Ford Pick-Ups/Expedition/Navigator 1997-2000

Manifold Air Pressure Sensor



The most important information for measuring engine fuel requirements comes from the pressure sensor. Using the pressure and temperature data, the PCM calculates the intake air mass. It is connected to the engine intake manifold through a hose and takes readings of the absolute pressure. A piezoelectric crystal changes a voltage input to a frequency output which reflects the pressure in the intake manifold.

Atmospheric pressure is measured both when the engine is started and when driving fully loaded, then the pressure sensor information is adjusted accordingly.


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Fig. Fig. 1 MAP sensor test schematic

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Fig. Fig. 2 MAP sensor altitude/voltage output relationship

  1. Connect MAP/BARO tester to the sensor connector and sensor harness connector. With ignition ON and engine OFF , use DVOM to measure voltage across tester terminals. If the tester's 4-6V indicator is ON, the reference voltage input to the sensor is okay.
  3. Measure the reference signal of the MAP sensor. If the DVOM voltage reading is as indicated in the table, the sensor is okay.


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Fig. Fig. 3 Typical MAP sensor mounting

  1. Disconnect the negative battery cable.
  3. Disengage the electrical connector and the vacuum line from the sensor.
  5. Unfasten the sensor mounting bolts and remove the sensor.

To install:

  1. Installation is the reverse of removal.