The internal MAP sensor on the EM2 is there only for installations without an EC2 (I.e. Lycomings and a few other diehard carburetor users : ).  Since the same calibration constants are used for both sensors, only one of them can be correct.  Obviously you should calibrate using the "EC2 on" sensor.   EM2's not shipped with their companion EC2's are roughly calibrated with the bench test EC2 and so may require re-calibration with your EC2.  Best way to do this is to adjust sensor offset on MAP channel (#25 I think) until reading matches your current absolute barometric pressure.  Use 30" - 1" per 1000 ft of altitude and it will get you close enough.

 

Tracy Crook

 

Bill Schertz
KIS Cruiser #4045

When the EC2 is off, it is using the reading from the sensor in the
EM2. When it is on, it is reading the sensor in the EC2. I have also
found considerable disagreement on these sensors. I also found that I
had to change the calibration on the MAP pressure channel on the EM2 to
get the correct reading (with EC2 on, we don't care what the sensor in
the EM2 is reading). I have no idea why the calibration should be
different on different units that use the sam e sensor; but there it
is. You can get a vacuum gage (actually a pressure gage, so you have
to subtract from atmospheric) at a reasonable price from McMaster-Carr,
or I could loan you mine.



Also, it should not necessarily read the barometric pressure; you have
to adjust for altitude. Barometric is equivalent sea level (or
something like that).