The anaconda down pipe is actually catless. If you look at the stock one, there is a catalytic converter between the 2 sensors.. The first O2 sensor is for air that is leaving the exhaust manifold. The second O2 bung is the outflow after the initial reading from the first sensor to make sure that the cat isn't plugged up or reading the same as the first o2 sensor. The 3rd bung is for a wide band sensor. Like I said before. I could be wrong.
2 of the holes are basically there so you have something to hook your existing O2 sensors into. The 3rd is for a wideband O2 sensor. Unless you have one of those, you'll simply plug the 3rd.
From MPFab's site: "This “competition” downpipe deletes the restrictive primary catalyst and replaces the secondary catalyst with extremely high flowing 100 cell MPFab unit." You are not going to get a clean emissions reading because you are running a catless downpipe (this is the same for ZZP's and BNR's catless downpipes). Even if there was a hole after the secondary cat for you to plug an O2 sensor into you probably wouldn't get a clean reading because the primary cat is responsible for most of the cleaning of the exhaust.
So you have a few options... 1) Live with a perpetual CEL... 2) Disable the O2 sensors using Trifecta's software (if you're tuned)... 3) I have had success running a Vibrant J-Fitting. This moves the second O2 sensor out of the exhaust stream and tricks it into reading clean.
Hopefully this clears things up for you a bit. 2 of those holes are where they are simply because they have to be to accommodate existing sensors.
4) live with the CEL? (Wouldnt recommend this, you'll never know if you have another issue...)
Realistically, you could remove the rear O2 sensor as it's only purpose is to check primary catalytic converter performance and use it as a WBO2 bung.
Great post and thread, but I want to expand on this a bit- so we could cut or simply pack up the rear bung and not use it at all. This would leave that bung viable for WBO2 down the road.
Obviously you would still have to deal with the CEL, but that's no different anyways.
If you have a tune, you could just unplug it and remove it entirely from the exh. system. You could in fact use that for a WB.
Will this J Fitting be the correct size with the Anaconda? 18mm x 1.5 male threads?