Very Poor Gas Mileage

mikez71 said:

I'm at 8.7MpG, use lots of E85, slightly quicker than traffic, all city, 5.3L, 3.08.
I probably need to check tire pressure.

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No, you need 3.73. Note how the 8L90 & 10L80 have even more assertive gearing than the 6L80 for getting underway.

10L80 x 3.23: ... 15.15 ... 9.66 ... 6.95 ... 5.72 ... 4.91 ... 4.13 ... 3.231 ... 2.75 ... 2.23 ... 2.07 (7.32 Spread)
8L90E x 3.23: ... 14.73 ... 9.60 .... 6.72 .... 5.46 . . . . . . . 4.10 ... 3.231 ... 2.75 . . . . . . . 2.10 (7.01 Spread)

6L90E x 3.08: . . . . . 12.41 . . . . 7.28 . . . . . . . . . 4.72 . . . . 3.55 . . . . . . . 2.625 . . . . . . 2.05 (6.01 Spread)
6L90E x 3.73: ... 15.03 . . . . 8.82 . . . . . . 5.71 . . . . . . 4.30 . . . . 3.18 . . . . . . 2.49 (6.01 Spread)

If your use case had enough highway mileage, one might recommend 3.42.

AmunRoo said:

Yukon has the L92 and the Escalade has the L94 with AFM.
I was under the assumption that I would have better gas mileage since it automatically switches between four and eight cylinders
but I guess that's all just hokum and fairy tales LOL as far as calculating gas mileage.
I wasn't running off what the dummy screen tells me.

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Engine Half@$$ was made primarily to benefit GM during their Corporate Average Fuel Economy testing.
On a brand new vehicle, sure, this is worth 2 or 3 highway MpG.
Bet if they did this testing after 100,000 miles, they'd find the MpG benefit fades over time.
And this is all before the two mode lifters quit.
You may want to look into at least disabling the Engine Half@$$ featurebug.
An ecm / tcm tune would likely get back the MpGs, plus make it more fun to drive.

AmunRoo said:

Once I'm down to about an eighth of a tank, it only fills up with about 15 to 16 gallons,
which does lead me to believe that there is an issue with the floater.

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More likely an issue with the Evaporative Canister Purge system.
Do either of your vehicles 'fart' - push out vapors - when you unscrew the cap?

No farting! They are both proper ladies lmao

I did however notice that the AC compressor is constantly cycling even though I'm not running AC. I'm going to turn off HVAC completely and see if it's still cycling.

AmunRoo said:

Once I'm down to about an eighth of a tank, it only fills up with about 15 to 16 gallons which does lead me to believe that there is an issue with the floater.

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How many miles does it take you to get down to 1/8 of a tank in your Escalade? What does that equate to for miles per gallon when you fill it up with 15-16 gallons? How does this compare to your Yukon?

Before you buy anymore parts, do this one simple thing because it sounds like it until now you’ve been mainly operating under guesses and assumptions instead of actual diagnostics.

So, you are measuring/estimating fuel consumption based upon the 'position' of your gas gauge? If yes, that could be contributing to your issue, as these gas gauges are not linear across their bandwidth, and each individual gauge may vary some others. I recommend, if you have not already done so, measure your fuel consumption based upon how much gas you put into the truck until the first automatic gas pump click-off and the actual miles driven.

6spd 2012 yukon xl 6.2l 3.42 awd (average 9.6mpg) *even after extended highway driving for hours without stopping
6spd 2018 silverado crew cab long bed 5.3l 3.08 4X4 (average 9.5mpg)
6spd 2016 suburban 5.3l 3.08 2wd (average 9.5mpg)

explain that one to me lol
I know why-my big ass foot!

4spd got about the same in my 2000 yukon xl 5.3l 3.42 4x4
4spd got about the same in my 2003 silverado 5.3l 3.72 2wd extended cab, long bed
4spd and about the same in a couple other 2wd suburbans 5.3l 2004,2005

my wife loves to comment on it about how she brought mine up to 13 and I made her's go down

one would think the different weight and axles ratios, engine size, etc would make one better or worse than the other but NOPE
when I went to the 6.2l, from a 5.3l I was kinda scared I was going to get like 8, but that never happened. I mean I can make it happen but that's a workout.

My current average

AmunRoo said:

My current average

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When was the last time you reset that?

You still need to do the old school calculation as the dash uses information from the sending unit. If the sending unit is off, the dash calculation can be off.

Fill tank (stop at first click of pump), note starting mileage on odometer, drive until you need to refill, note ending mileage on odometer, fill tank (stop at first click of pump), note gallons pumped, divide miles traveled by gallons pumped.

check to make sure your speedo is right too. if someone put taller tires on it. the milage is wrong too

I'm definitely going to try and remember to do the manual calculations for the gas mileage lol

I just bought new rims and tires. Running 24s now