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How they work
Air volume measurement using a Manifold Absolute Pressure (MAP) Sensor is based on the principle that “intake manifold pressure is almost proportionate to the intake air volume of one stroke of the engine".
The MAP sensor detects the intake manifold pressure downstream from the throttle valve in order to indirectly calculate the intake air volume based on the relationship between pressure and engine rotational speed.
The MAP sensor is a compact semiconductor vacuum sensor that utilizes characteristics (piezoelectric resistance effect) whereby electrical resistance changes when pressure is applied to silicon (single crystal). Thus, the MAP sensor inputs intake manifold pressure to the engine ECU in the form of electric signals.The intake air volume is then calculated from these electric signals for accurate air-fuel ratio control.
Depending on the application, it can be used for other purposes such as measuring the boost pressure (upstream from the throttle valve) or the turbo manifold pressure in real time with high reliability even in a severe turbocharging or supercharging environment. Also temperature detection is possible in cases where there is an integrated air temperature sensor.