MAP Sensors: What They Are And What They Do.

Remember science class when the teacher shouted “Pay attention! You might need this someday!” ?  Well, as much as I don’t want to admit it, that teacher was right.  Lets touch upon the basics and see if it rings a bell?

The Basics:

  • First off – 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. So with the car off, and the key on, the MAP sensor will read “zero” at sea level.
  • On earth, we have 14.7 Pounds per Square Inch (PSI) on us at all times at sea level.
  • “Bar” is a measurement of pressure.  1 Bar = 1 atmospheric pressure, which is 14.7 PSI.
  • The absence of pressure is measured in “Inches Of Mercury” (in. hg). (Finally we get to use the periodic table of elements in real life!)
  • -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).

Now some of that good stuff:

With a N/A engine running, the MAP sensor may see readings » Continue reading more of this post…