Mercury MerCruiser D2.8L D-Tronic Service Manual page 488

DESCRIPTION
Manifold Absolute Pressure (MAP) Sensor
The Manifold Absolute Pressure (MAP) sensor is a pressure transducer that measures the
changes in the intake manifold pressure. The pressure changes as a result of engine load
and speed change, and the MAP sensor converts this to a voltage output.
The ECM sends a 5 volt reference signal to the MAP sensor. As the manifold pressure
changes, the electrical resistance of the MAP sensor also changes. By monitoring the
sensor output voltage, the ECM 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 ECM uses the MAP sensor to control fuel delivery and
injection timing.
A closed throttle position on engine coast-down would produce a relatively low MAP output
voltage, while a wide open throttle would produce a high MAP output voltage. This higher
output voltage is produced because the pressure inside the manifold is increasing. When
manifold pressure is high, vacuum is low.
A failure in the MAP sensor circuit should set a Code P0105.
Page 5A-22
a
e
d
a - Sensor
b - Pressure Sensor
c - Temperature Sensor
d - Electrical Connector Attachment
e - Locking Tab
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90-860074--1 FEBRUARY 2002
SERVICE MANUAL NUMBER 22
b
c
75408