Santana Zhijun speeds up and slows down.

Inspection and analysis: the maintenance personnel test run to verify the existence of the above-mentioned fault phenomena, and connect the public special diagnostic instrument to detect the electronic control system, but there is no fault code. After further inquiry, the user learned that although the car traveled 6.5438+10,000 kilometers, there was no traffic accident and no other maintenance, so there should be no complicated fault points.

Considering the phenomenon of unstable idle speed, the maintenance personnel first cleaned the throttle body and idle speed control valve and replaced the air filter. Check the ignition system, there is no leakage in the high-voltage line, the burning color of the spark plug is normal, and there is no sign of leakage in the skirt. The measured fuel pressure is 295~360 kPa, which is also normal. Measure the working voltage of oxygen sensor with multimeter. When the engine speed is 2 350 r/min, the output voltage is 0.10 ~ 0.20 V. With the increase of engine speed, the voltage keeps changing around 0.45V, which indicates that the oxygen sensor is normal. The intake data is only 1.65 g/s, which should be 2.00 ~ 4.00 g/s under normal circumstances, so it is suspected that there is air leakage in the intake system, but it is confirmed that there is no air leakage in the intake system after inspection.

Considering that the problem of the air flow meter will affect the air-fuel ratio, the plug of the air flow meter is unplugged for testing. At this time, the engine control unit enters the protection mode, and the intake air quantity will be calculated by the throttle position sensor and the engine speed signal. Sure enough, the idle speed and acceleration of the engine have improved, so the fault of the air flowmeter can be judged.

Use a multimeter to further measure the voltage between the No.2 terminal (signal output) and No.4 terminal (ground) of the air flowmeter. When idling, it is only 0.30 ~ 0.40 V, while the normal vehicle should be 0.80 ~ 1.60 V, and it is only 1.50 ~ 2.00 V (normally 3.00 ~ 4.30 V) when accelerating rapidly. Finally, the air flow meter was removed for inspection, and it was found that the internal metal hot film element was too dirty (Figure 1).

Troubleshooting: Clean the hot film components inside the air flow meter with cleaning agent, read the data stream again after reassembly, and the air flow data at idle speed and acceleration return to normal, so troubleshooting.

Review and summary: Upon inquiry, the user learned that the fault of the vehicle was caused by inadequate daily maintenance and long replacement period of air filter, which led to the dirty metal hot film components inside the sensor. Like this kind of fault, the air flowmeter still has a signal output, and it does not exceed the allowable range of working value, so it often does not record the fault code. At this time, the maintenance personnel need to combine the data flow to analyze the fault point.