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Working principle of air flow sensor

2019-12-28
Air flow sensor, also known as air flowmeter, is one of the important sensors of EFI engine. It converts the intake air flow into an electrical signal and sends it to the electronic control unit (ECU). As one of the basic signals to determine the fuel injection, it is a sensor to measure the intake air flow of the engine.

In order to obtain the best concentration of the mixture under various operating conditions, the air volume inhaled into the engine at each instant must be measured correctly as the main basis for ECU to calculate (control) the injection volume. If the air flow sensor or circuit fails and the ECU does not get the correct intake signal, it will not be able to control the injection quantity normally, which will cause the mixture to be too rich or too thin and make the engine run abnormally. There are many types of air flow sensors in electronic control gasoline injection system. According to their structural types, common air flow sensors can be divided into blade (wing plate) type, measuring core type, hot wire type, hot film type, Carmen scroll type, etc.

Working principle of air flow sensor

Function of air flow sensor
The air flow sensor is an important part of the engine control system. Its main function is to measure the air quality entering the engine and adjust the fuel ration based on it. In order to achieve an ideal air-fuel ratio and save fuel on the basis of ensuring the normal operation of the engine. Compared with the carburetor venturi, the air flow meter is more precise and responsive.

1. Measure the resistance value

First, turn off the ignition switch and disconnect the power cord of the battery, then remove the wire connector of the vane type air flow meter, and measure the resistance between each terminal with a multimeter. The resistance value should meet the standard value (ambient temperature is room temperature), otherwise, the air flow meter is damaged and should be replaced. Note: the data in the table is under normal temperature. When the air inlet temperature changes, the resistance between tha terminal and E2 terminal will also change.

2. Measure the voltage value

First, plug in the inlet connector of the air flow meter, then turn the ignition switch to "on" position, and use the multimeter to measure the voltage between VC terminal and E2 terminal, vs terminal and E2 terminal. The measurement results shall meet the standard values listed in Table 2. Otherwise, the air flow meter is damaged and shall be replaced.

3. Measure the working output signal

Unplug the fuel injector harness, start the engine or use the starter alone to drive the engine to rotate. Use a multimeter to measure the voltage between the vs terminal and the E2 terminal. The voltage should gradually decrease with the increasing of the blade opening. Otherwise, the air flowmeter is damaged and should be replaced.

Maintenance of Carmen vortex air flowmeter

1. Measure the resistance value

First switch off the ignition and disconnect the battery power cord, then remove the wiring connector of the air flow meter. Use a multimeter to measure the resistance between the tha terminal and E2 terminal of the air flow meter. The measured value shall conform to the standard value listed in Table 3. Otherwise, the air flow meter is damaged and shall be replaced.

2. Measure the voltage value

First plug in the inlet connector of the air flow meter, then turn the ignition switch to the "on" position, and use the multimeter to test the voltage value between the terminals listed in Table 4, which should meet the requirements of the standard value in Table 4, otherwise it means that the air flow meter is damaged and should be replaced.

3. Measure the working output signal

Unplug the fuel injector harness, start the engine or drive the engine to rotate with the starter alone, measure the pulse between E1 terminal and KS terminal with an oscilloscope, and have the pulse waveform as shown in Figure 3. Otherwise, the air flow meter is damaged and should be replaced.

Maintenance of hot wire air flowmeter

1. Turn the ignition switch to the "on" position, and use a multimeter to measure the voltage between ports 2 and 3 of the air flow meter as shown in Figure 4. The measured value should be about 5V. Measure the grounding voltage of terminal 4, which should be about 12V, otherwise measure the battery voltage or check the ECU and circuit.

2. Start the engine and keep the air inlet of the air flow meter in a static and windless state. Measure the voltage value between terminal 3 and terminal 1 of the air flow meter with the multimeter voltage block. The voltage value should be about 1.2-1.8v at idle speed. If the speed increases gradually, the voltage value will also increase gradually. When the engine speed is 2500r / min, the multimeter voltage value should be about 1.6-2.2v, no The air flow meter is damaged and should be replaced.

3. After the first two steps of detection, sometimes although the voltage value between each terminal is normal, the engine still can not accelerate or can not get on the vehicle, at this time, the air filter should be removed, and the air flow meter should be cooled from the air inlet. The voltage value between terminal 3 and terminal 1 should increase with the increase of wind speed, otherwise, the flowmeter is damaged and should be replaced.

Detection of hot film air flowmeter

1. Turn off the ignition switch, unplug the air flow meter inlet connector, and measure the resistance between terminal 3 and the body ground point with the multimeter resistance block, which should be 0 Ω.

2. Turn the ignition switch to the "on" position, and use a multimeter to measure the voltage between terminals 2 and 3 of the air flow meter, which should be the battery voltage. If there is no voltage or the reading deviation is too large, check the circuit. Check that the voltage between terminals 4 and 3 should be about 5V, otherwise, it means the ECU to air flow
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