only California bikes come with an o2 sensor from the factory. The only time you need to add one is if you are using a closed loop processor. When you use a closed loop processor you have no control over the computer, its a "closed loop". What the manufacturer of the processor has built in that is what you get, all controlled by the O2 sensor. So your bike is going to be set to run the way some guy in Frostbite Falls wants it to run. With a PCIII USB, and a good tuner given the right info from the owner, your bike can be set up to run just the way you want it. You ask how can the milage be better, I told the tech that made my map what speed range I cruised at most of the time and he set that range up slightly lean, better milage. The shop that did mine was Sabin Performance in Dallas, Does good work. Jim
He is real good. He was one of the wrenches on the world record holdin roadstar warror. you can read his bio at www.metrictech.net. How have you been anyway?