Over the weekend I decided to put on my Pacesetter Header w/downpipe for my NT 2.0 but go figure the guy who I bought it from didn't send the complete kit. So I had to get exhaust piping and I had a mechanic friend of mine weld the missing piece... he cut half my test pipe to make it work. Well... here's the problem:
Car seems to be running lean...
It seems like I'm not getting any real gain or power until I'm in 3rd gear at WOT around 4,000. The rest of time it seems like I'm not going anywhere just making a lot of noise
I don't have a wideband or anything like that... just a regular air/fuel ratio gauge and at idle it lights up 1 bar in LEAN and then fades off and keeps coming on and off. When I drive it goes crazy like the rest of those air/fuel ratio gauges but then when I stop at the redlight it does the same as if it was parked running... 1 bar LEAN fading on and off.

Now I was told today I don't have any back pressure and I need to put a catalytic converter back on to fix the problem. That my gas is burning too early.

Any thoughts what it could be? I know the car was running fine before installing the header and the extra exhaust pipe.