The amount of fuelling changes with the amount of air taken into the engine. The colder the incoming air and the higher it’s pressure, the denser it is so the actual mass of air will very depending on the ambient temperature and pressure, and the effects of the turbo charger and inter cooler. Earlier vehicles and those without exhaust gas recirculation, have an intake air temperature sensor mounted in the air inlet manifold, and a manifold absolute air pressure sensor mounted near the fuel filter. These supply data to allow the ECM to calculate the amount of entering the engine. The MAP sensor is also known as the boost pressure in the manifold is directly related to the turbocharger’s boost effect. Latter and EGR engine have mass airflow sensors that contain a film, across which the incoming air passes. The ECM sends an electrical supply through the film, heating it to 200C. Incoming air tends to cool the film, and the ECM knows what the air temperature is by the amount of current it needs to send. These vehicles don’t need an IAT sensor.
on vehicle fitted with EGR the ECM uses information on engine load to signal the EGR modulator to reduce emissions.
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