Misfiring

I'm kind of new to pcm knowledge but i have seen other posts that warn to be careful when swapping engine components because the pcm is quite specific on many car models/years and everything must match up correctly. You need to find out which year your new engine came off of. Also, how many pieces/parts from your old engine were put onto the new engine? Some parts are not only electronically synced to a particular pcm but are also mechanically compatible or NOT with other mechanical parts (i.e. camshafts in particular). But if the new engine came with all of its parts and you also brought the pcm from the vehicle where the new engine came from (or was it literally new from the factory?). Anyways, a change in, for instance, fuel pump and its pressure could still cause problems. You need a specialist to help identify if everything is compatible. All that said, most pros tell you if one coil pack goes bad buy all new ones cause they usually all fail in close time proximity to each other. And if several cylinders are missfiring they could create a fuel rich condition and set a legitimate O2 sensor code. So, may not be the pcm at all...but still...may be. Gotta love it, huh? Cars are getting way complicated.