In electronically controlled gasoline injection engines, the oxygen sensor used for closed-loop control of the fuel system is an important electronic component used to monitor the oxygen content of the exhaust gas and is fed back to the ECU with a voltage signal to control the air-fuel ratio to remain at 14.7. At the same time, it is the endorsement alarm component of a variety of fault signals.
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First, the fault diagnosis of oxygen sensor
According to the characteristic curve of the zirconia sensor, when the air-fuel ratio is maintained at 14.7, the signal reference voltage is 0.4-0.5V, and when the air-fuel ratio is less than 14.7, the voltage is gradually increased to 0.8-lV, indicating that the mixture is too rich. When the air-fuel ratio is greater than 14.7, the voltage gradually drops to about 0.2V, indicating that the mixture is too lean. This is an important basis for the diagnosis of oxygen sensors. The diagnostic method is:
1. Run the engine at 2500r/min for 2min, preheat the sensor, unplug the sensor cable (the sensor with the heating wire is careful to insert the position), measure the feedback voltage with a multimeter, and check the number of swings of the voltmeter pointer in 10S. If it is less than 8 times, preheat the sensor again and check the number of pointer swings in 10S. If it is swung 8 times or more, it is normal. If it is still less than 8 times, proceed as follows:
2. Disconnect the sensor harness connector and measure the feedback voltage.
1) When it is greater than 0.45V, disconnect the vacuum tube somewhere on the intake pipe. If the voltage is still greater than 0.45V, the sensor is damaged. If the kid is 0.45V, the mixture is too rich, and the fuel, intake or control system should be checked.
2) When the temperature is less than 0.45V, unplug the water temperature sensor and connect a 4-8KΩ resistor. If the voltage is still less than 0.45V, the sensor is damaged. If it is higher than 0.45V, the mixture is too thin.
A common zirconia sensor failure is that the surface is covered with lead or carbide, causing the gas to be impermeable and the oxygen ions not to diffuse and fail. When the fault light alarms and the sensor is read, it is necessary to diagnose it because the oxygen sensor alarm does not necessarily mean that the sensor is faulty, and its alarm signal is also affected by the following factors.
1. The working condition of the ignition system;
2. Inlet system sealing performance;
3. Whether the exhaust system is blocked;
4. The working condition of the injector;
5. The oil pressure of the oil supply system is high or low.
Therefore, in the engine maintenance, once the oxygen sensor alarm signal appears, the computer should be added to the human brain to comprehensively analyze, judge, exchange and replace the faulty parts, and make reasonable maintenance.
Second, the ignition system working condition detection
Regular inspection of the distributor or distributorless ignition system controlled by the microcomputer. The inspection items are spark energy, spark plug, high voltage line, ignition timing, ignition advance angle, and the like. When the ignition advance timing is used to check the ignition advance angle, the red fish is clamped to the positive pole of the battery, the blackfish is clamped to the negative pole of the battery, the high pressure sensor is clamped to the high voltage line of the cylinder, and the timing light is aligned with the ignition timing mark of the front pulley of the engine. When the engine speed When rising, the ignition advance angle should increase. When the hammer sensor or the wrench is used to hit the knock sensor fixing screw or the cylinder head, the ignition advance angle should be significantly delayed.
Third, the intake system sealing performance check
Connect a vacuum gauge to the appropriate part of the intake pipe. When the engine is idling (5OO-600r/min), the sea level shall be taken as the reference. The vacuum of the intake pipe shall be in the range of 57.33-70.66Kpa. Otherwise, the air intake system shall be repaired. Part. At idle, the vacuum gauge hand gradually drops to zero, indicating that the exhaust system is blocked. The change in the vacuum gauge pointer can also detect valve seal and ignition performance.
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