It's the addition of the headers that pushes the O2 sensors further downstream. Hence the reason headers that do this come with O2 sensor extension harnesses.

And there is no theory involved. It happens all the time. That's why there's a setting for it in custom tuning software called "O2 transport delay". The reason it says could is because every application is different. Example: car number 1 adds LT's and they push the O2 sensors back 6" from the stock location and car 1 experiences no issues. Perhaps due to the fact that while moved 6" the timing of the pulse and sensor read are still close enough to provide an accurate reading. Another example would be car 2 which adds LT's that push the sensors back 12". This results in an error code such as P1132 and P1151.

Another issue with LT installs that push the O2 sensors back is lack of heat. O2 sensors need temps above 600F to work properly. They have built in heaters which are also ECM controlled. If placed to far back in the exhaust system without telling the heaters to run longer you will get codes like P0135 - O2 sensor heater circuit malfunction.

Here's an excerpt from a tuning manual. The bottom of the page is regarding O2 sensor tuning.

 

So why do you think no other brands say anything about 2 or 4wd?

 

Yes I understand that's it's the addition of the headers that pushes the o2 sensors farther away. As I said it must be out of necessity due to the length of the primaries. Is this common with our trucks? I have not run into this issue with any FWD cars I have built or tuned for ice racing. In these cases the o2 sensor was far enough downstream to not be affected by the addition of a header. I guess it makes sense since in a RWD vehicle the primaries must be significantly longer to all point towards the rear as opposed to FWD where they can all meet in the middle.

Yes it would be a theory as not all vehicles are affected in the same way. Is there a max distance in change? Is it related to compression?

Lots to think about here. Very interesting.

 

Not sure what brands you have looked at and quite frankly it's been a long time since I went header shopping. But i do know Dynatech specifies 2wd or 4wd. The headers are the same part number but the mid pipe is different. Stainless Works uses a mid-pipe that clears the transfer case and uses it on both 2wd and 4wd. This makes the most since as the 4wd kit can be used on the 2wd with no issue. There's really no point in making two different mid-pipes.

 

I guess I'm not understanding what you mean by theory. Theory to me means it is a logical thought but not proven. This issue occurs in numerous applications. Mustangs, Camaros, trucks, Vettes, SUV's etc. You can google it and all sorts of threads and info will pop up on it along with complaints from unsuspecting consumers with CEL lights after header installs. Along with poor fuel mileage and performance as the O2 sensor readings are used by ECM to control the pulse width on the injectors.

And what you are saying about rwd verses fwd makes perfect sense as generally headers for fwd cars are not long and don't push the sensors so far down stream.