When asking for technical help at the very least let us know the version of firmware you are running.Cliff's Calibration (Mapping) Guide is a MUST READ: http://www.vemssupport.com/forum/index.php/topic,97.0.html
you dont even need to remove pullup, just calibrate it according to your stuff
Yes use the analog ground and you can use an external source as long as its all from the car.