High fuel consumption

[Evgeni]

High fuel consumption could be anything from a vacuum leak, leaking injector a ruptured fuel pressure valve to a faulty o2 sensor.
You know your car the best and if you are suspecting the O2, you will need to backprobe the signal voltage to rule it out of the equation.
There are 4 wires. The two that are the same colour are for the heater circuit. One is a ground and it needs to read under 100mv. The signal wire will have voltage fluctuating between 0.1v to 1v in closed loop.
To verify it's integrity, force the car lean by pulling off a vacuum hose and creating an air leak. The voltage should drop to 0.1v and you should hear a change in the rpm.
Conversely, create a rich condition by squirting propane into the intake snorkel. Voltage should rise to 1v and RPM should change.

What this tells you is that the O2 is responding to change and the computer is adding or taking fuel away to counter what you are doing.

If this all checks out, your problem is elsewhere.