P0420

So I have a the dreaded p0420 code on my 99 3.4 liter. Couple questions. I have have had a tick that I thought was a valve tick for awhile, finally took it to the dealer, and they say it's my coils and leads arcing out. That they look original (160k miles ). Could this cause the code from not burning the fuel properly? If not what route should I go to fix the prob? Check for leaks before the cat, and then start replacing stuff, starting with o2 sensors? Or just get URD o2 sims and delete the cat? Opinions? Thanks for the inpute

 

Last summer I had the 0420 code. Checked for leaks, checked cats with rubber mallet, tested temperature before and after each cat, and found nothing. Lastly I tested the resistance and voltage of the two sensors per the FSM. The rear O2 did not meet spec values. Got a denso and fixed it. No more code.

 

This is what I was planning on doing. Where can I find the specs for the o2 sensors?

 

You could put dielectric grease between the coil and the coil boot to stop arching also between the plug and boot

 

I'd rather just replace them if they're original. I was just wondering if it could be a cause of the p0420 cause it could not be burning clean