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A 2007 three compartment Fawkes car runs smoothly after the engine starts, and the car wobble after a distance. Fault maintenance: first times the failure, in a repair plant repair, the plant replacement spark plug, the failure phenomenon disappeared, running for nearly 600km (1 months) after the failure. The second time for another repair plant to repair, the factory changed the high voltage ignition coil, when the problem was solved, driving for half a month, after about 300km, the fault recurred again. The third time to repair the repair plant again, the factory changed the ignition coil, the failure phenomenon disappeared, but 3 days later, the fault recurred. When the owner was almost depressed, he tried to come to our repair shop by introducing his friend's feelings. Fault detection: the first step: read the fault code with the 431 decoder, and the trouble code shows the multi cylinder fire. Analysis: cylinder misfire is a common fault of multi cylinder engine, its detection and diagnosis is a necessary part of the car fault diagnosis function. However, there are many reasons for the fire failure, such as ignition system (spark plug carbon, ignition energy reduction), low pressure in cylinder due to gas leakage and so on. In reality detection, it is impossible to detect every fault source that produces fire phenomenon. The possible causes of multi cylinder fire failure are: individual cylinder high pressure separation or damp leakage; individual spark plugs damp, excessive carbon deposition or insulator damage leakage; spark plug electrode gap is too small or too large; cylinder pressure is low, valve seal is not strict, piston ring wear is serious, cylinder washer ring damage and so on. Multi cylinder fire detection circuit, ignition system, oil supply system, oxygen sensor, cylinder pressure, throttle position sensor, crankshaft position sensor, water temperature sensor and so on. Although the fault shows multi cylinder fire, it is possible that only 1 cylinders are not working, and the other cylinders are working normally. The second step: using the infrared thermometer to test the exhaust pipe temperature, it is found that the working temperature of the second cylinder is very low, and the combustion temperature is not shown. It is preliminary to judge that the work of second cylinders is not normal. Analysis: infrared thermometer plays an important role in product quality control and monitoring, on-line fault diagnosis, safety protection and energy conservation. In the past 20 years, the non-contact infrared thermometer has developed rapidly, the performance is perfected, the function is constantly enhanced, the variety is increasing, the scope of application is expanding, and the market share is increasing year by year. Compared with the contact temperature measurement method, the infrared thermometer has the advantages of fast response time, non-contact, safe use and long service life. In addition to measuring the temperature of the exhaust pipe, it can be judged by other methods, such as the short circuit of the spark plug in the cylinder by a screwdriver. If a cylinder is short circuited, the vibration of the engine increases, and the more obvious abnormal sound is heard from the exhaust pipe, indicating that the cylinder is working; if there is no change in the engine, the cylinder does not work, The fault comes from the cylinder. The third step: using the exchange normal working cylinder and the second cylinder ignition coil method to detect, it is still determined that the second cylinder does not work. Analysis: this step shows that the ignition coil of the second cylinder is all right. The fourth step: remove the spark plug check on the 2 cylinder, spark plug color is normal, ignition is normal. Analysis: the general method of checking spark plug: remove the spark plug with high pressure line, make the end off the spark plug 5 ~ 7mm, look at the spark situation. If there is no fire, the fault is in the distributor, and the distributor should be checked: if the wear of the cam is not equal, the shaft (shaft sleeve) is worn loose or the socket outlet is leakage, the electricity is electric, the rust pollution of the seat hole is too much conduction. Well, it should be repaired or replaced. If there is fire, remove the spark plug check: if carbon deposition is too much, the electrode gap does not meet, it should be cleaned, adjusted or replaced; if the insulator is damaged, leakage should be replaced. This step shows that the second cylinder spark plug is not a problem, but according to the owner's reaction, why will the failure of the spark plug and the high pressure ignition coil be replaced temporarily in the first few times? The fifth step: after using the computer to remove the fault code, it starts again, the fault phenomenon vanishes, the engine runs smoothly, and the fault is reappeared after 3min. Analysis: in order to further check the fault, read the trouble code again or show the multi cylinder fire. The sixth step is to check the ignition line with Multimeter without detecting the circuit breakage and short circuit. Analysis: ignition system includes spark plug, high voltage ignition coil and ignition circuit. The spark plug and the high voltage ignition coil are normal, so the ignition line is detected. The seventh step: access to the gasoline pressure gauge, the gasoline pressure is normal, and the fuel injection quantity and atomization are normal with the nozzle cleaning tester. Analysis: preliminary judgment, the oil supply system is no fault. The eighth step: detect cylinder pressure, cylinder pressure display 13kPa, normal. Analysis: the purpose of this step is to eliminate mechanical problems and make sure that the valve guide does not issue cards. According to maintenance experience, similar problems have been encountered. The ninth step: inserting the 2 cylinder injector connector with the light emitting diode, starting the engine, the light emitting diode scintillation frequency is normal, indicating that the injector signal is normal, after 3min, the light emitting two stage tube is not bright, and the injection signal is interrupted. Measuring the line voltage of injector with multimeter is more than 12V. There is no pulse signal to the signal line to the computer. Analysis: the light emitting diode inserts the injector connector, which is mainly to measure the voltage and signal of the injector. If the light emitting diode is always on and does not flicker, it indicates that the pulse signal line is often connected or cast iron; if it is not bright, the injector voltage is abnormal or the pulse signal is abnormal; if the light emitting diode scintillating, it shows the injection. The voltage and pulse signal are normal. The on-off of the current is controlled by the pulse signal emitted by the electronic control unit (ECU). The tenth step: test the second cylinder injector to the ECU line. After testing the resistance is normal, there is no break, indicating that the circuit is normal. Analysis: resistance is normal, indicating that there is no circuit breaker. Through the above test, the cause of the fault can be reduced to 2 problems: the contact between the circuit plug is not good and the ECU fault. Fault analysis: 1. because the single cylinder is not working, it can exclude the possibility of the crankshaft position sensor, water temperature sensor, throttle position sensor and oxygen sensor fault. The 2. decode instrument shows the multi cylinder fire. After the exchange test, the spark plug and the high voltage coil can be eliminated. Then the ignition coil is tested normally to the ECU line, and the problem of the line is excluded. 3. through the gasoline pressure gauge test, remove the problem of gasoline pressure; after the injector test, eliminate the fuel injector problem. 4. consult the data, study the relationship between ignition and fuel injection of the electronic control engine, the ECU has repeatedly received the unsuccessful ignition signal, which will break the oil, that is, the function of breaking the oil automatically. The purpose is to not allow too many unburned fuel to enter the three element catalyst and avoid the damage of the three element catalyst. The computer self diagnosis system does not receive the injection pulse signal, and it displays the fault code of multi cylinder misfire. Troubleshooting: after the above analysis, the fault should be in the ECU control system. Disassemble the ECU, test the control line of the second cylinder injector through the multimeter, the resistance is normal, and then the eye is carefully observed by the naked eye. It is found that the color of the triode that controls the second cylinder injector is darkening, and there is a great deviation from the other normal colors. Replace the transistor, use the decoder to remove the trouble code, restart, and eliminate the fault. Through the road test, the fault will no longer appear, accelerate the normal operation and balance the engine. After a period of time, the owner failed to respond to the failure. Fault review and summary: Why are we being played by computers for this failure? Let the owner spend a lot of money? It is because: first, we do not understand the electronic control engine has broken fire to have the function of oil breaking protection; second, do not understand ECU without pulse signal, the computer self diagnosis system record multi cylinder fire enemy barrier; third, do not understand the function and principle of the three pole tube which is controlled by the injector in the control of the injector, and it subtly covers the matter. The real truth is the trouble caused by "little three" hiding behind it, which makes maintenance take a lot of detours. According to experience, general overhaul of multi cylinder fire failure, will first check spark plugs, injector and other problems, that is, the thought of the line, and often overlook the control line lead to the triode caused by the multi cylinder fire failure. As a maintainer, it is not simple to judge by the maintenance experience, to learn more, to truly understand the principle of electronic control engine, and to experience a solid foundation of theoretical knowledge is the hard truth.