P0420 Code Issues

[thardy3]

So, I'll start from the top. I've been chasing issues on my 99 2dr, 192k miles, since the beginning of 2013. It started with misfire issues, changed out plugs, wires, rotor, and cap. That did not solve this issue, turned out to be a bad catalytic converter. Swapped both out with weld-in MagnaFlow units and finally put mufflers on it while I was at it (truck didn't have mufflers when I bought it). This fixed the issue for about a week until I hit the highway for longer than 5 miles running 70 or so and it started missing bad. Ended up being a simple MAF sensor swap and she ran good for the next 3+ months. That's when the dreaded P0420 code came up. It was also sluggish in some stop and go traffic situations, kind of felt like a misfire. So I swapped out both rear O2 sensors with Bosch units. SES light has not gone away and it still stutters from time to time.

I've kinda run out of ideas here. Any ideas? Could the high flow cats be causing the issue? Could it be something completely unrelated to the cat system causing the code? Any help is much appreciated!

 

[SunlitComet]

use only delphi or delco sensors do not use bosch.

 

[thardy3]

Something told me that was going to be an issue. I've located the Delco part number for the bank 1 side (after cat), AFS106, do you happen to know the part number for the bank 2 side (after cat)?

 

[thardy3]

Can anyone help me out on my above question? I'm wanting to get sensors ordered for both sides (downstream), just want to make sure I order the right ones.

 

[pkupmanvt]

I don't know if you've fixed this yet, but the rear o2's won't make the engine run rough. The front sensors control fuel mixture, the rear's are just there so the ecm can monitor cat performance for emissions reasons. If the Mass air flow was bad you may have damaged the new cats by pumping too much fuel through them before the maf was replaced.

 

[SunlitComet]

Inaccurate info. The rear o2's do have an effect on the a/f ratio but it is just for fine tuning the mixture for the cats based on what the rears see. And the fronts are the same part number left or right. And a different part number for the rears left or right. so get yourself another AFS106 for the bank 2 post cat section of the exhaust.

 

[thardy3]

I swapped out the two rear O2 sensors and it became clear that my somewhat rough running was unrelated. We discovered that my brake booster was leaking causing a vacuum leak. We replaced the brake booster and she's running like a champ!

Also got the AC fixed, FINALLY!

 

[SunlitComet]

Oh that will do it for sure.

 

[thardy3]

Alright, so my P0420 code and rough running is back. The hesitation as previously described only went away for a day or two but it took upwards of 300 or so miles before the code popped back up. Any other thoughts as to what the cause could be here? I need to try and have these resolved SOON as I have about two weeks before I have to pass emissions here in GA. Any thoughts and suggestions of where I go from here is much appreciated, as I am 100% lost where to go next.

 

[thardy3]

Looks like I'm going to end up dropping her off at a shop next week. Really don't want to, but I'm tired of trying to figure this out. Let me know if anyone has any ideas.