A scan gauge is one way to go, & that allows you to monitor a couple different functions, + viewing/clearing any CEL codes that may pop...in real time...on the fly...

http://www.google.com/url?sa=t&rct=j...X_-1-ygBqyxnmQ

http://www.google.com/url?sa=t&rct=j...aOPQnl0qoaW-Cw

http://www.google.com/url?sa=t&rct=j...DXvcCP6m731dog

OR...if you're of a more "old school" mind set, get yourself an inline bung, & go from there...

http://www.google.com/url?sa=t&rct=j...x38OV0y8PjGseg