Craig you have spent so much money changing things lately your car should be perfect by now.It obviosuly isn;t up to par. I can;t remember if you chaneg the wires plugs and distributer cap+rotor if not that is your first problem .Also get a motorvac done. It will clean out alll the carbon and make you spank the sentra next time.It is a high pressure fuel rail treatment that cleans the rail,injector,maniold,valves,combustion chamber,exhaust manifold,and especially the cat . It comes in very helpful when trying to pass an emmision test as 99% of all cars who get one pass any emmision test as the cat is so clean it will eat anything left over bfore the tailpie gets it.
Is you tailpipe black? If so then you are not buring you fuel right. I knowall cars do produce some smoke. But i only wipe mine down every so often and it comes out perfectly clean every time, Compared to my civic which runs really rich and is black out the back.