i just did a head n cam swap. and i finally took it up the road today and it seems like it has no power whatsoever at low rpms and its missing throughout the rpm range. would an O2 sensor make it run crappy cause i have datamaster and scan master and the both say its running lean. the right one that is. i had a header leak but i fixed that and its still doing it. the right one is reading as low as 200mv at times

 

sounds like a dead O2 to me!

 

Make sure your O2 wires aren't resting on an exhaust pipe. I was getting a false lean indication from one of my O2's from the wires resting on my Y-pipe.