So my 97 GSR has been getting worse gas mileage than compared to a few months ago. I normally got about 31-33 mpg. I noticed, it dropped down to only 26-28 mpg. Same commute, same driving habits, etc.
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?

 

the lower the voltage the leaner the mixture on a standard O2 sensor. However a dead O2 sensor will also show low voltage. If you are seeing that high of an O2 sensor voltage and it is not switching any lower then there is a good chance you have a really slow or "lazy" O2 sensor or something else is wrong with the car causing it to stay rich all of the time.

 

It cycles between .075 and .785 fairly quickly

 

sounds like a bad o2. I had a similar issue, replaced the o2, problem solved

 

What were your voltage readings for the old and new O2 sensers?

 

Installed my new Denso OEM O2 sensor. New voltage range is .160-.820 volts. Will that help me get better mileage now vs. the previous sensor that read .075-.785.
These readings are from my Actron OBD2 scanner after car has gotten to normal operating temp and idling at 785 rpm.