Where is my gas going?

[Jdiddy2k4]

Hello, I have a problem with my 95 eagle talon n/t. I am driving down the road and looking at my gas to see what kind of mileage I am getting and it is pretty good. Sounds good right. Ok well next thing I know the check engine light comes on and then a 20mile trip made my gas tank go from 1/2 way to about 1/4 way full. It was like I had an H2 Hummer or something. What could be the cause of the gas going like that?

 

[Defiant]

Well, first huge duh is to have the CE code pulled.

But possibly more important is that the needle on the gas gauge means exactly shit. The only number that matters with mileage is miles divided by gallons. Miles per tank is meaningless, partly because DSMs are notorious for having some of the flakiest and most random gas gauges ever made.