O2 sensors, exhaust leaks, and performance issues

[jasonoflivingston]

I have been watching my vehicle's engine performance slowly crap out here. Well, the other day, it went from a little lost power to wanting to hunt, stumble, and die at idle as well as run rough under throttle. I went in today and went over all of the hoses looking for a vacuum leak and found nothing, checked the plugs, checked the PCV, ensured the intake and throttle body was clean, cleaned the MAF (a week ago). No real obvious issues and no codes to speak of.

I have 186,000kms on it and the O2 sensors are likely original so I figured they could be part of the issue. In thinking about that, I started it up again and walked around listening (not sure why really. Just got me thinking about the exhaust and the cat). What I found was a horrible sound from the exhaust. I checked the muffler to find it split down the side, but as I got close, I realized that it wasn't what was making the horrible exhaust leak racket. It was the connection right after the cat. It looks like it has been steadily breaking down there and now it is definitely leaking and making noise. It just so happens that it is also between the two O2 sensors. Could the leak be part of the issue?

 

[JRZEE2000TR4LTD]

What do you mean "breaking down"? Are the flanges rusted badly that the welds are leaking? Hopefully the pipe with the cat (one cat or two?) on it is OK. If that's the case I would replace the muffler, tailpipe, flange gaskets and both sensors (just because of age)
With that leak, you could be getting some false readings, so if you just wanted to fix the leak 1st and see where your at, I guess you could do that.

 

[jasonoflivingston]

It is mostly the gasket that is the issue, but there is some pretty sketchy rust buildup on the muffler side (lucked out on that one). I only have one cat for reference.

I will be doing some tune-up work shortly as well as replacing that horrid muffler, but I am trying to isolate the main issue to improve my repair knowledge as well. You don't really learn much by chucking parts at it randomly and coincidentally fixing the problem.

Any ideas on how to do a quick and dirty plug of the leak to see if it is the issue?