mpg stumped

So after 9 months of work i got my 94 firebird back on the road. the thing gets good mpg over the halfway point then it rockets down to empty in like 9 or 10 miles. oh yeah after i hit empty i put 40 bucks in and filled her. other problem perhaps related was a hose slipped off and pisses antifreeze everwhere. fixed that but a day later anitfreeze came out of nowhere but it drives fine other than the gas thing. help a brother out!

I have a 1996 firebird- i think most likely your problem is a faulty gas gauge- once you get to half a tank you really have like 1/8 of a tank. My gas gauge was like that when i got it- it has gotten worse calibrated in recent years. When i see it hit half a tank I immediately refill it.