it it the catalytic converter?

I just changed the #4 injector on my 2004 izuzu rodeo because my check engine light kept coming on the code that it sho shop was the number 4 cylinder misfiring I tested the wire and it was fine the compression was fine so the only thing I can think of at the injector I change that and it was its running perfect against a little stutter now it's giving me the p0430 code which indicates lazy sensor I don't know which one or a leak in the manifold or the catalytic converter I don't want to use a mechanic because they will charge me an arm and a leg. Has anyone else experienced this problem?

thats a bad catalytic convertor or bad rear 02 sensor or a exhaust leak . a new 02 sensor will be cheaper than a new cat. bank 2 is the driver side bank