So shoot me, first post OBDII questions, P0420

So, I'm new here, and yes I did a basic search and I get the idea that these cars (mine is 2002 si with 192k) seem to go through catalytic converters over time. Mine is apparently on its third converter and is now again throwing a p0420 any time the OBDII cat test completes, which sometimes takes as long as several hundred miles, but usually it's less. I am attempting to sort this out and I have some quick questions:

BLUF (Bottom Line Up Front, for those that know)

1.Is the upstream sensor on a 2002 Si an oxygen sensor or an "air fuel sensor"?

2.Is what an OBDII scanner (using Torque app for Android) labels O2S11 always, really, the upstream sensor and O2S12 always the downstream?

3.Is it possible that some moron swapped the plugs so the ECU sees upstream and downstream reversed?

I ask because the data shows O2S12 ocillating regularly at idle, going lean on closed throttle, etc. exactly as I would expect from the upstream sensor, and O2S11 mirroring O2S12, but with a much smaller amplitude and some delay, staying more or less even at idle while O2S12 oscillates rich-lean, exactly like you'd expect from the downstream sensor on a good cat.

If swapping the plugs is impossible, then my guess is that the cat is in fact bad, and O2S11 simply looks odd because it is really an air fuel sensor being reported by OBDII as an O2 sensor because that's all OBDII can do.

For anybody that wants the whole story, because diagnosing codes does not occur in a vacuum of other relevant information:

The car also burns oil, so a bad cat would not be a surprise. The PO, a close friend (I am actually sort of baby sitting his car while he lives in Hawaii indefinitely, maybe I'll give it back, maybe not, we'll see) tells me it leaks, a lot, from the valve cover. I look at the valve cover and under the car, and he's full of crap. Yes it is weeping a little around the valve cover, but the oil is being burned, not leaked. Plenty, maybe 1 qt every 2 tanks of gas--driveable, but clearly something's up. Exhaust tips black, soot on bumper, but no visible smoke. I suspect problems with PCV system, notice that the upper hose from the valve cover to air cleaner housing has separated (well thar's your problem!). I've corrected that and installed a new PCV valve because cheap. We will see if this corrects the oil burning problem, probably should do compression test, but that will have to wait until I have a few more minutes to fuss with it...

If it turns out that his rings are actually that shot, I'll be less likely to replace the cat, if it's really bad, at least certainly not without rigging some sort of catch-can in place of the original PCV system.

I know this is not an uncommon problem--anybody got some quick answers?

I've answered my most critical questions, so I'll share what I've learned:

I am a bit surprised nobody on here would at least verify that the upstream sensor is an air fuel sensor (essentially a wideband) rather than a standard sensor.

This post on the Honda-tech forum explains what I am seeing:

https://honda-tech.com/forums/honda-...whack-3272201/

So, nobody switched the sensors but it remains likely the cat is not too happy--again, this is not a big surprise as the car is known to have been burning oil. On the other hand, it's also clear that the cat design and implementation here is not Honda's brightest moment, as my research seems to indicate that cat problems are one of the most common issues with this car. I don't have a stock cat to look at, as I suspect the one on this car is not OEM, as it is, I think, the third one, but I believe even from the factory this was a "high flow" design with concentric metal layers rather than the ceramic honeycomb. It is also tiny, and the downstream sensor is smack in the middle of the cat. I am not about to try it just yet, but I wonder if the best solution, at least from an emissions standpoint, would be to simply retrofit a larger ceramic cat with the downstream sensor bung in the far end rather than the middle.

It seems that using an drilled out anti-fouler as a spacer for the downstream sensor, even on a good cat, is what everybody does to keep these cars on the road, so that's what I'll do next and hope maybe the cat will also clean itself out a bit if I can keep the oil out of the combustion chamber. I haven't really driven far enough to verify that, but so far so good.

Don't be surprised, the forum's pretty dead.

I have had a Magnaflow cat on my car over a year now (bought the car 2 1/2 years ago), and have had no problems.

Don't expect answers here, unfortunately. Much better to go on the ephatch facebook group and ask there; that's basically where everyone went.

Did the PCV update do anything for your oil consumption? My '05 burns oil at a similar rate; I'm not fussed by it as I intend to do a motor swap in the spring, but if I could stem the flood I would.

I’m on my 3rd cat man(2nd replacement). Each time it’s been the p0420 code and each time a new cat has fixed it. The last cat was empty when I took it out, i guess all the honeycomb stuff broke and blew through the exhaust.