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The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure, which result from the engine load and speed changes, and converts this to a voltage output. A closed throttle on engine coastdown will produce a low MAP output, while a wide-open throttle will produce a high output. This high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100 percent of the outside air pressure is measured. The MAP sensor reading is the opposite of what you would measure on a vacuum gauge. When manifold pressure is high, vacuum is low. The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the VCM to automatically adjust for different altitudes. The VCM sends a 5 volt reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the VCM knows the manifold pressure. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires less fuel. The VCM uses the MAP sensor to control fuel delivery and ignition timing.
See Figures 1, 2 and 3
Fig. 1: Typical Manifold Absolute Pressure (MAP) sensor wiring diagram (wire color, terminal identification/location may vary on certain models)
Fig. 2: Using jumper wires and a high impedance voltmeter test between MAP sensor terminals A and C with the key ON and engine off. The voltage should be approximately 5 volts Fig. 3: Next test between MAP sensor terminals A and B with the key ON and engine off. The voltage should be approximately 0.5 voltsREMOVAL & INSTALLATIONExcept 1998-99 2.2L Models
See Figures 4 through 8
Fig. 4: Manifold Absolute Pressure (MAP) sensor location-1996 4.3L engine shown, others similar Fig. 5: Manifold Absolute Pressure (MAP) sensor location-1994-97 2.2L engine Fig. 6: Unplug the Manifold Absolute Pressure (MAP) sensor electrical connection Fig. 7: Unfasten the Manifold Absolute Pressure (MAP) sensor retainers ... Fig. 8: ... then remove the MAP sensor
1998-99 2.2L Models