99 MPG in V4 when stopping

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tkdgirl

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My 2011 XL Denali just started spitting crazy fuel MPG. Starts in V8 with regular mpg but when I slow down, it turns on V4 and the mpg goes way up when stopping. The only thing different recently is using E85 to top off my tank. This morning, it was really sluggish and hard to excel between 30-55. Tonight it was fine but still had the weird mpg stuff Anyy ideas? Range AFM device will be here Saturday, thankfully.

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BG1988

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My 2011 XL Denali just started spitting crazy fuel MPG. Starts in V8 with regular mpg but when I slow down, it turns on V4 and the mpg goes way up when stopping. The only thing different recently is using E85 to top off my tank. This morning, it was really sluggish and hard to excel between 30-55. Tonight it was fine but still had the weird mpg stuff Anyy ideas? Range AFM device will be here Saturday, thankfully.

View attachment 278009
normal

It's called Deceleration fuel cut off (or DFCO)
it will take a bit for it to adjust to E85, E85 is about 105 octane..


mine will be here Friday or Saturday also :D
 
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swathdiver

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My 2011 XL Denali just started spitting crazy fuel MPG. Starts in V8 with regular mpg but when I slow down, it turns on V4 and the mpg goes way up when stopping. The only thing different recently is using E85 to top off my tank. This morning, it was really sluggish and hard to excel between 30-55. Tonight it was fine but still had the weird mpg stuff Anyy ideas? Range AFM device will be here Saturday, thankfully.

View attachment 278009

Perfectly normal for a stock tune.

How often have you been topping off with E85 and what exactly does that mean? Also, are you pumping 87 or 91/93 octane gasoline?
 
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tkdgirl

tkdgirl

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Perfectly normal for a stock tune.

How often have you been topping off with E85 and what exactly does that mean? Also, are you pumping 87 or 91/93 octane gasoline?
This was the first time since I was in an area that had E85. Not a lot around here. Otherwise it's 91+ per the manual.
 

swathdiver

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This was the first time since I was in an area that had E85. Not a lot around here. Otherwise it's 91+ per the manual.

The engines love E85, as it is basically like a race gas. You won't get the full benefits of power until you've run 3-4 consecutive tanks of it. Running it occasionally does help keep the system clean. If you run a mix you might get slightly better gas mileage and reduce your fuel bill. Mine, not a 6.2 Denali, gets its best mileage mixing 5-6 gallons of E85 and 20-21 gallons of gasoline.

If you don't already use it or something similar, download the Gas Buddy app to your phone to see where E85 and E15 is sold in your travels.

What's your favorite part of owning the Yukon XL Denali?
 
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tkdgirl

tkdgirl

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The engines love E85, as it is basically like a race gas. You won't get the full benefits of power until you've run 3-4 consecutive tanks of it. Running it occasionally does help keep the system clean. If you run a mix you might get slightly better gas mileage and reduce your fuel bill. Mine, not a 6.2 Denali, gets its best mileage mixing 5-6 gallons of E85 and 20-21 gallons of gasoline.

If you don't already use it or something similar, download the Gas Buddy app to your phone to see where E85 and E15 is sold in your travels.

What's your favorite part of owning the Yukon XL Denali?
So far, my favorite part is the power this 6.2L puts out. Drives like a dream. Looks pretty but is all business. Looking forward to towing to see how well it does. Really happy with it so far.
 
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