Checking MAP sensor at altitude.

[altered7151]

I was sitting here at work thinking about checking my 3-bar map when I get home to make sure its reading correctly when it occured to me that I might have to compensate for my altidude. We're at about 4500ft elevevation here, which puts us at about 12.5psi ambient pressure. So when I check my map sensor should I be looking for a voltage reading that coorelates to this pressure? In other words at 0 gauge pressure should I expect my map to be reading approximately 2.2 psi vacuum (4.5in hg)?

[MiniMopar]

Yep, it will read lower for you. The gap under the sensor transducer is a nearly perfect vacuum (the "A" in MAP), rather than being exposed to the atmosphere. Mot did made a sensor using the same series transducers that measured relative pressure too. Had a pile of them in a box somewhere along with the stock 2bar MAPs that were given to us from the inside (old samples).

[altered7151]

Just read the map sensor at ambient and got 1.37 volts, so that works out just about right at 12.5psi atmospheric. Follow up question, Its starting to look like the barometric solenoid was stuck not allowing the MAP to read atmospheric conditions. Would this create the same effect as when the map line pops off? The map sensor seems to be reading fine, but last night it felt exactly like the map sensor line popped off.

[MiniMopar]

No, it will continue to measure the manifold pressure fine. There is some baro compensation that comes into play, butit shouldn't have a very noticable effect. You could have been in a limp-in mode though. If the solenoid was stuck open, then it would be exactly like a disconnected line.