to lean?
 

I have an 02 avalanche with K&N, condensater, and acetone with tires at 50 psi. (22mpg average at 60 mph and 24 with 55 mph and no ac). Yesterday I had it in the shop, the engine light was on. Autozone told me it was my O2 sensors on the back ( I have four L&R side 2 off header pipes and 2 behind the cats) the mechanic said I was running 25% lean on both banks. He mentioned a vacuum leak, but I have not found any nor did he. Help any ideas? It is throwing out codes but only in respect that it is lean.

how many miles are on the vehicle? a properly working o2 sensor is what is going to keep it from running to lean, a wide band (5 wire) o2 sensor can alow the engine to run leaner because it is more sensetive on the lean end of the range, but I suspect you simply have a heated o2 sensor (alowing it to start working quicker and last longer) but they will often still only last 60,000 - 80,000 miles, and that will varry on the vehicle, and how many cold starts it has gone thru.

aside from that, if it is a vaccum leak, you can often find it with a piece of rubber hose, stick one end in your ear to listen, and move the other end around the hoses coming off the intake manifold, and the gaskets of the manifold to listen for a hissing sound.

mileage
 

113K that im aware they have never been changed. Autozone ran the code and said it was the rear O2s, the mechanic just said the codes show to lean. I will try the hose idea thanks

Could just be that the rear O2s are worn out.

I would probably go with autozone more then the mechanic. Mechanics are sometimes not out for your best interest. Autozone has really nothing to lose or gain by telling you the correct infromation when running the codes. Also I congrat you for letting autozone run the codes on the car. Its something I always stress doing before going in and actually fixing the car.

haha me to, you cant fix the problem by u throwing parts at it. get the light scanned (its free! get off your lazy butt and go!!!)and they will tell you whats setting the light off.

113k miles is a bit, so im betting the 02 sensors are clogged or just plain worn out...nothign you can do to clean them either

great advice
 

Thank you for the great advice. I going to get the new sensors today.

I spray carb cleaner on gaskets/components.... If the idel jumps and/or stutters - you found a leak :thumbup:

^^^ yup^^^ works well for vaccum hoses and such.