Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor:

The Manifold Absolute Pressure (MAP) Sensor measures the changes in intake manifold pressure resulting from engine load and speed changes, converting this to an ECM voltage input signal.

A closed throttle on deceleration produces a relatively low MAP output, while wide open throttle produces a high output. This high output is produced because the pressure inside the manifold is the same as outside the manifold, resulting in a measurement of 100% of outside air pressure.

Manifold absolute pressure is the OPPOSITE of engine manifold vacuum. When manifold pressure is high, vacuum is low. The MAP sensor also measures barometric pressure under certain conditions, enabling the ECM to made adjustments for altitude changes.

The ECM sends a 5V reference signal to the MAP sensor. As manifold pressure changes, the electrical resistance of the sensor also changes, allowing the ECM to "know" manifold pressure. High pressure (low vacuum and high voltage) requires more fuel. Low pressure (high vacuum and low voltage) requires less fuel.

The ECM uses the MAP sensor input signal in its calculations for fuel delivery and ignition timing.

The MAP sensor voltage signal range is as follows:

Altitude (meters/feet) Voltage Range

Below 305 / 1,000 3.8 - 5.5V
305-610 / 1,000-2,000 3.6 - 5.3V
610-914 / 2,000-3,000 3.5 - 5.1V
914-1219 / 3,000-4,000 3.3 - 5.0V
1219-1524 / 4,000-5,000 3.2 - 4.8V
1524-1829 / 5,000-6,000 3.0 - 4.6V
1829-2133 / 6,000-7,000 2.9 - 4.5V
2133-2438 / 7,000-8,000 2.8 - 4.3V
2438-2743 / 8,000-9,000 2.6 - 4.2V
2743-3048 / 9,000-10,000 2.5 - 4.0V