I took them out and soaked them in petrol over night. Do you think a replacement would fix my issue?
Yes the parts changing brigade will tell you to change your oxygen sensors without even knowing or testing if they are fully operational or not.
There are numerous causes for rich running and the cause in your case if running rich is indeed the symptom may have nothing to do with the O2 sensors.
The first thing you need to do is have the engine scanned to see what fault codes may have been generated . This will give a clue as to where to look for issues which in fact may only be on one bank of the engine rather than both. So any fault that is going to affect both banks of cylinders won't be a cause if it is a just bank 1 fault or just a bank 2 fault .
Yes you can go and change all the O2 sensors but if a number of leaky fuel injectors is the cause of the excess fuel consumption replacing the O2 sensors if they are fully operational is going to do diddly squat.
Like wise a faulty CS. The coolant sensor monitors the operating temperature of the coolant that is circulating inside the engine. If the sensor is defective and reads lower than normal, or always reads cold, the engine computer will keep operating in "open" loop and the fuel mixture remains rich. A richer fuel mixture is required while your cold engine is warming up to prevent it from stalling. But if the mixture remains rich once the engine is warm, it wastes the extra fuel and will cause poor fuel economy.
There are numerous other issues that could be the cause so you need to do some proper investigation before just replacing parts and hoping you stumbled on the cause especially without even testing those parts for performance.
