Welp, as my truck just passed the 90k mark, I think it is time for me to replace my O2 sensors. Currently my D is running very smooth, but lately my MPG dropped dramatically. I usually can get 11-12 driving around town. Now I get like 9-10. No codes or anything. The only conclusion of my bad mpg is worned out O2 sensors? My D does seem to run more rich than normal under cold starts as I can smell rich fuel.

I'll let you guys know if this returns my MPG after changing out both my O2 sensors. Does anyone know of any other sensors to be replaced giving at 90k? I pretty much replaced all other known bad sensors such as TPS, and both tranny and speed sensors.

 

I would start off with your primary pre-cat o2 sensor since it is the one the PCM reads for adjustments... The downstream post-cat is just for cat efficiency... I wouldn't touch that one unless it starts to give codes... I cannot really think of any other sensors to change out, as like I said, they would most likely pop a code if they fail...