Manifold Pressure/Vacuum Sensor: Description and Operation

Digifant ECU:

The Manifold Absolute Pressure Sensor, (MAP sensor) is located inside the Digifant control unit, which is mounted at the rear of the engine compartment. The MAP sensor is used to measure intake manifold pressure. This measurement informs the ECU of engine load and manifold (boost) pressure. The vacuum hose to the MAP sensor must be exactly 1 meter (39 inches) long. The length and wall thickness of the hose is critical, if either is incorrect poor engine performance may result.

Manifold Pressure Sensor:

The MAP sensor consists of a crystal chip and two semi-conductors. The crystal is shaped in such a way that, when mounted to a base plate, it traps a small amount of air between the base plate and the chip.

The air under the chip allows the chip to flex when pressure is applied. The two semi-conductors attached to the top of the chip sense the flex of the chip. The flexing of the chip causes the semi-conductors to alter their shape. This changes the resistance values of the semi-conductors. The change or resistance values is used by the ECU to determine the amount of manifold pressure.