A 3.1L engine equipped with fuel injection system belongs to throttle body injection (TBI) Chevolet Lou Mina car. The car stalled during the 1 long-distance run and could not start again. Fault diagnosis: 1. check the car, start the engine, the starting machine runs forcefully, the cylinder pressure is normal, the spark plug is used as the fire test, the spark is strong and it is slightly blue. 2. With the upper cover of the air cleaner, you can see that all 2 injectors are free of oil, and the carburetor cleaning agent is injected into the throttle body. 3. check the oil tank, release the tubing and measure the normal fuel pressure. 2 injector connector is pulled out, and each injector has 1 terminals for battery voltage after opening the ignition switch. The engine is started and the control terminals of the 2 injector are all without pulse iron signal. The measurement of the ECM connector and the control terminal of the injector is 0.02 Omega, and there is no short circuit on the positive pole. 4. it is normal to measure the ECM supply voltage and the grounding power, and the contacts of the connectors are good, and there is no loosening phenomenon. The problem seems to be that the engine control module has no output injection pulse, or it does not receive the signal of fuel injection. Because at that time, there was no maintenance information of the vehicle, and there was no special testing equipment at hand. It suddenly occurred to me that the car was relatively messy because of its earlier age, and seemed to have something added to it. 5. It was found that the car battery negative electrode installed 1 large breakers between the body and the engine, measuring the pressure drop of 0.3V, and measuring the negative resistance of the body and battery to 15 Omega, and the resistance between the engine and the engine to 32 Omega. 6. then remove the broken electrical apparatus and reorganize the iron line on the body and the engine. After the treatment, the resistance between the negative electrode of the battery and the engine and the body is measured to be 0.03 Omega. Loading the negative cable, starting the vehicle, a successful start, the ignition restart the engine, normal operation, multiple start no abnormal discovery, sloshing each line harness connector, the engine has no abnormal phenomenon, the fault has been ruled out. On the second day, the car was started, everything was normal, but the 10min was automatically extinguished, and the car was unable to start again. Check the reason, the fault is the same as before, or there is no oil, originally thought that no fuel injection is due to poor iron, now it seems that the real reason has not been found. As the car belongs to the throttle body injection, the key signal to determine the fuel injection should be the intake pressure sensor and the throttle position sensor. 7. the signal voltage of the throttle position sensor is measured after the engine ECM connector is measured. When the ignition switch is opened, it is 0.6V, which increases with the opening of the throttle. The maximum can reach 4.5V. The signal voltage of the intake pressure sensor is 3.2V, the starting vehicle jumps between 1.2 and 1.3V, and the starting signal received by the engine ECM is normal. . 8. at this time remember that the engine failed to light, the dismantling instrument found the light bulb has been damaged, replaced 1 indicator light bulbs, open the ignition switch, the fault light light, 5S after the extinguishing, show the system failure, immediately start the vehicle, the vehicle actually started the car. Flameout, start the engine again, start smoothly, idle speed and acceleration are normal, immediately realize that the fault is hidden again. 9. just then found the original vehicle data about the fuel injection system, found the self diagnostic connector on the left side of the steering column, connected A and B 2 pins with test traverse in the case of ignition switch off, opened the ignition switch, and the fault lamp flashed the number 12 fault code, indicating the storage of no cause barrier. 10. compare the circuit diagram and the working parameters of the ECM terminals. In general, this intermittent fault should not be a problem on the line, but it should be caused by the intermittent work of electronic circuits, but the failure rate of ECM is minimal under the influence of external force or special conditions (such as damp or high temperature). 11. open ECM, its internal circuit board is intact, no water, corrosion, erosion and other abnormal signs, at this time the maintenance work is in trouble, have to restart the test car, so that the fault recurrence. 12. sure enough, after nearly 1h of the trial run, the engine suddenly failed and failed to start. The malfunction was exactly the same as before. The working parameters of the ECM pins are measured again. When the B5 foot Purple / white line connected to the ignition module is measured, the anomaly is found. The normal operating voltage should be 0V when the ignition switch "ON", and the engine is running at 1.3V, and the voltage is 0.01 V at this time. Find its ignition control circuit diagram (as shown in Figure 1). The car ignited for the distributor, and there were 1 separate ignition modules in its distributor. There were 7 terminals on the module, of which P, N was induction coil, E was the ignition timing correction of ECM, R was the reference voltage signal number, and "+" was the ignition switch "ON" power supply. The C is the negative control terminal of the ignition coil, and B is the by-pass circuit signal. According to the analysis, the E terminal is only a correction signal to the ignition timing of ECM. In the early general car system, its module itself can complete the ignition process. The ECM can correct the timing of the ignition when the engine speed exceeds 400r/min; the B foot is a bypass circuit signal, and the B terminal is set by the timing set connector. The ignition timing can be stopped by ECM, and the rest of the feet will not affect the fuel injection system. The only suspect is the ignition reference signal of the R foot. According to normal reasoning, its ignition reference signal should actually be the 1 ignition confirmation signal transmitted by the ignition module to ECM. 13. disassemble the distributor cover, touch the ignition module with hands and feel hot. Check the terminals and no bad contact. After the ignition module temperature drops, the distributor is installed and the car is started once. At this time, the R line is disconnected, the injector stops injecting oil and the engine is extinguished. 14. restart the engine again, measure the voltage of the R foot Purple / white line ignition module on the side of the ignition module of 1.3 to 1.5V, and at this time the engine presents the failure phenomenon of the fire without oil and can not start, so it is determined that the ignition module is bad for the ignition module and can not start with the fire without oil. After the replacement of the point fire module, the fault is ruled out. Maintenance summary: the main fault is to ignore the impact of the ignition system on the fuel injection system. It is considered that the fuel injection system should control the fuel injection if the ECM receives the starting signal as long as the intake pressure and the throttle position signal are normal. However, in the western countries that attach importance to the emissions, even in the earlier models, they also put the ignition as the first condition to determine the fuel injection, and in the early stage of the control module, it did not set the circuit out of the corresponding fault code, and the number 42 ignition control circuit appeared in its fault table. Code, also only for E foot ignition timing correction circuit and B foot bypass circuit failure. From this, it is not surprising that there is no trouble code in the control module.