Manifold Absolute Pressure (M.A.P) Sensors

MAP sensors are very similar to MAF sensors.
It monitors vacuum pressure in the intake manifold according to engine load, and the ECU uses the data it collects to adjust ignition timing and fuel enrichment.

When the throttle is wide open (like when accelerating), the pressure in the intake manifold is at atmospheric pressure, or Lambda 1. So there is no pressure. The ECU will then give a rich fuel mixture to help combust more air. Likewise when the throttle is closed (like when the engine is idling), there will be more pressure in the intake manifold, so the ECU will respond with a leaner fuel mixture.


Wire up a MAP sensor with a 5v feed and earth. Measure the return voltage from the third wire. Using a miti-vac apply vacuum to the MAP sensor. Plot the voltage return in relation to the vacuum applied.



The voltage on this MAP sensor is high when the pressure is high in the manifold. It decreases as the vacuum pressure is dispursed. This indicates that the MAP sensor is working fine.