MAP Sensor off-car

As the pressure decreases inside the manifold so those the voltage output of this sensor

Manifold Absolue pressure:

This sensor compares the pressure inside the manifold with ambient pressure which is normaly 1 bar . It is either located on the manifold or on the fire wall and is connected to the intake manifold via a hose . As the silicon inside is deform between the two different pressure on either side of it ,it creates a voltage which sends back to the ECU . It normally consists of 3 pins inside the plug . 1 is power normal 5 Volts ,2 is ground , 3 is the signal back to the ECU to report back how much pressure or vacuum is inside the manifold... More pressure is less vacuum and that means more voltage output to the ECU also less pressure means more vacuum and that means less voltage output to the ECU