I just bought a 1999 Ford Mustang. it's a 3.8L V6 with a manual transmission. She started up great the first time and i drove her home fine. I turned it off in my driveway for a while then came back later that day to start it up but she would just keep cranking and not turn over. And today it started up fine and then when i turned it off and tried to turn it back on it did the same thing, Cranking but not turning over. I have replaced the battery and alternator and checked the spark plugs. they're good. (I don't know alot about cars because im young and don't have much experience.) I was watching Scotty Kilmer videos about the issue on youtube. I tried the Starter fluid trick and that didn't work. I checked the lines and all that (they were bone dry) So im starting to think it's the fuel pump. i will go to prime the pump by turning over the key and i can hear it prime. Maybe it is pressure? Any help on this subject would greatly help. I will provide more information as it comes. Thank you!