i was throwing a downstream 02 sensor code before, so i replaced it, it was a bosch 02 sensor, it was premade to fit my o2 sensor connector so it snapped right into the socket, and i used the silicone stuff around the threads, and torqued it to about 35 ft/ibs. i then reset my ECU the next day, and that was about a week ago, and im still getting horrible mileage, i swear just 3 days ago i was at half a tank and now im close to empty, and i dont drive too much, and i dont floor it too much. and my CEL is not on, and i tried using that Gumout Fuel system cleaner and the mileage still remains the same. what the hell is going on?

thanks

 

downstream o2 has nothing to do with your gas milage. its just for catalytic efficinency. try doing a tune up and changing the fual filter

 

so its the upstream that reads the oxygen levels to the ECU? when i get my oil change ill do a full tune up and see if that helps, thanks for the help.