Ok, so this is kind of a long story so let me first start off with the model. It's an 89 Mustang GT (5.0). About a week ago I heard a knocking sound coming from the engine bay, so I took a look and thought the sound was coming from the alternator pulley. I took the alternator to O'reiley's and they told me the alternator was on it's way out. so I replaced the alternator. When I turned the car on the sound was still there, upon closer inspection I found that the sound was actually coming from the smog pump. I decided I was going to bypass the smog pump because I was gonna save some money on a new pump and even gain a tiny bit of HP from the freed up pulley. I took it to the mechanic and he charged me 80$ to bypass it. I thought he would completely remove the pump and plug all the holes that lead from the pump, but all he did was buy a smaller drive belt and installed it without going around the pump. I'm not actually sure if he did anything other than that, he might of but I'm pretty sure that's all he did. Anyway, the sound was gone after that and all was well. A few days later I'm driving down the road and I begin to smell burning wire. I pull over and find that my alternator burned out, the smaller plug that connects to the alternator was completely charred black. So I take the car back to the same mechanic with a new alternator (I had a warranty on the old one) and he installed it for me, seeing as how one of the wires from the alternator had been burned, I didn't want to mess with it. So I finally get the car out of the shop this morning and as I'm pulling out of the driveway I noticed the car lost quite a bit of power. I took the car for a drive and whenever I give the car a considerable amount of gas the engine kind of hits a wall and accelerates very slowly. Also, whenever the car is in this struggling state it sometimes backfires if I had to guess I would say the car feels about 20% weaker.