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Various Types of Mass Air Flow Meters / Sensors / MAFs

As your vehicle continues delivering miles of faithful service, a mass air flow sensor may be on your short list of replacement car parts to purchase at some point. These sensors are critical to the operation of the engine, allowing for the proper adjustment of the engine’s air-fuel mixture. Before you consider replacing your mass air flow sensor, it’s always a good idea to learn about the different designs of sensors that are available for most vehicles.

VAF and MAF Mass Air Flow Sensors

The average mass air flow sensor comes in different forms, but the two most commonly used are vane meter (VAF) sensors and hot wire (MAF) sensors. VAF sensors utilize a potentiometer attached to a spring loaded flat that directs air flow. The vane moves in proportion to the air flow, consequently generating voltage in proportion to the distance it moves. In many cases, the vane’s movement directly regulates the amount of fuel injected into the cylinders. The air-fuel mixture is governed by an adjustment screw located on the side of the VAF sensor.

VAF sensors are relatively efficient and reliable, but they also have their drawbacks. For starters, VAF sensors have to be mounted in a suitable location and oriented with respect to gravity, otherwise the device will not function as intended. The electrical or mechanical contacts use with the VAF can also wear out over time. Finally, the design of the VAF sensor restricts the amount of air flow that can pass into the intake, subsequently limiting the total engine output.

Hot wire or MAF sensors use a different approach to determining the mass of air being directed into the intake. In this approach, a wire is suspended in the engine’s airstream and charged with an electrical current. As a wire heats up, its electrical resistance increases, thereby limiting the amount of electrical current that flows into the circuit the wire is attached to. As air moves over the wire, the wire cools down and causes its electrical resistance to decrease. This allows additional current to flow through circuit, which heats up the wire again until the resistance reaches equilibrium. The electronic circuit attached to the wire translates these measurements into a signal sent to the engine control unit (ECU).

The MAF sensor was first used on vehicles produced by General Motors and it affords a more compact design in comparison to the VAF. Another advantage is that it provides greater durability due to the lack of moving parts as well as an increased total engine output due to the low air flow restriction. However, the exposed wire can become contaminated with dirt and oil, causing inaccurate readings and a deterioration of the sensor itself.

Other Mass Air Flow Sensors

In addition to the common VAF and MAF sensors, there are also other types of mass air flow sensors currently in use. For example, certain engines used by General Motors employ a “coldwire” MAF sensor where sensor readings rely on inductance and oscillation frequency changes. The sensors also use a mesh that smooth out air flow to ensure a steady reading for the sensor.

Some vehicles, particularly European and Asian imports, use a KKrmmn vortex sensor to measure air flow. A perpendicular bow is used to disrupt the airstream, resulting in an oscillatory pattern of KKrmmn vortices. These vortices are then measured as they collide with a mirror, an action that interrupts a reflected light beam used to generate the pulses in response to the vortices. The vortices can also be read directly as a pressure pulse against a sensor.

As technology changes, so does the technology behind the average mass air flow sensor. Membrane sensors are the latest type of mass air flow sensors to be introduced into automobiles. In this application, a thin electronic membrane with two thin film temperature sensors is place in the airstream. One sensor measures upstream air flow while the other measures downstream air flow. A heater lies in the center of the membrane, allowing the sensors to behave similarly to a traditional MAF sensor. The membrane sensor measures the temperature difference between the two sensors and relays that information to the ECU.

As mentioned before, the mass air flow sensor plays an important role in the engine’s performance and overall operation. In most cases, changing out this sensor is a relatively straightforward task. Avid do-it-yourselfers who want to take a crack at replacing their mass air flow sensor can turn to for tips on how to perform this task, as well as other tips on various aspects of automotive maintenance.

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