map sensors

[dayyoung]

what do map sensors work ?

[chas2008]

i assume you are talking about motor vehicles ?

http://www.picoauto.com/tutorials/emissions-co mponents-actuators.html

MAP Sensor (Digital)
A digital MAP sensor produces a square wave signal to the engine management ECM; this square wave changes frequency with varying engine vacuum readings. This output waveform can also be monitored on an oscilloscope, or the frequency measured on a certain multimeters that have the appropriate setting (Hz). The frequency seen at idle should match the frequency seen in the manufacturer's data. Air leaks also affect this digital form of monitoring the engine's vacuum.

With both forms of MAP sensor, the engine's fuelling will increase if the exhaust system has a restriction that impedes the flow of the spent gases.