the TTS MasterTune will use the factory O2 sensors to tune the bike without a dyno...
it works really well!

 

the 02 sensors are used to maintain a AFR ratio of 14.2 to 15.4 depending on the voltage applied. the only way to accurately change the voltage is with a tuner that allows access to closed loop bias. (CLB). while this works as described in stock configuration. stock bike stock ECM will use the 02 sensors as a switching device to maintain 14.7 Stoichiometric. the stock bike is calibrated to this 14.7 stoich . so now the closed loop operation will be able to maintain this 14.7 AFR as long as there isnt something that causes it to go outside of there (sensors) parameters of 14.2-15.4. (they are only able to read this area) anything outside of this area and they cant control (maintain ) fuel (AFR) or injector pulse with accuracy. that is why when you do a mod that leans the bike out (even more then they are already) it drives it past the 15.4 AFR limit of the sensors capability,and can cause the motor to go dangerous lean because they cant drive it back into there capable limits.
so yes if you modify the bike in a manner to lean it out or richen it up(pipes ,A/C, cams,head work ) it will need tuned. the best way is a good tuning device that allows access to the ECM to re- program, it also needs a GOOD dyno man to determine where it's at and what it needs "everywhere" not just at idle and wide open throttle.
the reason fuel management devices that just add fuel everywhere are not acceptable is because they add fuel everywhere, and diff pipes and or mods will need fuel taken out in some areas ,and fuel added in others.
dealer downloads are a whole other subject. they are still closed loop and therefore EPA compliant. sometimes they are close enough to work and other times the bike will run worse after the download.
tuners with canned maps are generic. they are for a specific combo, if you combo is diff in any way they wont be optimal. even when the combo matches exactly,the injector flow rate wont be the same as the canned maps bikes flow rate,and the heads wont be the same cc's so the compression of the two bike will be diff causing the motor to have a diff efficiency . thus changing AFR.
Lots of myths about the stock sensor being some kind of magic cure for always maintaining "close enough" AFR . it is just not true,I have seen a set of pipes and A/C cause a motor to go as lean as 17.4,and then have a area right beside it as rich as 12.8,when it really needed to be 14.2 in that area.

 

Thanks for all the info, guys.

This came up after a breakfast run the other day. I was saying that I intend to replace the stock mufflers first. Next would be the AC and a tuner. Then the head pipe. One guy at the table was saying that I could do the mufflers and the AC before needing a tuner (because of the O2 sensors). That's what led to my question.

Given the info I think I'll stick with my original plan.

 

So, what's the fuel ratio if the O2 sensers are just unplugged?
I've done this on my '10 Limited, runs real strong and a lot cooler, gets 40 mpg,
no popping on decel, plugs are now looking nice an tan, inside the mufflers look richer but not black and sooty, (not dry and rusty like my friends '10 ultra that is completely stock).

 

Ideally you want to save up and do all the performance mods and get it tuned with your tuner after you instal everything. Not get it tuned and then change something i.e. your headpipe.

 

Tells your engine where to ping a little of ping a lot!!

 

please explain this theory