2012 Yukon Denali 6.2. Poor gas mileage, no codes thrown and no check engine light

[petethepug]

You can’t change the milage but you can change the driving behavior or the fuel. For me it’s easiest to run e85 vs changing the driving behavior.



$104.30 vs $180.09 for 91. Now that the fuel & evap system has been refreshed, the tank will hold a healthy 31.6 gal of fuel. Prior to that I could only get 26 gal in on a bone dry tank. The DIC accurately showed I had 15 miles of fuel left.

 

[B-train]

Will your scan tool reset the alcohol monitor? I wonder if it's stuck on a setting for e-85 and dumping fuel in.

 

[j91z28d1]

Will your scan tool reset the alcohol monitor? I wonder if it's stuck on a setting for e-85 and dumping fuel in.

I always forget about that with these trucks.

do you know what it's under on a tech 2? I'm curious to see if mine has a reading.

 

[j91z28d1]

You can’t change the milage but you can change the driving behavior or the fuel. For me it’s easiest to run e85 vs changing the driving behavior.

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$104.30 vs $180.09 for 91. Now that the fuel & evap system has been refreshed, the tank will hold a healthy 31.6 gal of fuel. Prior to that I could only get 26 gal in on a bone dry tank. The DIC accurately showed I had 15 miles of fuel left.

thats interesting pricing. I stopped for fuel yesterday, 87 is 3.49 I think it was, 93 at 4$ and e85 was 3.00$

kinda. interesting e83 is about the same as you but the gas is much higher.

it feels like a scam all the time haha.

 

[Fless]

I always forget about that with these trucks.

do you know what it's under on a tech 2? I'm curious to see if mine has a reading.

On the menus for my '04 the alcohol content is under the Engine Data 2 menu.

 

[j91z28d1]

On the menus for my '04 the alcohol content is under the Engine Data 2 menu.

I'll looking around in there tonight.

there's been a bit of debate over the years of the hybrid can use e85. all the marketing brochures list this Gen as flex, but the cap isn't yellow. I'd bet it has all the same fuel pumps and lines thou. in hp tuners there is alcohol tables and they are populated.

a e % reading would lead to yes, but I have meant to research injector sizing in these trucks, usually the flex has bigger injectors.


sorry to hi jack the thread, but yes I've seen a few threads about e% being off and needing reset in the trucks that are flex but don't have an actual sensor. something for the op to check forsure

 

[swathdiver]

While sitting in the truck at idle I can watch the computer display "Average fuel mileage" it starts dropping while just sitting there. 1/4 tank of gas in it. The computer started at 8.2mpg which is low and in about 15 minutes the computer read 6.9 mpg. My wife is complaining that this truck is using too much gas. This truck has the 6.2 flex engine and normally around town its about 14mpg and thats what the display shows.

I own a very good active scan tool that allows me to check and activate most things on this truck.

No check engine light. No codes are shown. No misfires on any cylinder. I removed and cleaned the MAF sensor and the scan tool shows it functioning.

I do not smell any fuel while I'm under the truck and don't see any fuel leaking.

About 3 months ago I had to replace the Fuel pump, EVAP canister, EVAP Solenoid and purge valve.

Does something have to be reset so this system gets better gas mileage? ECU?

6.2s are very efficient engines for what they are. They burn about a gallon an hour idling. The 5.3 burns about .78 gallons per hour idling.

If you run through a tank of slow speed city driving, where your average speed was below 22 mph, she will have used fuel at a rate of 1.5 gallons per hour versus 1.3 GPH for a 5.3.

Using the data from your DIC during refueling you can calculate how the engine is performing against how it's being used.

The data in green comes from the gas pump and my DIC. Excel is then used to make automatic calculations some of which are shown to the right.


When we're driving in the city, the truck will go 12-15 hours before requiring fuel again. Out on the highway she can run for about 8 hours before requiring fuel while still having a healthy reserve.

More important, and tell your wife this, you know how many people have died in a full length Yukon XL 4x4 or AWD since 2009? None. Not since I checked last anyway with the IIHS.

We had a guy join this forum a few years back, he lived and worked in downtown Miami and was frustrated with his 6.2 Tahoe, it barely got 10 mpg on a tank of gas. We finally convinced him to go eat a hamburger in Belle Glade, 85 miles away, and he quit complaining about it.

 

[swathdiver]

I don't understand why the computer would display the AVG mpg declining while the truck is sitting still?

Because it is. As time goes on, the average speed decreases and therefore the fuel efficiency does as well. It's a math equation or should I say, multiple equations.

On a GMT900, the alcohol content is found under the "Fuel Trims" menu.

 

[vcode]

Because it is. As time goes on, the average speed decreases and therefore the fuel efficiency does as well. It's a math equation or should I say, multiple equations.

On a GMT900, the alcohol content is found under the "Fuel Trims" menu.

Yep, reset it while you are idling and it will read 0.0mpg until you are moving!

 

[Chris Mosher]

Smell your oil, does it smell like gas? If so, your engine doesn’t like idling very long. I replaced O2’s, plugs/wires, MAF and PCV’s and problem went away.