Turbo6TA

In fact, my Pfadt headers have bungs for the rear O2 sensors ... right behind the cats in the intermediate pipes.

I assumed they all have this.

Dano523

Because high flow cats are moved too far away from the head heat source, and if the rear 02 where still in play, then the car would be throwing codes since there was not enough differance of a read from pre to post O2 sensors instead.

As for defouling couplings, they just pull the rear O2's out of the exhaust stream, and even without cats in play, and you will still get enough of a differential reading of the pre and post O2 sensors to not throw codes as well.

As for the rear 02 bungs in X pipe, there used to install 02 sensor for a smog visual inspection tests when needed, but the rear O2 sensors are still tuned off in the tune (or defouling couplers used to pull the rear cats out of the stream instead). Really, most add the rear O2 bunges in, so the kit does not have to be labeled as off road use only instead.

Hence if he did not have codes now with the high flow cats in play, he is not gong to end up with codes by removing the cats now.

Turbo6TA

My Pfadt headers / intermediate pipes actually have 5 bungs total.

2ea pre-cat in the headers

2ea post-cat in the intermediate pipes

and an extra bung for tuning (for a screw-in style wide-band sensor if used for tuning)

Dano523

And again, with the high flow cats moved past the collectors on the long tube headers, will not be a great enough differential reading from the pre-02 sensors to the post 02 sensors, and the car is going to throw codes with the cats not being effective enough when compared to the OEM cat that where location way back up line instead..

The only way to prevent this, would be to go in the ECM programing to change the differential amounts that the unit is using to gauge the differential readings of the pre and post 02 senors to lower differential reading, and no tuning software with get you that deep instead.

So an x pipe can have all the bunges is wants for sensors, but when you install long tube headers in a C6 with high flow cats, you turn off the post 02 sensors in the tune, since again, they are only monitoring the performance of the cats themselves (differential readings pre and post O2 sensors to verify the performance of the cats).

Hence even with a lean turn for both close and open loop, your still going to get codes, since as you give the car gas to make both pre and post 02 sensor voltage climb like normal, the high flow cats farther down line will not burn off the excess fuel/rear O2 sensors drop their voltages down fast enough for the ECM, and it going to throw a code.

So again, the reason that manufactors install the rear O2 sensor bunges to begin with (oem provisions), is if there was no provisions for the rear o2 sensors instead, then the pipes would have to be sold as "off road use only".


As for wide band sensor port, you want it before the cats, not after them instead.