hey jw i had a bad air pump in my 2001 blazer and fixed it but i noticed from the time my check engine light went on to the time i fixed it i only got about 11 mpg strictly city driving but thats horse**** i usually get about 15 city maybe 14...what do u guys get and do u think the air pump caused this

 

Its possible. The air pump is used to help with emmisions in your exhaust system. The O2 sensor readings have a direct impact on the computer, and the computer controls your fuel to air ratio based on the O2 sensor input. Yea, its possible.