Manifold Absolute Pressure Sensor
Almost all engine control systems that do not use an air mass sensor are equipped with an intake manifold absolute pressure sensor.
In such systems, based on the data on the pressure and air temperature in the intake manifold, the engine control unit calculates the mass of air contained in each centimeter of the cubic volume of the intake manifold. With each intake stroke, the cylinder "sucks" rarefied air from the intake manifold, the volume of which is approximately equal to the internal volume of the engine's cylinder. Knowing the internal volume of the engine cylinder (in cm3) and having previously calculated the density of the air drawn in by the cylinder (in g/cm3), the engine control unit calculates the mass of air (in grams) entering the cylinder during the intake stroke. In accordance with the calculated mass of air consumed by the engine, the engine control unit generates fuel injector control pulses of the appropriate duration, achieving the preparation of an air-fuel mixture with a composition close to the specified one.