Ok I have a 94 ls in an eg coupe and thought this would be the proper place to post.I dont post much due to the magic search button and vast knowledge on HT. I was getting 350 miles to a tank (11 gallons roughly) without an o2 sensor. I bought an NGK sensor and milage went down to 275 a tank.WTF. I have about 10k on rebuilt head. Everything is new wires,plugs, filters, etc. Good alignment and tire pressure.No CELs at all.How does milage go down?This is in town, no hwy driving and stop lights are far and few in between.I dont drive wth the pedal matted but im no grandma either.So i gues my ? is what now?

 

Have you had a "tune up" since you installed the O2 sensor?

Any CELs? 94

 

Do you have any check engine codes? Did you clear the codes when you installed the o2 sensor?

 

I was throwing the cel code for the o2 sensor (I believe it was 17) when i didnt have an o2 sensor but since I replaced it i cleared them and havent thrown any codes since. No I have not done a tune up since I replaced it. I measured the tank of gas right before I replaced it and the tank directly after if that helps.