The D type EFI system eliminates the use of an air flow meter and uses a manifold absolute pressure sensor as a load measurement device instead.
Because pressure in the intake manifold is proportional to the amount of air entering it, the manifold absolute pressure sensor is used to measure air intake volume in the D type EFI system.
This sensor compares a variable pressure inside the intake manifold with a fixed reference pressure inside the sensor. A total vacuum chamber is placed on one side of a piezo-resistive silicon chip; manifold pressure is applied to the other side of the chip. As the chip flexes, the mechanical movement is converted into a variable voltage signal by the sensor. There are several different names used in reference to the Manifold Absolute Pressure sensor, depending on the publication you read. Two other common names used to refer to this sensor are PIM, or Pressure Intake Manifold, and Vacuum sensor.
For more information about operation of the manifold absolute pressure sensor and its signal characteristics, refer to "Electronic Engine Controls."
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