A Mass Air Flow engine managment system uses a mass-air-flow sensor (Maf Sensor) which is placed in the intake tract to directly measure the mass of air entering the engine. With this information and the size of the injectors, the ECU is able to calculate the fuel injector pulse-width required to deliver the desired Air Fuel Ratio. MAF systems typically use tables of desired Air Fuel Ratios versus airflow.

This differs from Speed Density systems (such as those used in Honda PGM-FI systems) that use Volumetric Efficiency tables combined with sensor measurements to estimate airflow without directly measuring it.