could 02 sensors be bad and not show cel?

[Mikes06GT]

Long story short, was having car data logged and my drivers side 02 sensor is reading 16% off from passenger side. Car has about 100k miles and they are original so replacing but just figured would have thrown cel code. I run an off road x so just replacing the fronts. He said an exhaust leak could cause also ut stock manifilds and x pipe is not leaking that i can tell. New 02s ordered. I was just curious why no codes.

 

[swflastang05]

Long story short, was having car data logged and my drivers side 02 sensor is reading 16% off from passenger side. Car has about 100k miles and they are original so replacing but just figured would have thrown cel code. I run an off road x so just replacing the fronts. He said an exhaust leak could cause also ut stock manifilds and x pipe is not leaking that i can tell. New 02s ordered. I was just curious why no codes.

Yes I've had bad O2 sensors in my car that caused some crazy short term fuel readings during a tuning session, there was no CEL on my car at the time.

 

[cyclerick]

Yes I've had bad O2 sensors in my car that caused some crazy short term fuel readings during a tuning session, there was no CEL on my car at the time.

Same here.

 

[Mikes06GT]

I replaced them today. Actually saw when I pulled them the passenger side had been replaced before. The front driver side is a blast to change! Lol I did notice car felt a little smoother although did not drive much. Just ran a little to do new data log. Hopefully numbers seem right now.

 

[Mikes06GT]

Doesnt look to be the 02 sensors were the issue car idle still dipping to 400 every time I stop and threw P0171 lean code again. Getting frustrated beyond words

 

[Redline727]

Sounds like it could be an unmetered air leak. Look for air getting sucked in the motor after the mass air flow sensor. Additional air coming in that is not accounted for can cause your symptoms and lean code.

 

[Mikes06GT]

So as random as can get.. A buddy thought his tb was bad. He came by yesterday to try mine to see if corrected his problem. Well as so. As we start his car idle is dipping and running like shit just like mine. We throw his on my car and my car ran great. I then noticed mine was caked in black by the blades. I cleaned it and car idle is 100 times better. I am going to replace as it still felt better with the other tb. Now. I drove for about 10 miles, car feels great but still threw P0171. Can a bad tb cause a lean code?? Now maybe it was in que and coming up from before. I cleared it. Time will tell but at least idle is fixed!!

 

[Mikes06GT]

It appears my LT fuel numbers were tune related. Had a Bama tune. hoping a new tune will keep numbers in check and p0171 code off. Also have a broken screw in my MAF housing were sensor goes. I have run this way for years with just the one screw and no issue. I'm wondering if a little air is working its way in there now to throw a lean code

 

[Fosters]

I've had a shop forget to put the oil cap back on, on my old excursion... shortly after the oil change i noticed no power and crappy mileage... no CEL. I popped the hood, saw the cap sitting on top of the headlight, put it back on, checked the oil, the thing had sucked about 3 quarts of oil through the PCV and burned them in a very short amount of time. Put oil in it, power came back (it was no longer running lean as hell), but the fuel mileage was still in the 8s, compared to the normal 12. changed the o2 sensors, mpg jumped back to 12. Never got a CEL.

 

[Mikes06GT]

It ended up being a breather cap on passenger valve cover. I was running just one breather. My bad. Good news is car is running great now.