Voyager V6-3.3L VIN 3 Flex Fuel (2003)
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 you 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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Shift-point strategies (F4AC1 transmissions only, via the PCI bus)
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Idle speed
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Decel fuel shutoff
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 4.6 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 .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.
