle the injector and the oil rail assembly, and connect the fuel pipe and the fuel injector connection line, let the injector spray into the large test tube, observe the atomizer of the injector, and find that except for the second cylinder working normal, the other 3 injectors are only 2 in the middle injection hole, and the injection hole 1 It's already blocked. After replacing 3 faulty fuel injectors, the engine is put on trial run and the engine is all right. Fault analysis: using Delphi multi point injection system, the 1 plugging of the injector nozzle will cause the poor working of the cylinder, even the idle idle speed, the failure to accelerate the performance, the system will not have fault code. For the judgement of fuel injector's working condition, it is very effective to use vehicle test method in the absence of special testing equipment. It is an effective method to remove the fault location one by one with the traditional method of troubleshooting and the maintenance experience, which can make the troubleshooting and solve many bending paths.