1992 Ford Taurus cranks but will not start

1992 Ford Taurus V6 3.0L 175000 miles I have replaced the spark plugs & coil, checked wires and distributor, the car is getting spark but when I try to start the car, it sits there and cranks and cranks but won't turn over. I have check the fuel pump you can here it running and the filter both working but it seems no gas is getting to the engine. I even called a Ford garage and he couldn't give any suggestion other than bring it to his garage so he could hook it up to his diagnostic machine. There's got to be something I'm missing. I was driving it home from work and it lost power for a second then came back running then a mile it did it again. I got it home but the next day it ran than turned off then it rough idled for a minute, tried to give it gas and it lost power then backfired. Today I tried starting it and it just cranks.