reduced fuel mileage

[H8 PVMT]

Those codes are both for Bank 1, one is rich and the other lean. Still getting the same codes after replacing the O2 sensor or no more code(s)?

If the original sensors weren't bad, then they were accurately reporting that the exhaust is actually rich or lean. But, maybe a sensor was bad and reporting that the exhaust was lean. So the PCM unnecessarily richened the fuel mixture which sooted up the 275K-mile cat converter and the O2 sensor. The cat was then clogged and the sensor is partially choked with soot so now it's reading the exhaust as lean... Just a guess on a plausible story.

The conflicting codes both being for Bank 1 intrigues me.

Its been a while since I pulled the codes, I could be incorrect on the exact numbers but it's plausible that the cat is clogged up. I saw it since we moved, we moved from NC to Colorado - not sure if the altitude change did anything to the truck or not. My current thought is replace the cats since that has been a constant with the issues I've had and about the only thing I haven't replaced. lol

 

[rockola1971]

Id get it up in the air and check all brakes for drag. Check rearend for bearing problems too. (axle and differential) Is there a dogleash tied to the bumper?

 

[H8 PVMT]

Id get it up in the air and check all brakes for drag. Check rearend for bearing problems too. (axle and differential) Is there a dogleash tied to the bumper?

lol no, no dog leash *runs out to check.....

 

[H8 PVMT]

Took it into Midas for a diagnostics test and it came back to be the MAF sensor wasn't working properly and the intake manifold gasket was leaking. Quote to repair, 650.00. Went to auto parts store, spent 100.00 and did it myself. SES light is off and she is running like a champ. Glad I didn't have to replace the cats, quotes for that were coming in around a grand, yikes.

 

[rockola1971]

I usually get my MAF sensors (AC Delco) off ebay. They usually run around $50-60. Leaking intake gaskets huh? Im pretty sure thats whats wrong with my Tahoe 5.3L. It only acts a fool in the cold below 40 degrees.