Car ECU maintenance knowledge[汽车维修知识]

1. Failure phenomenon
1. The fuel pressure test is 2.4～2.6kgf/cm2 (1kgf/cm2=98.1kPa), which is normal.Check on the enginesensor, Actuator and computerWire harnessAnd connectors, etc., no corrosion, breakage, short circuit, etc.
2. Connect the middle "TE1" and "E1" pins of the diagnostic socket with a jumper, openIgnition Switch, Read the fault code as No. 14.
3. CheckIgnition coilsPrimary coilresistanceThe value is 0.45Ω, and the resistance value of the secondary coil is 12.3kΩ, which meets the specified value.UnplugDistributorFor the plug, measure the resistance between G1 and G-coil as 161Ω, the resistance between G2 and G-coil as 161Ω, and the resistance between NE and G-coil as 210Ω. The gap between the signal rotor of the distributor and the protruding part of the induction coil is in compliance with the specified value.
4. When starting the engine, use an oscilloscope to check the ignition control signal line of the ignition amplifier IGT, and no pulse signal is output to the igniter.
2. Check ECU
After the above inspection and diagnosis, it is decided to dismantle and inspect the engine ECU. The engine ECU has upper and lower circuit panels.First illuminate with light to check that the solder joints on the two circuit boards are not desoldered, but it is still found that there is an electrolysis on the lower circuit board.capacitanceThe device is bursting and cracking. This electrolytic capacitor is C309 (35V15uf), and the dielectric flowing out of the capacitor is stuck on both pins. After careful inspection, it was found that C109 (10V200uf) and C107 (10V100uf) were somewhat swollen, so they were replaced. Pay attention to the positive and negative polarity of the electrolytic capacitor when welding, and the welding should be as fast as possible to avoid overheating and damaging the capacitor. Because there are densely packed copper foil wires and electronic components next to the solder joints of the electrolytic capacitor pins, the excess solder at the solder joints should be removed in time after the soldering is completed to avoid short circuits caused by the excess solder.
At the same time, it was also found that the dielectric liquid bursting out of the electrolytic capacitor C309 (35V15uf) corroded the printed circuit board and caused the copper foil line to open. After cleaning the corroded part of the circuit board with absolute alcohol, scrape the surface of the copper foil wire with a small blade, and then use a small copper wire (after tinning) to solder the copper foil wire.
Start the engine, the engine runs smoothly, all working conditions are normal, there is no fault code, and the fault is eliminated.
Three, the characteristics of electrolytic capacitors
Electrolytic capacitors are components with a certain life span.Electrolytic capacitor contains electrolyte, whencarWhen working in harsh environments, it is necessary to withstand the impact of large disparity in high and low temperatures from -40 to 80 ℃, the impact and vibration test of the quality of the road surface, and to adapt to the disparity in humidity changes and the dense circuit. Strong electromagnetic interference environment. When the electrolyte of the capacitor flows out and dries up, its capacitance is also greatly reduced, causing greater differences in circuit parameters and destroying the original balance and operating functions of the computer.
Electrolytic capacitors are prone to chronic electrolyte leakage. In the actual maintenance process, a large number of practices have proved that electrolytic capacitors will produce electrolyte seepage on the printed circuit board, and the electrolyte is a corrosive liquid, which will cause the copper foil circuit or components in a very small area. Short, open circuit.
Abnormal electrolytic capacitors may cause external symptoms. In most cases, changes in the performance and capacity of the electrolytic capacitor will cause the engine to become very unreliable, especially easy to cause idling jitter, inexplicable flameout and other faults. At this time, you can check visually, if the capacitor is swollen, bulging, there is a trace of liquid under the capacitor, or the color of the corresponding printed circuit board is slightly changed, etc., you should be alert at this time, and the capacitor may have been damaged.
Direct replacement of the suspected electrolytic capacitor is a simple repair method. On the printed circuit board, when the circuit components are dense, it is difficult to directly detect the capacitor using the on-circuit method. To this end, maintenance personnel must have relevant knowledge of computers, electronic circuits and electronic components, as well as superb welding skills. It is usually recommended to weld the suspected electrolytic capacitor directly, and then directly replace it with a capacitor of the same model.Generally, it is very cheap to buy electrolytic capacitors in electronics stores, but you should pay attention to buying high-quality electrolytic capacitors such as tantalum and niobium, and require high-precision capacitors
car repairMaintenance

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