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 when the engine is started and when driving fully loaded, then the pressure sensor information is adjusted accordingly.
The Manifold Absolute Pressure (MAP) sensor was used on the 3.8L & the 5.0L engines, until it was replaced by the Mass Air Flow (MAF). The MAP sensor operates as a pressure-sensing disc. It does not generate a voltage; instead its output is a frequency change. The sensor changes frequency according to intake manifold vacuum; as vacuum increases sensor frequency increases. This gives the Powertrain Control Module (PCM) information on engine load. The PCM uses the MAP sensor signal to help determine spark advance, EGR flow and air/fuel ratio.
Removal & Installation
- Disconnect the negative battery cable.
- Detach the electrical connector and the vacuum line from the sensor.
- Remove the sensor mounting bolts and remove the sensor.
- Installation is the reverse of the removal procedure.
- Connect a 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.
Measure the reference signal of the MAP sensor. If the DVOM voltage reading is as indicated in the table, the sensor is okay.
- Turn the ignition OFF .
- Disconnect the vacuum hose from the MAP sensor and connect a vacuum pump in its place.
- Apply 18 in. Hg of vacuum to the MAP sensor.
- If the MAP sensor holds vacuum, it is okay. If the MAP sensor does not hold vacuum, it must be replaced.