Seriously though, back about 10 years ago tuners piggy-backed onto the signal going to the injector and extended the pulse width to make the tune richer. It only worked off the original ECM signal and a few other parameters (throttle position, RPM, etc...) Some of them are still like this (Dobeck) but also used O2 sensor eliminators to trick the ECM into open loop so the tuner would work all the time, not just at WFO. If you didn't bypass the O2 sensors the tuner would only work above 50% throttle when the ECM goes into open loop. Now I'm seeing stuff like the FP3 that somehow in all its magic alter the fuel map over CANbus without doing anything else. (I know what CANbus is, I just don't see how it can influence the fuel mixture)

My question is how does something like the FP3 alter the fuel map around the oxygen sensors and all the EPA's influence. From the looks of that thing it does a quick flash on the ECM, but I can't imagine HD and the EPA make it that simple, especially after the lawsuit.

 

The FP3 allows changing of the tables in the ECM so that you don't need the external device. I don't think HD has the ability to lock the ECM yet. I understand TTS, which is another flash tuner, can tho

 

So it can tell the ECM to ignore the O2 sensor feedback?

 

The differences between a flash based tuner compared to a piggy back. Piggy backs altered what the original calibration in the ECM was putting out. A flashed base tuning strategy is that you actually change the calibration in the ECM. This allows you to set the AFR to a richer switching point, reduce the size of the closed loop feed back or eliminate closed loop altogether. PLUS is will allow you to change many more things in the calibration as well.

 

That's an answer I can work with. My biggest hurdle was the damn sensors and how the hell do the tuner manufacturers make the most of a tuner with respect to leaving the O2 sensors alone.

For what it's worth, I emailed Daytona Twin Tec this very same question regarding their Twin Tuner, which I've used on a few Harley's and I love the operation of it. He confirmed that the EPA got involved a few years ago and put the kibosh on the O2 bypass plugs. They still sell them tuners but the O2 sensors in the circuit will screw with the tuning and make it harder than it needs to be. He also confirmed that if you can find the plugs it MAY still work, but their testing on a few of the 2017 bikes triggered a check engine light. Which code I dunno, he just said "check engine light".

Thanks everyone.