The computer has been programed to save the evironment and not the dollar. Laws require that automakers make it difficulf for people like yourself to mess with it and get better mileage. Environment vs. Money....... The age old question.The real trick is to convince the engine's computer nothing has changed, otherwise, it "adjusts" the fuel flow to "compensate" for the added oxygen the O2 sensor is seeing in the exhaust (thinking it's too lean, so it adds more fuel). The computers keep the "back yard" mechanic from getting more MPG from a vehicle. There is also information on those sites "how to trick" it to give you more MPG with an HHO to assist.
I have read about people injecting hot air, people fooling the temp sensors etc..... It does get you better mileage but at what cost. If everyone did it what would happen?
I hope that none of you that are for this kind of activity are voting for Obama......