Breeze L4-24L VIN X (2000) MAP Sensor Specs - Page 2401
Manifold Absolute Pressure (MAP) Sensor: Description and Operation
IAT Sensor And MAP Sensor
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR - PCM INPUT
The MAP sensor mounts to the intake manifold.
The MAP serves as a PCM input, using a silicon based sensing unit, to provide data on the manifold vacuum that draws the air/fuel mixture into
the combustion chamber. The PCM requires this information to determine injector pulse width and spark advance. When MAP equals Barometric
pressure, the pulse width will be at maximum.
Also like the cam and crank sensors, a 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold
pressure. The zero pressure reading is 0.5 volts and full scale is 4.5 volts. For a pressure swing of 0 - 15 psi the voltage changes 4.0 volts. The
sensor is supplied a regulated 4.8 - 5.1 volts to operate the sensor. Like the cam and crank sensors ground is provided through the sensor return
circuit.
The MAP sensor input is the number one contributor to pulse width. The most important function of the MAP sensor is to determine barometric
pressure. The PCM needs to know if the vehicle is at sea level or if it is in Denver at 5000 feet above sea level, because the air density changes
with altitude. It will also help to correct for varying weather conditions. If a hurricane was coming through the pressure would be very, very low or
there could be a real fair weather, high pressure area. This is important because as air pressure changes the barometric pressure changes.
Barometric pressure and altitude have a direct inverse correlation, as altitude goes up barometric goes down. The first thing that happens as the
key is rolled on, before reaching the crank position, the PCM powers up, comes around 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 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 CCD bus)
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Idle speed
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Decel fuel shutoff
