gtv-6 fuel consumption?o2 sensor?

[SPSNOWMAN@domain.elided]

         I'm pretty sure my car is getting terrible gas mileage,exactly how 
much i don't know.My speedo and trip doesn't work.For the past two weeks I've 
been using it as a daily driver,using Cheveron 92,and just driving around 
town,it's been sucking down about $40 a week.When the tank gets down to about 
1/4,periodically I start smelling a little bit of gas fumes coming from the 
back of the car,I checked for any obvious leaks,none.
         The oxygen sensor is disconnected,would that be the cause?There's a 
clean K&N drop in replacement air filter and the car runs like a 
champ.Otherwise everything is pure stock.
Any thoughts would be appreciated,thank you. 

Thanks in advanced
Giuseppe
86 gtv-6

------------------------------