MAP sensors

Manifold absolute pressure sensors

The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an internal combustion engine's electronic control system. They sense the pressure of air  inside the intake manifold,which is used to monitor the flow rate of air inside the manifold. The engine control unit (ECU) needs the information regarding the amount of air entering the combustion chamber in order to control the fuel supply, This can be done either using MAF (mass air flow) sensor or MAP sensor. We will talk about MAF sensors latter on. Lets discuss about MAP sensors now,

                              The red part is silicon chip

They are generally used in fuel injected engines. The manifold absolute pressure sensor  provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel supply for optimum combustion. 

Construction and working of MAP sensors

The MAP sensor contains an extruded part which is fitted inside the intake manifold. The extruded part have silicon chip fitted inside it which acts as a diaphragm. When air flows inside the intake manifold the pressure inside it decreases.The decreased pressure tries to pull the silicon chip and hence it's length increase. The increased length causes decrease in cross section area and hence it's resistance decreases. Now the pressure inside the intake manifold is calculated based on the resistance data using suitable algorithms. This pressure is used to determine the the density of air entering based on the temperature data (from temperature sensor). Now the density is used to calculate mass air flow rate of air. The ECU calculates all these data and control the amount of fuel accordingly so as to maintain the proper air fuel ratio.