probably not the case but if nothing works your check engine light could be fried...happened to my buddy, he finally took it somewhere and found out it was throwing codes.

 

My O2s have never been changed.

 

Check the gas pump next time you fill up for a sticker saying what % Ethanol is used at that station. They are required to post this on the pump, but it is not always there. This happened to me a while back in dallas... noticed a big change in MPG. The station had switched to gas with 20% ethanol. After about a month they changed back to 10%. It is enough to make a noticeable difference.

 

[QUOTE=dixiedesign]Hey guys, I'm curious if anyone has any ideas why my MPG have significantly dropped. I was getting approx 19MPG on my 04 4.6L after installing an S&B Air Intake Kit. I consistently got 19MPG for about a year and a half, then all of a sudden I'm sitting at 14 or 15MPG. My driving habits have not changed, and I always fill up at the same gas station. My first thoughts were maybe my O2 sensors have gone bad, but wouldn't that set off my check engine light? I've got 80,000 miles on my truck, and haven't done anything engine related other than the air intake and scheduled maintenance. I am a do-it-myselfer but this is the first vehicle I've owned or worked on newer than a 99. Any advice would be greatly appreciated!! Thanks!

Neal[/QUOTE

did your intake come with a new mass air flow sensor, if it did it may be reading false and causing your computer to adjust for the bad reading. you can always swap out the maf sensor or put your old intake back on to see if your mileage gets better also could be time for spark plugs based on mileage.

 

check the air filter to see if its real dirty if so just clean it and try it but if you do, remember it wont be like it was when you first bought the intake.