Been looking into cleaning my O2s...as far as I know, they are original to the car and with 240k miles they have to have some deposits. What I noticed watching live data on the UG is that the car seems to be insisting on a relatively rich trim. Long trims run about +5 to +7, but short terms seem to run between -2 and +4. They never exceed + 10 or - 10, which is good, but the sum of your long and short terms should be closer to zero.Would this help? Would I notice an increase in FE? I am sure it does the cat no good - maybe that's what has caused it to fail 18 months after I got a new one? Or does the Echo simply run a little rich?