In the 1993 Shanghai Santana GX car equipped with IV type carburetor engine, it is more than 310 thousand km, which is difficult to start in 1993. The exhaust pipe "sudden and sudden" sound appears in the car, and it is more obvious at high speed. Troubleshooting: (1) cause of failure analysis of the cause of this failure: a few cylinders are not working, sparks are too weak and cause a lack of fire, excessive mixture of gas or too thin. Possible faults include ignition coil, distributor and high voltage wire, electronic igniter, gasoline pump, carburetor, gasoline filter, etc. (2) the troubleshooting method checks the working conditions of each cylinder, the results are all normal, and the carburetor oil surface is normal. Pull out a cylinder and separate cylinder high voltage line to test the fire and find that the spark is weak. Therefore, judge the fault in the ignition system. When the ignition switch is switched on, the power supply voltage of the ignition signal generator ("+" and "-") is measured between the "+" and "-" with a multimeter DC voltage file to be 10. 2V; the detection signal voltage ("S" and "-") when turning the distributor is swinging between the 10. 2V and the 0.4 V, indicating that the ignition signal generator in the distributor is normal. The voltage between the ignition coil "+" and "-" is detected by a multimeter DC voltage file. When the ignition switch is connected, the voltage drops rapidly from 7V to 0, which indicates that the switch transistors in the electronic igniter can quickly turn off at the moment of the ignition switch on, and the electronic igniter is basically normal. Check the initial and secondary winding resistance of the ignition coil, also in the normal range, and check the vacuum and centrifugal ignition advance voltage regulator on the distributor. No anomaly is found. Finally, the resistance between the central conductor and the tip electrode is found to be infinite, and the normal value should be about 1 K Omega. It is a broken fire conductor, which causes the ignition voltage to be too high. (3) troubleshooting measures to replace the new distributor, start the engine smoothly, speed up is also normal, troubleshooting. Fault analysis: the distributor in the Santana sedan distributor is somewhat different from that of other cars. It has a resistance of about 1 K Omega. The resistor is in a state of circuit breakage, which leads to high ignition voltage, and the ignition system is short of fire from time to time. The fault engine can start and operate, indicating that both the ignition signal generator and the electronic igniter can work. Therefore, the possibility of failure of the ignition signal generator and the electronic igniter is very small, while the fault is first checked by the ignition signal generator and the electronic igniter, so the troubleshooting program is not very reasonable. In addition, the method of checking the electronic igniter and judging the fault or not is not appropriate.