if its sucking air its empty.

when my low fuel light comes on the first time on flat ground, i have 4 to 5 gallons in the tank still. best way to test this on your car is to run it till the light comes on, then top it off. note the gallons pumped, you have a 17 gal tank. ive never put more then 12 to 14 gallons in even when i was on the E line pretty much.