Manifold Pressure/Vacuum Sensor: Description and Operation

The MAP sensor measures changes in intake manifold pressure resulting from changes in engine load and speed, and converts this to a voltage output. The ECM, by monitoring sensor output voltage, increases or decreases injector ``on'' time to compensate for the addition or reduction of fuel as required.
The MAP sensor is used by the ECM to control fuel delivery and ignition timing. In addition, the sensor is also used to measure barometric pressure under certain conditions, allowing the ECM to automatically adjust for different altitudes.