he barometric pressure/manifold absolute pressure
(BP/MAP) sensor is critical in determining fuel mixture and spark advance under
varying loads. Much like a Throttle Position Sensor, it must provide a smooth,
gradual change in output, or drive ability problems can occur. In some instances,
a BP/MAP sensor can deviate without setting trouble codes. To verify its
operation, you need to check its output over its full operating range.
Fig 8.
Click on graphic to view larger image.
Fig 8 - Using DC-Coupled Hz to Check BP/MAP Sensors To test
the performance of a BP/MAP sensor, graph its frequency output at
various levels of vacuum. Start with the sensor at 0" Hg (0 cm /hg)
and read its frequency. Then note the frequency at each increase of
1" Hg (cm Hg). When you plot these frequencies, they should be in a
straight line. The frequency will decrease with an increase in vacuum.
