i dont think the downstream (rear) o2 sensor has anything to do with the trucks air/fuel mixture. its just there to make sure that the cat is working good, and to throw codes when people try to remove them lol. i cut the cat off of my 01 ram 318 and put 2 spark plug non foulers onto the downstream o2 sensor. works perfect. truck doesnt run rich, plugs dont get fouled out, and best of all, no check engine light. google/youtube the spark plug non fouler trick

 

The upstream O2 helps determine air/fuel mixture. If it is gone you run rich.

 

It was determined by a member here (cant remember who) about a year or so ago that the post cat o2 does play a roll in a/f mixture. It doesnt do a lot, but does have a slight impact on it.

 

I remember hearing that too somewhere, like you said it didn't determine much at all but did have a slight impact on the a/f mix

 

It does have a very minor impact on A/F. Non fouler is not enough to throw it off by much if any at all. And IIRC, the member that was experimenting/researching it is drewactual .

 

Yep thats the guy! I could picture his avatar but not his name, lol

 

Ok, now read the other thread where I ask what part of NH you live in.

 

Hmmm, and where would I find this thread? I even searched for it

 

hmm thats strange i didnt know that! but good to know too! with that being said i may just go ahead and get a custom tune. my truck needs it anyway with a CAI and no cats. thanks for the replys!

 

I'm thinking your truck does not need a custom tune for a CAI and no cats. Just needs the o2's in the correct spot's and a non fouler(s) for the downstream o2's and canned tunes.