I need to know how I can tell if an O2 sensor is bad. Do I have to put it on diagnostics or? I have a 97 F250 4x4 with a 5.4. You can smell what seems to be burnt gas, especially when you first start it up, or it sits at idle for very long. I have already had the egr valve replaced and the rest of the system cleaned. I have also replaced the plugs and two of the cop's. Truck seems to run good other than just a couple of small things like this going on. Any help, advice or thoughts would be great. Thanks.

 

Normally if an O2 is goin bad you'll get a CEL.