A Mass Air Flow (MAF) Sensor is a very important component of today’s modern day electronic fuel injected (EFI) gasoline engines. The MAF Sensor is used by the engine control module (ECM) to determine the mass of air entering the combustion chamber of the engine. With the mass air flow information, engine speed (rpm) and engine load (throttle position), the ECM can accurately deliver the necessary fuel for complete and efficient combustion (i.e. more power).
A MAF does not directly measure the mass of air entering the combustion chamber, but rather accurately estimates it by taking an indirect measurement from a small sample of the air flow. This is important to note, because if something upstream of the MAF alters the flow characteristics then this will impact the output of the MAF and ultimately the fuel delivery when the ECM is operating in closed-loop. The MAF Sensor utilizes a hot wire filament that could be housed in a separate sample tube or suspended in the main flow path of the intake system. This hot wire filament is heated by passing an electrical current through the filament, but like a light bulb. When air flows across the heated filament, heat is transferred from the filament to the air through convection. As the hot wire filament changes in temperature so does its internal resistance. As the temperature of the filament decreases, the resistance of the filament will also decrease. When the filament resistance decreases, the amount of current flow through the filament will increase. So the more heat that the air flow can transfer from the filament the higher the current will be through the hot wire filament. It’s the measurement of this current that is proportional to the mass of air flowing across the filament. This current is the converted to a voltage signal that is typically on the order of 0-5volts, which is then sent to the ECM for control of the fuel delivery.
It is important to maintain your MAF sensor so that its calibration does not change. Reference the How-To section for more information on how to maintain your MAF sensor to ensure you are getting the maximum performance from you fuel inject car.