MAP sensor

[ned]

Should the MAP sensor reading match the barometric pressure from the ASOS when engine is not running? Mine reads .5 different.

 

[mmarien]

I don't believe it should. Here is some good reading on MAP.

http://www.avweb.com/news/pelican/182081-1.html?redirected=1

This is a quote from the article.

It is a good habit to note the MP gauge reading before engine start, and do a quick calculation to see how close it is. Set your altimeter to the field elevation, note the altimeter setting in the Kollsman window, subtract one inch per thousand feet above sea level, and your MP gauge should show very close to that value with the engine not running. At a 6,000-foot elevation airport, for example, set 6,000 on the altimeter, read (say) 29.5 in the Kollsman window, subtract six, and check that your MP gauge shows approximately 23.5 before start.

 

[dynonsupport]

MAP is only equal to the kollsman setting if you are at exactly 0' MSL.

The Kollsman window is the pressure at 0', even if you are currently at 4,000'.

MAP is the current pressure you are at. So they only match when you are at 0'.

If you want to check your MAP, adjust your kollsman setting until your altimeter reads 0'. Then they should match. This only works if you are close enough to sea level that you can adjust that far (about 3,000').