G 2500 3/4 Ton Van V8-350 5.7L VIN K TBI (1995)
Manifold Pressure/Vacuum Sensor: Description and Operation
MAP Sensor
PURPOSE
The Manifold Absolute Pressure (MAP) sensor is a pressure sensitive variable resistor. It measures the changes in the intake manifold pressure
which result from engine load and speed changes, and converts this to a voltage output. The computer uses this voltage output to control fuel
delivery and ignition timing.
OPERATION:
A closed throttle on engine coastdown would produce a relatively low MAP voltage output, while a wide open throttle would produce a high
voltage output. Manifold absolute pressure is the OPPOSITE of vacuum. When manifold pressure is high, vacuum is low. The MAP sensor is also
used to measure barometric pressure under certain conditions, which allows the control module to automatically adjust to different altitudes. The
control module sends a 5 volt reference signal to the MAP sensor. As manifold pressure changes, electrical resistance of the sensor also changes.
By monitoring the sensor output voltage, the control module knows the manifold pressure. A high pressure, low vacuum (high voltage) condition
requires more fuel, while a low pressure, high vacuum (low voltage) requires less fuel.
The control module used the MAP sensor to control fuel delivery and ignition timing.
