O2 sensor stuck lean

Bad sensor, vacuum leak, stuck intake valve or bad valve seats, manifold leaks, piping between MAF and throttle body, bad fuel injector, low fuel pressure can all throw the mixture off. Usually the computer can detect which sensor isn't changing and that's what throws the code, but it can be confused. For instance, our Honda CRV threw a catalyst code but it turned out that the oxygen sensors were old and updating slowly. Our BMW 325i threw a MAF code but it turned out to need an intake valve adjustment. My 5.3L in my Tahoe threw a MAF code but I knew it was actually the intake manifold needing a new gasket because it idled rough and I could hear it whistling.

If you've replaced the O2 sensors more than once, it's probably not that. If it's just one cylinder having a problem you can often tell by pulling the spark plugs and looking for the one that looks the wrong color (they should be tan like a lightly toasted marshmallow).

Full disclosure, I have a 5.4 V8 and from what I understand there are several things that can throw a code. IMO sometimes it is best to go to the vehicle dealer for troubleshooting and save some aggravation. My dealer pinpointed the one O2 sensor out of the four that was causing the problem ... driver side down steam after the cat.

Changed one O2 sensor myself for less than $30. Problem gone, no guesswork.

chryslermastertech wrote:
02 sensor is the result of another problem. stuck lean means the sensor is trying to lean out the fuel mixture in other words its running rich, the pcm is tryint to lean out the fuel.

Vehicle O2 SEES lean, then the PCM will richen the mixture up to a point like +20% to 25% and if still lean will throw a code.

Most likely vacuum leak, exhaust leak, bad or lazy O2 sensor, dirty or faulty injector(s), low fuel pressure.

It is idling fine and no heat issues. Seems to run and idle smooth.

02 sensor is the result of another problem. stuck lean means the sensor is trying to lean out the fuel mixture in other words its running rich, the pcm is tryint to lean out the fuel.

Check the PCV hose connection at the rear of the throttle body.

MAF (rare) would be lean on both banks. Can clean it but be careful, will not fix your lean issue
Any exhaust leaks?
Never replace a Oxygen sensor for lean codes (heater codes probably)
Likely vacuum leak, possible low fuel pressure but doubtful.

Adam

You should try asking this this question in a Ford Industrial Truck forum of some kind.

Or, a Ford V10 Forum or, something like that.

Moved from Forum Technical Support

Really does sound like a vaccuum leak...is it running hot ?

That sensor has been replaced twice in the last month.