Seville V8-273 4.5L (1989)
Manifold Pressure/Vacuum Sensor: Description and Operation
Manifold Absolute Pressure Sensor
The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure which results from engine load and speed changes. The
sensor converts a pressure input to a voltage output. The MAP sensor output voltage signal is directly related to pressure (kPa). A high pressure
(atmospheric pressure) will produce an output of about 4.5 to 5.0 volts. A low pressure will produce about 0.5 to 0.9 volts. Manifold absolute pressure
is the opposite of what you would measure with a vacuum gauge. When manifold pressure is high, vacuum is low.
The MAP sensor is also used to calculate barometric pressure under certain vehicle conditions. This eliminates the need for a separate Barometric
(BARO) sensor. As the manifold pressure changes, the electrical output of the sensor also changes. A higher pressure (low vacuum) requires more fuel,
while a lower pressure (higher vacuum) requires less fuel. By monitoring the sensor output voltage, the ECM can calculate the manifold pressure, and
increase or decrease the injector duration to allow for the addition or reduction of fuel. The ECM also uses the MAP sensor to control ignition timing.
A failure in the MAP sensor circuit should set a code E041, E032, or E034.
