Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the mass of air above the measurement point. Low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass, so that pressure decreases with increasing altitude or elevation.
The manifold absolute pressure sensor or the Map sensor is one of the sensors used in an internal combustion engine's electronic control system. The manifold absolute pressure sensor provides instantaneous manifold pressure information control ecu The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion
That basically means that the map sensor tunes the engine on the fly for optimum performance given the set conditions. If you had a carburetor the lower you were in elevation the the leaner you would want to make the mixture. The higher you go the richer you want to make the mixture due to the oxygen in the air.
2008 F-350 CCLB all stock for now... Deleting and tuning with Vivian's looney street soon.