Mileage really bad now

My mileage has been bad for the past year and half.
Before I was able to get 250km average before the needle on the gas gauge went half way. Then it became 200km halfway…now i’m barely making 120km. Note these are mainly city driving. It was highway…I would be crying.

I’ve changed my spark plugs, spark wires, fuel filter couple months ago. Just recently changed my oil. Had the MotorVac service done 9 months ago. Mileage did get better but nothing close to what it was before.

I have yet to change my o2 sensor. I’m pretty sure that is one of the main problems (ecu has yet to throw an error code though) but I’m wondering what else may be the culprit?

Do you always fill up at half or what? Figure out how many L/100km you’re using – maybe your gauge is losing its accuracy.
But if you’re sure it’s chuggin gas, yes a new O2 sensor is a good idea.

How is it running? Acceleration smooth? If not, I’d suggest trying a new distributor cap & rotor. If the ignition’s not working properly, your mileage will drop dramatically.

Also, do you ever run injector cleaner through your system or have you ever taken your injectors out to get them cleaned?

Oh I always fill up…and I do calculate it. Last time I checked it used around 33 L for 240km. Not very good eh?

the Motorvac thing cleans the fuel injectors i believe and get rids of deposit of carbon and other stuff. BUt I also do use those injector cleaners and gas treatments that u buy at the local gas stations.

Not sure about rotor but I replaced the distributor cap same time as the fuel filter and spark plugs.

Bad thermostat? When I replaced mine, the gas mileage soared back to normal.