Manifold Pressure/Vacuum Sensor: Description and Operation

PURPOSE
The manifold absolute pressure sensor reads intake manifold pressure changes with reference to zero or absolute vacuum. This measurement, referred to as manifold absolute pressure (MAP), provides the IGNITION ECM and EFI ECM with engine load information.

OPERATION
Manifold vacuum is routed to the MAP sensor via a hose from rear of right intake manifold. The MAP sensor aneroid capsule expands and contracts as absolute pressure varies. Capsule movement is converted to an electrical signal interpreted by the IGNITION ECM and EFI ECM as engine load and factored into calculations for ignition timing and fuel injection .

MAP is the OPPOSITE of engine intake manifold vacuum. When manifold pressure is high, vacuum is low. A closed throttle on deceleration creates low manifold pressure and high vacuum. At wide open throttle, vacuum is low and manifold pressure is high, approaching outside atmospheric pressure.

Ignition ECU:

LOCATION
Incorporated into IGNITION ECM and EFI ECM.