I know that kPa is a unit of measurement of pressure by the pcm, but what i dont understand is what the k stands for? I know that Pa(pascal) is a unit of measuement of atmoshere pressure, 1 atm=101,325 Pa, so why is 100 the max? How does the k change the unit measurement?

 

k stands for kilo. 1000Pa = 1kPa. So divide the Pa by 1000, and you get roughly 100kPa

 

That clears it up, but why didnt gm set the kpa to 101.325 for a more accurate reading? Or is 100 kpa just what the scanners use?

 

There is no "limit" of 100kPA.... a 1bar MAP sensor will generally output the voltage (5.0) that corresponds to over 100kPa. I've seen some scanner data logs where the barometric pressure (BAR) is reported at up to 103.7kPa. You generally do not see many readings over 100kPa for the MAP reading, since there is always "some" pressure loss through the filter, ductwork, throttle body, etc.... There's nothing magic about 100kPa, except that by definition it is "one atmosphere" in the metric system, which sets the standard atmosphere at the equivalent of 14.5psia, rather than the 14.7psia used in the English system.

 

Injuneer, that clears it up even more!!! I didnt even think about the fact the MAP sensor would just put out 5.0v for anything over 100kpa.

 

The calibration chart I have seen shows 4.9V = 100kPa.... so you would get a slightly higher reading at 5.0V.

 

I do!! I see 103.7kpa under WOT, but I'm adding a little air to the mix!