Cherokee 2WD L4-150 2.5L VIN H TBI (1988)
Manifold Pressure/Vacuum Sensor: Description and Operation
MAP Sensor Description
The MAP sensor senses engine load. It sends voltage signals to the ECU that represent the engines varying load conditions. The MAP sensor is
connected to a manifold vacuum source via a vacuum hose. These changes in manifold absolute pressure are determined by driver demand (amount of
throttle). Changes in manifold absolute pressure are sensed by a silicon crystal, via the vacuum hose, in the MAP sensor. This crystal changes the
resistance of the sensor depending upon the manifold absolute pressure acting upon it, and the change in resistance affects the amount of voltage that the
sensor allows to flow back to the ECU. The ECU uses this information and other input signals to make decisions as to what output devices need to be
adjusted to improve the driving conditions or emission levels.
The relationship between the resistance of the MAP sensor and the manifold absolute pressure is inversely proportional (As the manifold absolute
pressure increases, low vacuum, the resistance of the sensor decreases and vice versa). The relationship between the manifold absolute pressure of the
MAP sensor and the voltage returned to the ECU is directly proportional (As the manifold absolute pressure increases, low vacuum, the voltage returned
to the ECU increases and vice versa).
The voltage supplied to the MAP sensor from the ECU is 5 volts, and its voltage range is .5 to 5 volts. .5 to 1.5 volts indicates a high vacuum situation
such as idle or deceleration. 1.5 to 3.0 volts indicates a medium level of vacuum such as a cruise or slight acceleration condition. 3.0 to 4.5 volts
indicates a low vacuum situation such as hard acceleration or a mechanical failure. Any reading of 0 volts or over 5 volts indicates a problem. Refer to
specification chart in ELECTRICAL SPECIFICATIONS.
