What Is A MAP Sensor & What Does A MAP Sensor Do? - 1A Auto

What Manifold Absolute (MAP) Sensors Are, What They Do, and Basic Terms

• MAP is an acronym for Manifold Absolute Pressure. MAP sensors measure the air pressure in your intake manifold, which helps the engine's computer determine air / fuel ratios. MAP sensors are set to "zero" from the factory. With the car off and the key on, the MAP sensor will read "zero" at sea level.
• There is 14.7 Pounds per Square Inch (psi) on us at all times at sea level.
• "Bar" is a measurement of pressure. 1 Bar = 1.01352932 atmospheric pressure, which is 14.7 psi. (We'll say 1 Bar for simplification)
• The absence of pressure is measured in "Inches Of Mercury" (abbreviated as in. Hg).
• -1 Bar = -29.4 in. Hg
• 1 Bar = 29.4 in. Hg
• Naturally Aspirated = without a turbocharger or supercharger. Also known as "N/A".
• Forced Induction = with a turbo or supercharger
• In forced induction applications "Boost" is automotive slang for psi
• Stoichiometric Air Fuel Ratio = The ratio of the exact amount of air it takes to burn a fuel completely.
• Stoichiometric for Gasoline Engines = 14.7 : 1 (14.7 parts air to 1 part fuel).

How MAP Sensors Work

With an N/A engine running, the MAP sensor may see readings anywhere from -29.4 in. Hg to 0 psi depending on how hard you smash the pedal. The more you hit the throttle, the closer to 0 psi the MAP sensor will read, because there is less vacuum in the intake manifold. On an engine with forced induction, the MAP sensor will also measure boost.

When MAP sensor data is combined with an air temperature sensor and a known engine speed, the engine's computer (ECU) can accurately calculate the air flow rate of the engine, which then means it can calculate fuel. It does this with fuel maps that are programmed into the ECU. The fuel map guides the engine to its happy stoichiometric place.