Understanding Mass Air Flow - Ford Muscle (blog)
However, we knew the "speed density" fuel injection system would need to be upgraded to a mass air flow system in order for the engine to respond properly to induction upgrades. Speed Density was Ford's earliest method of electronic fuel injection. Fuel injection of any type works by monitoring various sensors to determine engine load and then adjusting the amount of fuel delivered to maintain the desired air-fuel ratio. Speed density systems are called so because load is calculated by the speed of the engine (rpm) and the density of air within the intake manifold, as measured by the MAP (manifold absolute pressure) sensor. Speed density systems are accurate because the data within the control module (e. g. computer) is based around the specific engine configuration. For instance, the speed density computer in our F150 contains spark and fuel tables specific to the F150 5. 0L engine. Mass air flow (MAF) systems evolved later and are highly adaptable because they directly measure the volume of air going into the engine. The mass air flow meter mounts between the air filter and throttle body, and consists of a pair of small wires located within a calibrated housing. Source: www.fordmuscle.com
