These flipping mechanics... O2 sensor/wiring/exhaust problems

[wickedfrisone]

'06 base with 200k - just had to have the catted downpipe replaced to get rid of P0420 code and pass inspection - that code went away and all but the mechanic(s) screwed up and got the upstream O2 sensor wires stuck between the downpipe and exhaust manifold/gasket area. Threw like 5 new codes after that. There was also an annoying and nauseating smell of gas (not really fuel smell, that smells so much better) in the cabin when the wires were jammed in the pipe. I think the engine even did start misfiring occasionally when accelerating from a traffic light, and did through the P0300 code a couple of times too. The car was taken back to have them free up the wire. No more noxious fumes bothering us in the cabin. Appeared as though the sensor/wiring was toast anyway, codes weren't going away so a new O2 sensor had to be ordered and replaced that one. I think two of the codes went away after that, but we still had P0131 O2 sensor circuit low voltage B1S1, P0036 HO2S heater control circuit B1S2, and P0030 HO2S heater control circuit B1S1.
Last night my dad and I figured out (somehow not sooner) that we should check the fuse for the O2 sensors, since the wiring was fried when it got pancaked inside the pipe. Surely enough the fuse was blown, so we replaced it last night. Well, this morning the gas odor has returned inside the cabin after the engine runs for a few minutes. Codes are also still not gone as of now, but we haven't drive it enough I'd say to be sure they won't go.
I just can't wrap my head around how after replacing the blown fuse we have the same odor we did when the wires were in the pipe, which we assumed then there must've been a minor exhaust leak for obvious reasons. But why again now if there shouldn't be an exhaust leak, and only simply after swapping the fuse? The engine is also still occasionally misfiring which I also don't get exactly how it relates. I'm certain the O2 sensor we got wasn't AC Delco, which it might be worth trying another O2 sensor but would it not being AC Delco cause all of these issues though?
Thanks

 

[BillBoost37]

I remember you saying this and suggesting the fuse be checked/replaced as it would have blown. The smell you get may be due to the pcm adding tons of fuel while it couldn't see what was happening with the o2. Depending on how much it was driven, the cat could have been killed by the issue and I'd make the mechanics replace it again at their entire cost for parts and labor if needed. Meanwhile I'd take the car on a good highway drive so if any fuel is in the cat, it will get burned out.

 

[wickedfrisone]

I remember you saying this and suggesting the fuse be checked/replaced as it would have blown. The smell you get may be due to the pcm adding tons of fuel while it couldn't see what was happening with the o2. Depending on how much it was driven, the cat could have been killed by the issue and I'd make the mechanics replace it again at their entire cost for parts and labor if needed. Meanwhile I'd take the car on a good highway drive so if any fuel is in the cat, it will get burned out.

Hopefully the cat survives...wouldn't want dad to have to buy another. I mean, so far the cat code hasn't returned thankfully. So PCM is adding extra fuel while it couldn't tell what was going on with O2, before or after we replaced the blown fuse? That kinda gets me haha. That's what I thought was going on with my mom's car because all the time while driving you hear the fuel pump kicking in, and it does have the lean code, so I wondered if O2 sensor was giving incorrect readings about the air/fuel ratio.