So my 97 GSR has been getting worse gas mileage than compared to a few months ago. I normally got about 31-33 mpg. Then I noticed, it dropped down to only 26-28 mpg. Same commute, same driving habits, etc. I doubt the gas stations around here switched to the winter mix that has more ethanol or whatever, cause it is still hot here, and MPG went down towards the end of summer.

So I did a complete tune up, check out tire pressures, etc. MPG is still the same.

So I'm thinking the stock O2 sensor may be getting old. The voltage bunces form only .075 volts to .785 volts in closed loop.
I belive the manual says the voltage should bounce from .1-1 volts. Does a lower voltage reading mean a lean or rich mixture, and will that be the cause of the drop in MPG?

 

Well I would say that would be your cause for worse gas mileage. How many miles are on the O2? I'd say swap it out, and you should see a fairly decent change in MPG.

 

92k miles, any idea what the low voltage indicates? Lean or rich mixture?

 

.1=lean, 1v=rich. your o2 sensor should constantly go up and down from typically .1 -1 to maintain 14.7 to 1 A/F ratio. u can see this on a scan tool or voltmeter

 

sorry missed that u had a voltage reading. I would replace the sensor