Manifold absolute pressure sensor
The pressure sensor contains a pressure-sensitive
ceramic sensing device, an amplifier and a circuit for
temperature compensation. The pressure sensor is
connected by a short special .hose to the engine in-
take manifold after the throttle and is supplied with 5
V from ECM pin 43 and grounded from ECM pin 67.
Depending on the pressure in the intake manifold,
the pressure sensor supplies a proportional voltage
to ECM pin 22.
The ECM uses pressure and temperature in the in-
take manifold to calculate the engine load, i.e. how
great an air mass each cylinder draws in. The fuel in-
jection time is proportional to the air mass drawn in.
At atmospheric pressure (100 kPa), the voltage from
the pressure sensor is approx. 1.9 V. Information
from the pressure sensor is also used to calculate
ignition timing and for boost pressure control.
If the hose comes loose or the sensor fails, and in the
event of a break in the circuit, the engine control mod-
ule will use the throttle position as a default value.
Saab9000
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Technical Description 31
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589
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