98 Explorer getting progressively worse mileage

[paul_spunion]

Hey everybody 1st time poster here.
So I purchased my 98 explorer about a year ago. Then I would get about 250 miles to a full tank, now I'm lucky to get 150. Aside from that the fuel gauge is completely out of wack. I'll put in about 5 gallons, it'll say i have a little less then a half tank...then while driving drop down to a quarter tank. It just had a new fuel filter installed a couple weeks ago thinking that would fix the problem. I also just put in a new air filter and changed the oil thinking that would help a little bit. Nothing has worked. Has anyone else run into this problem and/or know what could be causing this?

Thanks!

 

[JDraper]

Have you calculated what your fuel mileage is, or are you going by your gas gauge?

 

[paul_spunion]

Not precisely, but if I put in 5 gallons I get between 45-50 miles in the city.