How do I know if my O2 sensor may be bad
These *is not* a pointer to O2 sensor failure, just bring up the possibility. Vacuum leaks and ignition problems are the common fuel economy killer.
i) Fuel consumption increase
ii) Engine will lost power and not rspond quickly although done the normal tuning
iii) Gas from the exhaust smell like rotten egg
iv) No more water steam look alike came out from the exhasut tip (bad engine condition also happen like this)