1995 Pontiac Grand Am Loud tapping under the hood

I had a head job done last July (2012) and now about 1 month ago I noticed some nasty tapping starting in my motor. I have a 1995 Grand Am SE V6. I have an oil change 3 weeks ago and they added a bottle of Lucas to that. Yet it still taps and I parked my car on July 4th and refuse to drive it any longer. The tapping is loud and obnoxious and appears to be upper engine area. I have been told no way to tell exactly what is going on until the motor is tore apart. The car still has power and no smoke out of the exhaust. It will periodically try to stall out (and has) at very slow speeds. Also, the computer of the care had to be bypassed a couple of years ago in order to get the cooling fan motor to work (linked direct to my battery and a toggle switch inside on the dash). I am wondering what could be going on with this car. Another thing is, when(which is rarely) but when I would drive on a straight shot highway, the service engine soon light would com on withing 5 to 10 miles of driving until the car was shut of ad then ran on a highway again. It doesn't come on when driving around town. Can you help me? Is it time to part with this car or is there still hope for it?


Thank you sooooo much