This car is giving me fits!!

[Maxx]

Just bought this 91 240SX. I have extensive mechanical experience but this one is stumping me! The car had a bad alternator when I purchased it, but it ran great! I installed a new alternator, and it ran fine for a few minutes and I shut it off. Later it would'nt start. Engine cranks fine, it's got fire, and I smell LOTS of fuel! Next step, I clean the O2 Sensor, car starts up great! I drive it to the gas station to fill up, car dies and won't start again! Stranded! Next step, I replace the o2 sensor with a new one, start the car and drive it home. OK maybe it's fixed? WRONG! Now, when I can get it started, it barely drives, emits black smoke, and constantly threatens to die on me, and if it does die, I have to go thru hell to get it started again! Any input would be great!

[oki_bum]

is the tiny ground cable connected to the alternator completly on?

[Maxx]

Yes, I went back and double checked everything involving the alternator installation just to be sure. Maybe I accidentally switched the two wires on the back?