Intrepid V6-3.5L VIN K (2003)
the crank position, the PCM powers up, and looks at the MAP voltage, and based upon the voltage it sees, it knows the current barometric pressure
relative to altitude. Once the engine starts, the PCM looks at the voltage again, continuously every 12 milliseconds, and compares the current voltage to
what it was at key on. The difference between current and what it was at key on is manifold vacuum.
During key On (engine not running) the sensor reads (updates) barometric pressure. A normal range can be obtained by monitoring known good sensor
in your work area.
As the altitude increases the air becomes thinner (less oxygen). If a vehicle is started and driven to a very different altitude than where it was at key On
the barometric pressure needs to be updated. Any time the PCM sees Wide Open throttle, based upon TPS angle and RPM it will update barometric
pressure in the MAP memory cell. With periodic updates, the PCM can make its calculations more effectively.
The PCM uses the MAP sensor to aid in calculating the following:
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Barometric pressure
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Engine load
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Manifold pressure
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Injector pulse-width
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Spark-advance programs
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Idle speed
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Decel fuel shutoff
The MAP sensor signal is provided from a single piezoresistive element located in the center of a diaphragm. The element and diaphragm are both made
of silicone. As the pressures changes the diaphragm moves causing the element to deflect which stresses the silicone. When silicone is exposed to stress
its resistance changes. As manifold vacuum increases, the MAP sensor input voltage decreases proportionally. The sensor also contains electronics that
condition the signal and provide temperature compensation.
The PCM recognizes a decrease in manifold pressure by monitoring a decrease in voltage from the reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; as pressure changes, voltage changes proportionately. The range of voltage output from the sensor is usually
between 4.5 volts at sea level to as low as 0.3 volts at 26 in. of Hg. Barometric pressure is the pressure exerted by the atmosphere upon an object. At sea
level on a standard day, no storm, barometric pressure is 29.92 in Hg. For every 100 feet of altitude barometric pressure drops 0.10 in. Hg. If a storm
goes through it can either add, high pressure, or decrease, low pressure, from what should be present for that altitude. You should make a habit of
knowing what the average pressure and corresponding barometric pressure is for your area. Always use the Diagnostic Test Procedures Manual for MAP
sensor testing.
