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An air flow meter is a device that converts the flow rate of the inhaled air into an electrical signal. The car air flow meter is used to measure the amount of air entering the car engine; it converts information about the engine’s air intake volume into electrical signals, which are then sent to the vehicle’s computer ECU. The car air flow meter is a sensor in the car’s intake system that measures the amount of air entering the engine. The engine can calculate the fuel injection amount based on this intake air volume value. A faulty or damaged car air flow meter can cause unstable idling, poor acceleration, increased fuel consumption, lack of power at high speeds, black smoke from the exhaust, and excessive exhaust emissions. https://pic4.zhimg.com/80/v2-3e8a2602e360de6b1b4e3b47ac86e487_720w.jpg Air flow meters can be classified into two types based on the type of sensor signal they use: analog signal flow meters and digital signal flow meters. Let’s first take a look at how to measure digital signal flow meters using an oscilloscope. Connect Channel 1 to a BNC-to-banana plug cable; then connect a probe to the red port of the banana plug, and attach a alligator clip to the black port of the banana plug. Connect the probe to the signal wire of the air flow sensor, and fasten the alligator clip to the vehicle’s ground. https://pic2.zhimg.com/80/v2-518a93cb6d14a5c1b2d0ce83c46853b5_720w.jpg BMW air flow meter sensor. Next, we will configure the oscilloscope; if your oscilloscope is from the ATO series made by Mackox for automotive repair purposes, you simply need to open the repair software, select Sensor – Air Flow Meter – Digital, and then click OK. https://pic2.zhimg.com/80/v2-24d79650455fd05ef79de756ae92c471_720w.jpg For other oscilloscopes, we first set the channel to DC coupling, use a voltage-type probe, set the channel attenuation to 1X, enable a low-pass filter at 30KHz, and set the vertical scale around 5V. Then we activate the measurement functions for amplitude, maximum value, minimum value, and frequency in order to make observations. https://pic2.zhimg.com/80/v2-7855cdfa6e10dc19fe02bb5ae9f1fc21_720w.jpg The timing can be set to about 1 second or more; when the waveform is displayed on the screen, quickly press the accelerator from idle to full throttle, and observe the waveform. This way we can see on the screen the movement of the air flow meter as it goes from idle to accelerated speed and then back to idle. Pay special attention to observing the oscilloscope waveforms and measurement values at the fault speed related to driving capability issues. https://pic2.zhimg.com/80/v2-03e09f77a396b6a9fb26e0e1b411d119_720w.jpg The Mazda 6’s air flow meter sensor and throttle position sensor – for analog-type flow meters, a vane-type flow meter is used as an example here. The characteristic of the vane-type air flow meter is that it integrates functions such as the fuel pump control switch, air temperature sensor, CO regulator, and air flow meter into one unit; its structure is relatively complex, but its accuracy is high. Its working principle is to allow air to flow into the engine; through a measuring unit, it passes over blades equipped with springs, and the movement of these blades is proportional to the amount of air entering the engine. The movement of the air vane is recorded by a slider that slides along a carbon track; the voltage output from this slider is sent to the electronic control module (ECM), which then delivers the correct amount of fuel based on the measured air flow. The common wire connections for this type of air flow meter are four-wire, five-wire, and seven-wire. https://pic2.zhimg.com/80/v2-2b3c38d107ee0826703552bd6409bcad_720w.jpg The connection method is similar to before: Connect a BNC-to-banana plug cable to channel 1 of the oscilloscope; connect a alligator clip to the black terminal of the banana plug, and another probe to the red terminal. Connect the alligator clip to the negative terminal of the battery for grounding, and use the probe to connect to the signal output terminal of the air flow meter. Once the waveform appears on the screen, press the accelerator from idle to full throttle and observe the waveform. McCossin’s ATO auto repair kit also supports one-click testing of hot-wire air flow meter sensors; a hot-wire air flow meter features a heating wire that is evenly distributed within the measurement channel. The sensor uses a platinum wire as the heating wire resistor and a thermistor to detect the ambient temperature, and is installed in the detection area of the intake duct. When current flows through the heating wire, heat is generated. As air flows past the heating wire, the heat from it is dissipated; by controlling the current flowing through the wire, its temperature can be kept constant. In this way, there is a proportional relationship between the control current and the air intake volume; that is, the airflow can change the output voltage of the air flow meter. The output signals of the hot-wire air flow meters produced by various automobile manufacturers vary slightly. https://pic1.zhimg.com/80/v2-f7713034fe74da30904978ac39829428_720w.jpg Hot-line air flow meters are designed based on the principle of heat dissipation; they have a simple structure, no mechanical moving parts, are durable, and offer high precision, enabling accurate measurement of air volume. However, since the heating wire is very thin and exposed to the air, sand particles in the air can easily break it when the air flows at high speeds. Hot-wire air flow meters come in both analog and digital versions; the difference is that digital models output digital signals while analog models output voltage signals, which can be used directly by a computer without any conversion needed. Typically, in digital air flow meters, the frequency increases as the air flow rate increases. https://pic3.zhimg.com/80/v2-72ec5208bc890c2d38cc7b5ba80339f6_720w.jpg