You guys are trying to see afr after the cat? O2 readings tend to average out and stay even after the cat when they are doing their job. But verifying against joes truck is a good test. Can't argue with doing the same test on another truck.

Well you do realize it's not a Prius right?

Interesting thread, as I have been considering replacing my 04 1500 Avalanche with a 8.1 pickup to pull our 38' PowerQuest once per year to LOTO. Maybe I will keep my Avalanche and continue to rent/borrow for the once trip/yr. Boat is slipped and winter storage is 5 miles away. I drive a company vehicle 90% of the time and can't justify payment on a new truck.

I was told after the cat woudln`t be too accurate but Joe truck got some good readings there, I`m going to look into the fuel trims.. I don`t like those air fuel numbers

My '02 2500 HD 4x4 8.1 with Allison is the same. 10-13mpg.

Does anyone know, what controls the Fuel trim? I believe the O2 sensor is what ''trim''s it back to target, but I know the ECM relies on the input from the MAF, MAP, TPS, values?

Should also be noted, the truck has a Blackbear performance tune. Mine does also, but has much more stable AFR. Like stated, I never see a deviation from 14.7 unless wot. Dan sees a deviation everytime he changes throttle position, and the ECM has to catch up, to lean it back out.

il bet the performance tuner is throwing more fuel at it but every 8.1 that i have ever seen suck fuel.maybe going back with the stock tune will help some but it will still suck fuel.i know 2 people who unloaded their trucks because they could not pass a gas station.on the other hand il bet it pulls that big cig with no problems.

Is the 454 in your truck a competent puller? Maybe I should consider one as a second vehicle for the limited amount of towing I actually do.

Actual fuel trim as shown in % from -25 to +25% is controlled directed by the front pre cat 02's. The other inputs use multipliers in the tables to determine commanded fuel amounts. The o2's just pick up how the engine is reacting to those commanded amounts and the ECM "trims" accordingly.

Get a diesel. I read on the internet, they get 24mpg empty, and 18mpg towing a 38 Top Gun. I think you can get a 2014 loaded up dually for around 65k. Or, a 2001 with 300k miles for 30k. They will go a million miles no problem, and are very cheap to repair. If going used, I recomend a 2003 Ford 6.0L, and get a tuner. Make sure you tow the cig in high performance/high boost mode. Just be sure to refill the coolant jug when you stop for fuel. What works really nice, is when the raw coolant blows out the tailpipe, it leaves a nice tack coat on the boat, for the black smoke that follows. Your boat will look like a greasy coal miner by the time you get to the ramp.. But at least your mpg will go from 7 towing, to 8, maybe 9 with a tailwind. Plus, you'll get christmas cards from the service department at the dealer, thanking you for sponsoring their annual xmas golf outing.