so i have a 94 corsica. when i look at the fuel gauge before i turn on, it reads half tank. but when i turn it on, it goes down to near empty. it's been about a
eek since i put half tank onto it. im not sure if this is a sensor problem or if i really am running out of gas. only had it a week & i haven't gotten used to the differences from other cars ive driven

 

When it reads near empty go to a gas station and fill it up. See how many gallons it takes and compare that to the capacity of your gas tank. You can also check the owners manual to see how many gallons it holds.

 

top off the tank, test the gauge again the same way.
if its reading empty when you have a full tank, its a bad sending unit.

They go bad 2 ways, they read full almost always, or read empty almost always.
My car always reads full, I just measure the mileage because I know how many miles I can go on my tank... I'm too lazy to replace my bad sending unit in my Beretta. Scares my friends. haha