I got a http://www.scangauge.com/ so I could look at data live in my 5th gen A33 5spd maxima. I keep good track of my MPGs but I wanted to see more information.

I can look at 4 things at once. I usually look at fuel trims and 02 sensors.

Questions:
1) How do you interpret O2 sensor readings (the value is 0-99 which represents the voltage). I've noticed when I let off the gas, the values go down to basically 0.
2) Which bank/sensors is the most important to look at for MPG issues
2a) Should bank 2 sensors 1 & 2 and bank 1 sensor 2 all read about the same?
3) Fuel trims, generally my long term trims are around 0 and Short trims fluctuate from -9 to 3. I believe this is normal.
4) What's the relationship between O2 sensors and trims, which O2 sensor(s) are most important in determining fuel mixture.

I am still trying to maximize my MPGs and my car has 105K on the odo and most likely the original O2 sensors. I want to replace at least one (probably bank 2 sensor 1, is the most important) but I want to decide if I need to spend the money and I want to learn more about how to interpret what I'm looking at.

p.s. I am referring this great thread on the 02 sensors:
http://forums.maxima.org/5th-generat...bs-inside.html