How to maintain automobile air flowmeter

Air flowmeter is an instrument that converts the inhaled air flow into electrical signals. The automobile air flowmeter is used to detect the air intake of the automobile engine, which converts the air intake information of the engine into an electrical signal and sends it to the ECU of the on-board computer. Automobile air flowmeter is a sensor used to measure the air intake in automobile air intake system. The engine can calculate the fuel injection quantity according to the data value of this intake air volume. Failure or damage of automobile air flow meter may lead to unstable idle speed, poor acceleration, increased fuel consumption, high speed weakness, black smoke from exhaust pipe, excessive exhaust emission and so on.

Air flow meters are divided into two types according to sensor signal types, including analog signal flow meters and digital signal flow meters.

Let's take a look at how to measure a digital signal flowmeter with an oscilloscope. Connect the channel to a line from BNC to banana head, then connect a needle to the red interface of banana head, connect a crocodile to the black interface of banana head, and then connect the needle to the signal line of the air flow meter sensor. The crocodile is clamped on the ground of the vehicle.

BMW air flowmeter sensor

Next, let's set up the oscilloscope. If your oscilloscope is the ATO series of Maxine Auto Repair, you only need to open the auto repair package software, select Sensor-Air Flow Meter-Digital, and then click OK.

For other oscilloscopes, we first set the channel to DC coupling, the probe type is voltage, the attenuation ratio of the channel is 1X, turn on the low-pass 30KHz, and set the vertical gear to about 5V, and turn on the amplitude, high value, low value and frequency in the measurement items for observation.

The time base can be set to about 1 sec or longer. When the waveform is displayed on the screen, quickly step on the accelerator and observe the waveform from idle speed to full throttle, so that we can see the movement of the air flowmeter from idle speed to acceleration and then back to idle speed on a screen. Pay special attention to the oscilloscope waveform and the measured values at the fault speed of driving ability.

Mazda 6 air flow sensor+throttle position sensor.

For the analog signal flowmeter, the vane flowmeter is described here. The vane air flowmeter is characterized by integrating the functions of fuel pump control switch, air temperature sensor, CO regulator and air flowmeter, with complex structure but high accuracy. Its working principle is to let air flow into the engine, pass through the measuring unit and flow through the blades with springs, and the movement of the blades is proportional to the amount of air entering the engine. The movement of the air knife is recorded by the sliding arm sliding on the carbon rail, and the voltage output of the sliding arm is reported to the electronic control module (ECM), and then the ECM delivers the correct fuel quantity according to the measured air flow. The wiring of this air flowmeter is usually four-wire, five-wire and seven-wire.

The connection method is similar to before:

Connect BNC- banana head cable to channel 1 of oscilloscope.

Connect the crocodile clip to the black connector of the banana head line.

Connect the needle to the red connector of the banana thread.

Connect the alligator clip to the negative battery ground.

Connect the pointer to the signal output of the air flow meter.

When the waveform is displayed on the screen, step on the accelerator and observe the waveform from idle speed to full throttle.

The auto repair package of Maxine's auto repair model ATO also supports the one-button test of the hot-wire air flowmeter sensor, which distributes the heating wires evenly in the metering channel. The sensor uses platinum wire as hot wire resistor and thermistor to detect the ambient temperature and is installed in the detection area of the air inlet. When the hot wire is electrified, it generates heat. When the airflow passes through the hot wire, the heat of the hot wire is cooled. By controlling the current on the hot wire, the temperature on the hot wire can be kept constant. In this way, the control current has a corresponding proportional relationship with the air intake, that is, the air flow can change the output voltage of the air flowmeter. The output signals of hot-wire air flow meters produced by various automobile factories are slightly different.

Hot-wire air flowmeter is made according to the principle of heat dissipation. It has the advantages of simple structure, no mechanical rotating parts, durability, high precision and accurate measurement of air volume. However, because the hot wire is very thin and exposed to the air, when the air flows at high speed, the sand in the air can easily break the hot wire.

There are two kinds of hot-wire air flowmeter: analog and digital. The difference is that the digital output is a digital signal and the analog output is a voltage signal, so the computer can be used directly without conversion. Generally, the frequency of digital air flowmeter increases with the increase of air flow.