[V8] Code 2341 - disconnected OXS, still rough, plus exhaust hissing

[Karl D. Middlebrooks]

V8 #2 (dubbed "The Bismarck" by my girlfriend) has had a problem for a while that's kept it mostly sidelined. Since it's nice and sunny in the Portland, OR area today, I finally got around to having a look at what's going on.

Symptoms: sort of a loping idle (not horrible, but you notice it), no knocking sound during idling, some moderate-to-severe knocking on acceleration, low acceleration power, pretty miserable mileage, and I blinked out code 2341 today. 

The archives suggested disconnecting the black OXS wire, so I did that. The result was a reasonable increase in power, but still a fair amount of knocking going on during acceleration. Also, just for grins (and since I hadn't done it before), I checked the plugs. Passenger side plugs looked OK, driver's side were in awful shape (two had gunk in them that completely closed the gap), so I popped in some Autolite 103's throughout the car. Plug wires seem to be in good shape.

Now with the OXS disconnected and new plugs, power is noticeably better than it was this morning (still not where it needs to be), and I still hear knocking on acceleration. Code 2341 is still there, too.

Looks like 2341 suggests a possible exhaust leak, and I've noticed before that there's a hissing from the rear of the car (louder on the driver's side, still audible on passenger side); I'd made a mental note to check this earlier in the winter, but I'm a wuss about working outdoors in cold weather.

So, what would you folks suggest as the next step? If I want the exhaust system leak tested and patched (if needed), should I take that to a muffler shop for that? Should I check out the FPR as long as I'm working on this problem?