Manifold Pressure/Vacuum Sensor: Description and Operation

PURPOSE
The manifold absolute pressure (MAP) sensor measures intake manifold vacuum. The engine control module (ECM) uses this information to determine engine load.

CONSTRUCTION
The sensor contains a silicon diaphragm covering a small vacuum port. When vacuum is applied, the diaphragm flexes which causes a low voltage signal to be generated. An internal circuit amplifies the signal to produce a higher voltage back to the ECM.

OPERATION



By a built-in sensor unit, the manifold absolute pressure sensor detects the intake manifold pressure as a voltage. The ECM then determines the basic injection duration and basic ignition advance angle based on this voltage.
Since the manifold absolute pressure sensor does not use the atmospheric pressure as a criterion, but senses the absolute pressure inside the intake manifold (the pressure in proportion to the preset absolute vacuum 0), it is not influenced by fluctuations in the atmospheric pressure due to high altitude and other factors. This permits it to control the air fuel ratio at the proper level under all conditions.