Engine light on(oxygen sensor) replaced & light still on.

Has been sounding like bad gas under a load (pinging) and loosing power.
I did replace timing chain tensioner since it was due and actually sounded like it was loose under the load. (paranoia?)

Replaced fuel filter, plugs, wires and pressure tested fuel.

Replaced fuel pump w/ spare and no change.

Runs worse every time it is started. Sounds like it is starving for air under acceleration and some back firing.

Almost forgot, I also added a fuel treatment for the first time!

Any help would be appreciated.
this is my first time and have had some experience w/ the car in the lat 7 years of ownership but not much since it has been a dependable car.

114000 miles