<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2009) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> A mass (air) flow sensor (MAF) is used to find out the mass flow rate of air entering a fuel - injected internal combustion engine . </P> <P> The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine . Air changes its density as it expands and contracts with temperature and pressure . In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder . (See stoichiometry and ideal gas law .) </P>

What is the purpose of mass air flow sensor