Did you reset tank with LEFT and MIDLE buttons?
1. You have to tell what distance and tank usage shows OBDuino
Not in setting, but one of PID's,
By default you see these number on 3rd screen.
2. Clear all memory with
http://www.arduino.cc/en/Tutorial/EEPROMClear
Upload OBDuino, and report same numbers after driving few km.
(do not change any settings).
Or did you modified code?