I have Mazda 6 4 cylinder 2005, lately I am having problem getting the estimated miles per gallan. Which are 23mpg city and 28mpg hwy. With full tank of gas I used to get around 400 miles but now it's only 280-300. What could be wrong? I went to the deler service and the guy tells me that there is no way to fix that problem, thats the way it is we can not do anything about it. That I don't believe. Can someone please tell me what's going on and what I need to do about it? I changed the spark plugs and the wires.

 

may be dirty mass air sensor, clogged EGR valve, bad O2 sensor, or a combination of them. there may be more suspects but that's all I know of.

 

Over the last few years, the US Government has allowed refineries to include up to 10% ethanol in our gasoline w/o any warning necessary to the buyer or by the reseller (fueling station,) though most do have a sticker at the pump.
Because alcohol carries with it it's own O2 molecule, the FI system in the car must increase the amount of fuel delivered to maintain optimal fuel/air ratio. This has the affect of reducing MPG's.
My guess is this is all you are experiencing. My own mileage has dropped 2-3mpg. There have been a lot of questions concerning mileage lately, including my own. Since it seems to be so widespread, this is the only explanation I can attribute it to.

 

here in Oklahoma, it's state law to post on the pump if it's got ethanol or not. which is a good law and should be nation wide

 

It might be in Texas also. I know I see them at the places I go to for fuel.
But I had heard/read that the Feds eliminated the need for the information sticker a while back. Maybe that's right and maybe it ain't?

 

yeah there's no tellin with the feds