25.8 MPG! 2016 GMC Sierra ROUND TRIP - 463.9 miles

[JB45]

6 minutes ago, KARNUT said:

It was summertime, I didn’t see much difference in the winter. Mine was a 5.3, 342 gear, 20 inch factory wheels and 0-20 factory spec oil. I did lots of testing was cylinder deactivation on and off with no real change. I used hypertec hand held to turn off cylinder deactivation among other adjustments.

Alright good to know. Not expecting a 10 mpg increase from oil but just wanting to eliminate any potentials. Not sure why the stealership put 5w-30 in it to begin with. I haven't looked into the hypertec. I'm thinking about using HP tuners to turn off cylinder deactivation, I know that you can also use it to make a custom tune for the ECM/TCM but that is outside of my abilities. So I'm really wanting to get it on a dyno and have everything professionally done. Just very wary of who I'm going to let do it. 

[Grumpy Bear]

2 hours ago, JB45 said:

Yes I understand that, but I actually got 1 mpg better the tank running 80 than 70, that's why I added that. I've read about guys with leveling kits and 33s getting 18, running 70. That's why it's suprising that even when driving easy(70 mph max interstate) I can't break 15.5 with a bone stock, AFM, no tune, etc. This is with multiple tanks, driving the same long interstate commute. I didn't notice much difference between 70 or 80 mph tanks. I'm not expecting 25 mpg, that takes patience and dedication. Just seeing if anyone else has this

  AFM is a load based program. At 80 mph it is almost never on UNLESS you have a strong tailwind OR your running down hill. AFM isn't magic, it's a device. 

[amxguy1970]

14 hours ago, SouthwestORV said:

That’s the key! I never set the cruise higher than 60mph. Funny thing is...you don’t really get where you’re going much faster at 65mph, or even 70mph. I’ve noticed that mph and throttle input make a huge diff on these trucks! 
These wheels were the cheapest rim offered by Discount Tire for this pickup, then I put a one size up from stock Cooper highway tire on there. I love how it turned out. Still very good road manners. 

That is some restraint, I am not a speeder but 60 here in Texas can't do it. Basic math says otherwise in terms of getting somewhere faster. All depends on the length of the trip but for a 230 mile drive the difference between 70 and 80 is about 30 minutes or around 17% time savings. I can finish lunch at a sit down fast food place by then... When we drove to New Mexico even going 5 mph slower is about an hour difference over 630 miles. Granted I weigh the time and gas mileage and see what I feel or need to do. If I am pressed for time I will sacrifice mpg to make sure I get to my destination a little early or on time, if I have nothing but time I will set cruise at the speed limit and save some mpg, either way you do arrive faster going faster (unless you get pulled over). 

2 hours ago, JB45 said:

Yes I understand that, but I actually got 1 mpg better the tank running 80 than 70, that's why I added that. I've read about guys with leveling kits and 33s getting 18, running 70. That's why it's suprising that even when driving easy(70 mph max interstate) I can't break 15.5 with a bone stock, AFM, no tune, etc. This is with multiple tanks, driving the same long interstate commute. I didn't notice much difference between 70 or 80 mph tanks. I'm not expecting 25 mpg, that takes patience and dedication. Just seeing if anyone else has this

Must have had some very weird scenarios that caused that because apples to apples (no wind, same road) that is not happening, physics won't let it. 

2 hours ago, JB45 said:

That's awesome. That's what I was hoping for. At this point I see no reason to keep the AFM, it drives me nuts and it's obviously not helping my fuel economy. Plus I'd like to do an engine and TCM tune because I don't really like the way it shifts and feels like there is plenty of horsepower there when torque management and whatnot isn't in the way. Did you run 0w-20 oil? And did you notice a significant drop in mpgs during cold weather? I'm from Missouri so it's not like the Frozen North or anything but it's been in the 20-30s and that's when I was getting 14. 

Yours must be broken or in a very unique scenario that allows for better mpg at 80 and AFM not helping fuel economy. You aren't noticing a couple tenths when averaged out over the tank but tests show about 4 to 10 percent in savings over non AFM engines. There is a reason so many manufacturers are putting those on cars as well as stop start, they save fuel and the more they operate at their peak efficiency the more they save. If you aren't at those peaks very often you won't see much impact but that doesn't mean they aren't there saving fuel... Not to mention you have to constantly be looking at when and when it isn't working otherwise you have no idea how little or often it actually turns on. I know just wanting my DIC the mpg jumps up a couple when it turns on.

 

Tyler 

[JB45]

22 minutes ago, Grumpy Bear said:

  AFM is a load based program. At 80 mph it is almost never on UNLESS you have a strong tailwind OR your running down hill. AFM isn't magic, it's a device. 

This is what I said in my first post as one of my thoughts;

 

"Coming back from the 5hr trip I actually ran 80 so I spent less time in AFM mode. This was the time frame which I got 15.5"

 

That's what I was getting at, at 80mph I wasnt in AFM mode and was getting better mileage. Thanks for the sarcastic response but next time please read the post in it's entirety. 

[Grumpy Bear]

8 minutes ago, amxguy1970 said:

 

Yours must be broken or in a very unique scenario that allows for better mpg at 80 and AFM not helping fuel economy. You aren't noticing a couple tenths when averaged out over the tank but tests show about 4 to 10 percent in savings over non AFM engines. There is a reason so many manufacturers are putting those on cars as well as stop start, they save fuel and the more they operate at their peak efficiency the more they save. If you aren't at those peaks very often you won't see much impact but that doesn't mean they aren't there saving fuel... Not to mention you have to constantly be looking at when and when it isn't working otherwise you have no idea how little or often it actually turns on. I know just wanting my DIC the mpg jumps up a couple when it turns on.

 

Tyler 

Yep. Well said! 

 

Anyone that reads my drivel knows I've made an art out of keeping that AFM active. I can vouch for 10% +  if you maximize it's use. I can also vouch that when loaded until it doesn't work...well....it doesn't work. 

 

EPA window sticker on Pepper said 24 mpg highway. I just finished the summer of 2019 at 30.2 mpg, 25% better with it active. Yes I drive the EPA 55 mph 90% of the time and am about 99% highway miles. 

[JB45]

14 minutes ago, amxguy1970 said:

That is some restraint, I am not a speeder but 60 here in Texas can't do it. Basic math says otherwise in terms of getting somewhere faster. All depends on the length of the trip but for a 230 mile drive the difference between 70 and 80 is about 30 minutes or around 17% time savings. I can finish lunch at a sit down fast food place by then... When we drove to New Mexico even going 5 mph slower is about an hour difference over 630 miles. Granted I weigh the time and gas mileage and see what I feel or need to do. If I am pressed for time I will sacrifice mpg to make sure I get to my destination a little early or on time, if I have nothing but time I will set cruise at the speed limit and save some mpg, either way you do arrive faster going faster (unless you get pulled over). 

Must have had some very weird scenarios that caused that because apples to apples (no wind, same road) that is not happening, physics won't let it. 

Yours must be broken or in a very unique scenario that allows for better mpg at 80 and AFM not helping fuel economy. You aren't noticing a couple tenths when averaged out over the tank but tests show about 4 to 10 percent in savings over non AFM engines. There is a reason so many manufacturers are putting those on cars as well as stop start, they save fuel and the more they operate at their peak efficiency the more they save. If you aren't at those peaks very often you won't see much impact but that doesn't mean they aren't there saving fuel... Not to mention you have to constantly be looking at when and when it isn't working otherwise you have no idea how little or often it actually turns on. I know just wanting my DIC the mpg jumps up a couple when it turns on.

 

Tyler 

I was traveling on I-44 which isn't a mountain pass but its definitely not Kansas. First trip was in nasty storm, second in ideal conditions. Either way, I'm getting 15.5 mpg no matter how I drive. Slow take offs, 70mph cruising, etc or normal driving cruising 75-80. There's plenty of other guys with basically the same truck, ones who even commented that were getting 24mpg driving "roughly" the same. Karnut even did tests with and without AFM with not much changes. I would agree with you that AFM undoubtedly has to work if you drove like the OP, on pretty flat roads. But when you are in and out of hills, in and out of cylinder deactivation, I'm not seeing the benefits in my application. 

[SouthwestORV]

14 hours ago, JB45 said:

So I've got a 2015 GMC Sierra 5.3 4x4, double cab, 6.5 bed stock wheels and tires no lift. When I first got the truck, went on a 5 hour interstate trip running 70-75. It was cold and rainy and I only got 14 mpg. Very disappointed since it's advertised for 22. Now after about a week of grandma driving I've graduated to 15.5 mainly highway. I've calculated it manually btw. What's the deal? I don't expect to get 20-22 but would be happy with 18. Here's my thoughts. 

 

It's warmed up in the 40s where I live the last couple days.

 

Coming back from the 5hr trip I actually ran 80 so I spent less time in AFM mode. This was the time frame which I got 15.5

 

From the dealership it had a fresh 5w-30 oil change, seriously planning on going to 0w-20, like the manufacturer intended. 

 

My rear tires are 30psi, so probably going to top them off tomorrow while changing my oil. 

 

Is this enough to make me get that bad of fuel mileage? Thoughts, what are you guys doing to get even 18? And please try to keep it specific to the GenV 5.3 ecotec. If your throttle body 350 got 17 one time that's great but doesn't really relate. Lol.  

 

I would expect better too...hmm. Several thoughts, based on personal experience:

1. I'm running 91 Octane fuel. You?

2. I run my tires above 34psi = less rolling resistance. 

3. I've noticed that the fuel economy drops drastically as speed increases. At 75mph my truck is getting about 21mpg.

4. Yes, my truck is 2wd so there is less weight, and less energy loss because it isn't turning/hauling all of the 4wd components.

5. My truck is also lighter because it's a regular cab, even if the wheelbase is similar. 

6. I do run 0w-20 Mobile 1 Synthetic oil in the truck, and follow the recommended service intervals on the display. 

7. Running the way I do, my truck spends a LOT of time in "V4" mode. Yet, only the slightest throttle increase bumps it back to V8. So I imagine the larger/heavier all season tires on your truck, plus the added weight and parasitic losses from 4wd simply require more effort to haul around.    

[Grumpy Bear]

4 minutes ago, JB45 said:

This is what I said in my first post as one of my thoughts;

 

"Coming back from the 5hr trip I actually ran 80 so I spent less time in AFM mode. This was the time frame which I got 15.5"

 

That's what I was getting at, at 80mph I wasnt in AFM mode and was getting better mileage. Thanks for the sarcastic response but next time please read the post in it's entirety. 

I wasn't being sarcastic. Your basis of comparison was 70 mph and it isn't anymore active at that speed. It can't be less active than zero. That not sarcasm. That's a fact. This systems sweet spot is 50-55 mph. IF you see it come on at 70 mph bet you have a downhill and fuel is zero. I has no effect. At speeds such as your driving it can't help you. Not won't, can't. 

 

3 minutes ago, JB45 said:

 There's plenty of other guys with basically the same truck, ones who even commented that were getting 24mpg driving "roughly" the same. Karnut even did tests with and without AFM with not much changes. I would agree with you that AFM undoubtedly has to work if you drove like the OP, on pretty flat roads. But when you are in and out of hills, in and out of cylinder deactivation, I'm not seeing the benefits in my application. 

 Yea.... they might make those comments but I'll take their money. 

 

KARNUT is not a speed freak but he isn't bashful either. He drives above the systems optimal limit enough that it doesn't have much effect. So what he is saying is the "Within the references of his personal driving style" he doesn't see much difference.  

 

BINGO!

[SouthwestORV]

4 hours ago, L86 All Terrain said:

Great mileage, well spec'd truck to be a hyper mile'r. Personally I cant drive that slow. I get about 16mpg with my 6.2L on a 500mi trip. I do the 250 mi (one way) drive in 3.5-3.75hrs at 67mph passing everyone I catch as soon as safely possible. If I drove the limit of 55 (averaging lower than 55 because of slow traffic) and didn't pass anyone it's easily a 4.5hr drive and I'd be lucky to get 19mpg with my tires, so the cost of time is more valuable than $10-15 in gas when I am on my own leisure time as I don't get much of it. Two-way traffic and one lane makes a huge difference in commute times. You wont notice it on your wonderful concrete multilane freeways of the USA. Stock tires my computer would tell me 23 was my best, but now 16mpg on a day to day in the summer, I can live with that for 420hp and 33's. Don't worry about saving $10 in gas and taking an extra half an hour when your boss is paying you $30 an hour, your losing money for your company. 

If I were in your shoes I'd do exactly the same. As soon as I'm in a lifted 4x4 truck with big horsepower I flip the switch in my head to "go-mode."  I have to say, even this little 5.3 kicks tail. Lots of power for such a light pickup. My bosses both have brand new Duramax 2500HD pickups and I can beat them in a drag race from 0-top speed (we have chunks of "Mexico" around here where it's legal). That's not towing of course! These are zippy little trucks.  

[SouthwestORV]

3 hours ago, JB45 said:

Yes I understand that, but I actually got 1 mpg better the tank running 80 than 70, that's why I added that. I've read about guys with leveling kits and 33s getting 18, running 70. That's why it's suprising that even when driving easy(70 mph max interstate) I can't break 15.5 with a bone stock, AFM, no tune, etc. This is with multiple tanks, driving the same long interstate commute. I didn't notice much difference between 70 or 80 mph tanks. I'm not expecting 25 mpg, that takes patience and dedication. Just seeing if anyone else has this

It is funny that you got better MPG going 80 than 70 - I wonder what the factor was - could have been headwind. I agree that you should be getting better. I work with a plumber that drives the very truck you own, and he said he gets 18mpg on the road (with his plumbers racks, etc.) 

[L86 All Terrain]

3 minutes ago, SouthwestORV said:

These are zippy little trucks.  

For sure. Especially in Regular cab trim. I have a reg cab 2500 6L and its an absolute power animal, my crew cab 6L on the other hand is a big slug. 

[SouthwestORV]

3 hours ago, KARNUT said:

With my 14 GMC 22MPG was the rule at 72 MPH. Avoiding a traffic problem driving on a secondary road at 60 MPH for a decent amount of miles I got 24 MPG. That was with a tune and cylinder deactivation turned off.

Sounds about right - in line with what I see. 

[SouthwestORV]

48 minutes ago, amxguy1970 said:

"That is some restraint, I am not a speeder but 60 here in Texas can't do it. Basic math says otherwise in terms of getting somewhere faster. All depends on the length of the trip but for a 230 mile drive the difference between 70 and 80 is about 30 minutes or around 17% time savings. I can finish lunch at a sit down fast food place by then... When we drove to New Mexico even going 5 mph slower is about an hour difference over 630 miles. Granted I weigh the time and gas mileage and see what I feel or need to do. If I am pressed for time I will sacrifice mpg to make sure I get to my destination a little early or on time, if I have nothing but time I will set cruise at the speed limit and save some mpg, either way you do arrive faster going faster (unless you get pulled over)."

I'm the same when it comes to work Mon-Friday. I've got things to do, deadlines to make, meetings to attend, bids to submit, and the bosses even say they'll cover tickets because I'm efficient. I zip around at the limits (which is 105mph on flat, 106 downhill). But when the weekend comes, I relax and enjoy - total opposite. I have noticed over the years that on a vacation, cruising down the freeway, you'll pass tons of vehicles that are going 5-15 mph slower than you. Then you stop for fuel and restroom break, and during that time most of them pass you! If you take time to order food, they ALL pass you! Just perspective, sometimes 30 minutes isn't worth all the hurry and added danger - because if you're talking facts, physics demand that the potential for disaster increases perfectly in relation to velocity. The difference between 75mph, and 85mph can be life and death when things go wrong.  

 

Tyler 

 

[SouthwestORV]

39 minutes ago, Grumpy Bear said:

Yep. Well said! 

 

Anyone that reads my drivel knows I've made an art out of keeping that AFM active. I can vouch for 10% +  if you maximize it's use. I can also vouch that when loaded until it doesn't work...well....it doesn't work. 

 

EPA window sticker on Pepper said 24 mpg highway. I just finished the summer of 2019 at 30.2 mpg, 25% better with it active. Yes I drive the EPA 55 mph 90% of the time and am about 99% highway miles. 

I believe it! Last September I drove from Marysvale Utah to Taylor, AZ with a dirt bike in the bed of my 2016 Sierra 5.3. It was a Sunday morning, so I took my sweet time and cruised 55mph the entire way. By the time I hit Page it said 30MPG! When I filled up in Page the "distance to empty" said "999 miles". When I calculated manually, I was in fact doing 30mpg. But I rarely share that experience because people roll their eyes. 

[SouthwestORV]

34 minutes ago, JB45 said:

I was traveling on I-44 which isn't a mountain pass but its definitely not Kansas. First trip was in nasty storm, second in ideal conditions. Either way, I'm getting 15.5 mpg no matter how I drive. Slow take offs, 70mph cruising, etc or normal driving cruising 75-80. There's plenty of other guys with basically the same truck, ones who even commented that were getting 24mpg driving "roughly" the same. Karnut even did tests with and without AFM with not much changes. I would agree with you that AFM undoubtedly has to work if you drove like the OP, on pretty flat roads. But when you are in and out of hills, in and out of cylinder deactivation, I'm not seeing the benefits in my application. 

Let it be known, I started my drive (original post) at 5800 ft elevation, climbed to over 6000ft, and arrived at my destination at 2300ft. Then drove home and climbed all the way back up above 6000 ft on hills and canyons, then back down to 5800 ft. This is a very twisty, curvy up and down road, two lanes at that for most of the drive. HWY 77 in Arizona.