See Figures 1 and 2
The engine computer (PCM, ECU or SBEC) supplies 5 volts to the Manifold Absolute Pressure (MAP) sensor. The MAP sensor converts what it reads as the amount of intake manifold pressure into a return signal. The engine computer monitors the MAP sensor output voltage. As vacuum increases in the intake manifold, the MAP sensor voltage decreases proportionately. Also, as vacuum decreases, the MAP sensor voltage increases proportionately.
During engine cranking, before the engine starts running, the engine computer determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the engine computer determines the intake manifold pressure from the MAP sensor voltage.
Based on MAP sensor voltage and inputs from other sensors, the engine computer adjusts spark advance and the air/fuel mixture.
On the non-Premier or Monaco 3.0L engines, the MAP sensor mounts on a bracket attached to the generator bracket. The sensor is connected to the throttle body with a vacuum hose and to the PCM electrically.
On the 3.3L and 3.8L engines, the sensor mounts to the side of the intake manifold, below the positive crankcase ventilation (PCV) valve. The sensor connects electrically to the PCM.
On all Premier and Monaco vehicles the sensor is mounted in the engine compartment on the firewall. It is connected to the throttle body with a vacuum hose and to the ECU electrically.
Except Premier and Monaco
This test should be performed with the engine cold (room temperature).
- Backprobe the dark green/red tracer wire from the MAP sensor connector with a voltmeter (do not unplug the MAP connector).