o2 sensor. means oxygen sensor. without the computer knowing how much or accuurate amount of air coming in, it can't equate fuel air ratio properly or efficiently to give you good fuel milage. so yeah that will definitely mess with your fuel economy.

 

Thanks for all your replys. Will keep ya'll updated on this 6.7 -07 Ram and its performance. Other than these emissions problems shes powerfull as all heck. She idles my boat up the boat ramp!

 

I think when you loose an O2 sensor the computer puts the truck in a "limp mode". I know my 1500 gasser does when it looses an O2 sensor and the fuel mileage goes to cr@p.