One. The connecting hose between the air flow meter and the throttle body is not sealed.

The vane-type air flow meter integrates the functions of the fuel pump switch, air temperature sensor and CO adjustment. Therefore, a good seal for the connection of the air flow meter and the throttle body is a necessary condition to ensure the correct calculation of the intake air volume. Once the hose is not tightly sealed or damaged, it will often cause the following failures: the engine can start the car at cold start, and the engine stalls at idling speed after warming up; after the engine is started hot, the idling speed stalls quickly; the engine starts the car, idling jitters, and stalls when in gear (automatic Transmission); the engine idling is normal (by adjusting the CO device), and the mixture is too lean when accelerating, resulting in backfire.

two. Disconnection fault of vane air flowmeter

After the vane air flowmeter is disconnected, the engine generally has a fault code, and the content is mostly the following:

Ground wire disconnection: Due to the ground wire disconnection, the output voltage of the air flow meter is kept at the highest, so the air temperature sensor is also kept at the highest output voltage, the computer fuels excessively, the CO emission exceeds the standard, and the engine emits black smoke when it is running.

Live wire disconnection: Because the power supply live wire is disconnected, the air flow meter always keeps the lowest output voltage, so the engine can run at idle speed, and the maximum idling speed is lower than 2500r/min, and acceleration is weak.

The reference voltage line is open: The output voltage of the air flow meter is too high due to the open circuit of the reference voltage line, so the engine emission CO seriously exceeds the standard.

The fuel pump switch is damaged or open circuit: the fuel pump supplies fuel when the engine is started. After starting, the fuel pump relay does not work and the engine stops.

Three. Vane type air flow meter adjustment failure

Vane air flow meters should keep the blades and slides clean. When adjusting, the CO emissions of the engine can be adjusted by adjusting the opening of the air bypass channel. When it is confirmed that there is no air leakage in the intake air and no sticking of the blades, the CO is adjusted to meet the idle exhaust emission requirements.

Kalman vortex air flowmeter failure

The Kalman vortex air flowmeter transmits the signal processed by the integrated circuit on the sensor to the computer, and the output is generally a frequency signal, so the measured output voltage is generally 2.2 ~ 2.8V. When the air flow changes, the voltage is always the same, and the output pulse frequency changes, so the flow change cannot be determined based on the measured voltage.
This kind of air flow meter should generally pay attention to the following two inspections:

(1). Check the line voltage

The power supply voltage is 4.5-5.5V; the signal voltage is 2.2-2.8V; the voltage of the air temperature sensor is 5V when the air temperature sensor is open, and the voltage is 0.1V when the air temperature sensor is short-circuited.

(2). Check the cleanliness of the air intake passage and the comb flow grille

Unclean air passages and comb flow grille will directly affect the smoothness of air flow, especially when the engine is running at high speed, these pollution will cause the air to vibrate and be recorded as a flow signal, thereby affecting the accuracy of the air flow meter.

Hot wire air flow meter failure

The measurement method of the hot-wire air flowmeter is mainly based on air quality, which is generally not affected by the intake air temperature. In addition, since it needs to be self-cleaning when it is turned on and off, the power supply voltage is generally 12V, the signal reference voltage is 5V, and the output signal voltage is 0.3 to 4.5V.
Since modern electronically controlled engine ECU has self-learning and memory functions, it can memory and correct the pollution of the air flow meter (corrected with input value feedback signal). Therefore, when testing the system, pay attention to checking the changes in the air flow data, because the air leakage and the dirty throttle will cause the air flow meter data to be inaccurate, and the fault code will often be memorized, so you cannot simply rely on the fault. Code to determine whether the air flow meter is damaged.

(1). The throttle is too dirty,

the cylinder and the valve are seriously deposited, causing the engine ECU memory air flowmeter failure and oxygen sensor failure
The reason for this is that after the throttle is too dirty, it directly affects the cross-sectional area of ​​the intake passage, thereby reducing the amount of intake air. In order to stabilize the engine idling speed, the computer can only increase the opening of the electric throttle to meet the demand for air volume under engine idling conditions. On the one hand, the computer receives the air intake signal from the air flow meter, on the other hand, it judges the accuracy of the air flow meter through the throttle opening and the engine speed. When the difference between the two calculations exceeds the preset value, it is judged that the flow meter is out of alignment. , It will be reported that the air flow meter is overvalued. When the throttle is seriously polluted, the throttle is bound to open larger, but the actual intake air volume at this time has not increased, so the signal value of the throttle position sensor will be higher than the signal value of the air flow meter. At the same time, the computer will also correct the difference of the air flowmeter, but as time goes on, when the correction value exceeds the computer’s preset value, it will report a flowmeter misalignment fault.
Therefore, the throttle body should be cleaned in time to ensure the accuracy of the air flow meter.
After the vehicle has such a failure, do not rush to replace the air flow meter. You should first clean the intake duct, throttle valve, cylinder and valve without disassembly, and then use special equipment to clear the fault memory in the computer (fault code and operating data) Record), and re-run the vehicle to make preliminary settings, the fault can generally be eliminated.

(2). Air flow meter intake comb grid failure

Many maintenance personnel generally believe that after the hot-line air flow meter has a self-cleaning function, the hot-line part is not easy to be contaminated. It should be said that this view is incorrect. The reason is that if the crankcase steam and the air filter element are too dirty, the air flow meter grille is also susceptible to contamination. Since the thermal resistance air flowmeter takes the middle part of the air for sampling calculation, it is required that the air entering the air flowmeter channel must be uniform. When the grille is too dirty, the air cannot be accurately measured due to the turbulence generated when the air flows at high speed, which causes the mixed air to be too thin when the engine is accelerating, resulting in backfire. In this case, the air flow meter grille needs to be cleaned correctly.