Mpg display different from trip 1 avg to general avg?

So since I've purchased this denali, I've seen mpg from regular 87 for 3 whole tanks and switched to just premium 91 for 4 tanks..
On the instrument cluster, you have your avg mpg and your trip 1 'personal' avg mpg... one says 14.6 on the regular display, and my trip 1 avg says 16.7... I always reset both so i can do the math at the pump ( miles driven divided by gallons pumped) and it's in the middle of both of these numbers..

I have the convenience of having a set schedule and drive pattern so my driving habits don't change much at all, giving me a good idea on the difference regular vs premium...

But my main question , is why are the 2 avg different? They are on the same miles driven reset at the same time....

I noticed premium gave me roughly 1.5 better mpg overall on the tank, as I went from 13.6 to plus 15 most tanks... but my trip 1 ways says 16.Something and never matches the first avg
...

So I decided to just run premium, tanks costing roughly $6-7 more, but get 1.5 better mpg per... 30 gallons x1.5 mpg = 45 miles= 3 gallons of fuel @2.29/gallon for premium where I live (thank you gas buddy app).. 3 x2.29= $6.87

Almost no difference in cost, and it feels more awake, could be placebo effect but give me my dream!!!lolz

And in the end, my argument with my friends about premium is this... I get premium gas that's great for my motor, and I give up 2 micro brews for domestics at the bar, one night, and I made my money back... it's amazing how my friends look me when I tell them I run premium in a truck...

But I let my friend borrow my truck, came back t the end of the day and said, " dude your truck is the shit, it felt like I was in a freshly detailed vehicle and it scoots too".. I said " you WERE in a freshly detailed vehicle!!! And no food in the truck kids!!!hahahahh

But back to the main question... why are the avgs different? Any ideas or thoughts?

As far as the MPG goes, the average tank resets every time you reset the trip meter, while the overall average only resets if you manually reset it (which you can do with the steering wheel buttons.) So the difference may have something to do with how often you reset. Try resetting them both and see if they stay the same, they should.

As for the fuel, I know this is a heated topic on the Intertoobz but unless your 6.0 is a high compression engine that pings on regular fuel you get zero benefit from running high octane fuel and you're just throwing money away by running high octane.

Octane = resistance to spontaneous combustion. High octane fuel actually contains less energy per gallon than low octane fuel so, again, unless your truck pings on low octane, you will usually get better MPG with low octane than with high.

As a side note, many people who run high octane also insist on "no ethanol." Want to guess what the octane of pure ethanol is? It's something like 100 or 115. Ethanol is actually an octane BOOSTER.

The more I've been reading, premium in my motor doesnt do squat. I did notice it idles smoother and has a little more pep under normal driving conditions, but it seems like I'm just over the top right now since it's new to me and premium is only 2.29 right now.. lolz

And for the cluster, I reset both at the same time, trip one avg and main display avg, and keep trip 2 for oil miles. But they are reading different numbers, I just filled up 2 days ago, and the wife wanted to take the truck, put 120 miles on, and it reads 15.3 on the main display, but 16.4 on the trip 1...

I don't know, it's no big deal, I thought someone might have had a technical answer.

I guess when I get my tune it will be an 87 tune, so I'm not committed to premium, even though I'll probably still get it..hahahaha

It's only 6 buck difference, that's one less 1 grey goose/tonic at the bar.

D is for DENALI said:

It's only 6 buck difference, that's one less 1 grey goose/tonic at the bar.

Click to expand...

I look at it this way: If I saw $6 laying on the ground, I wouldn't walk past it. So to me if I can save $6 I will.

Fully understand.

Again, I'll most likely get the 87 tune l, but for now so far my mpg has gone along with my math at the pump(miles÷gallons)...

I very well could be wrong, but that's why ive been keeping track myself outside of trusting the gauge.


87 i would avg 13.8 and 91 I get over 15, sometimes 16, depends who is doing the driving..lol

I'm not worried about 6 bucks every 2 weeks. That's 43 cents a day. I'll manage. that is taking only into account that I'm not making a single gain from running 91, which so far, I am. Maybe when I get my tune he'll slap me right back into 87 land where i belong.

I run premium in my riding lawnmower and weepwhipper, I run vp race fuel for my rm 250.. maybe I'm a gas snob and didn't know it!!! Hahahhahahha

That's interesting...
All the octane related info i could find on this forum and others basically say:
early generation denalis 01-03 (LQ4) can run either 87 or 91 - The engine will actually adjust timing depending on octane. 91 should give a little better perf
later generation (LQ9) are higher compression and therefore require 91

01ssreda4 said:

You have a low and high octane timing curve in your PCM. It will select which is appropriate based on what fuel you are using (the combustion cycles)....so either if fine. Also, the tow haul mode will 1. increase line pressure during shifts, 2. delay shifts for more high rpm operation, and 3. delay torque converter engagement to prevent engine lugging due to extra load. These parameters are coded into the PCM but can be changed with software like HPTuners.

Click to expand...

so which is it?

Now we are getting somewhere!!

I had read from tuner threads about having 2 maps In The pcm, so you could run a general map then you could modify the tow/haul button to accommodate another separate mapping, for what I'm not sure...

But if the copied post you put in is the truth, then maybe my idle and 0-50 being smoother and better is not placebo..

Just filled up yesterday... my avgs on the cluster were both the same (finally!!!) at 15.4, and my separate math at the pump was at 15.5, so maybe it was just a fluke...

That copied post definitely raises eyebrows and possibly more discussion.

Can you send the link to that thread post so i can read it please??

Can't believe your gas prices. In Canada we're at $1.23 per liter for 87 ($4.67 gallon), 93 which is our highest grade costs like $1.50-60 per liter ($5.78 gallon). So a premium fill ends up being extra $20/tank not worth it to me but if its $2 where you are go for it man lol

Luckily it's the cheapest by my house, 2.29, just went up to 2.39 day after my fill up... in the city it's 2.50, and regular 87 is 1.89-2.05 depending where you are... yea we have cheap gas in these here hills!!! Hahhaha

Definitely download the gas buddy app, awesome way to keep up with gas prices and find the cheapest.

D is for DENALI said:

Now we are getting somewhere!!

I had read from tuner threads about having 2 maps In The pcm, so you could run a general map then you could modify the tow/haul button to accommodate another separate mapping, for what I'm not sure...

But if the copied post you put in is the truth, then maybe my idle and 0-50 being smoother and better is not placebo..

Just filled up yesterday... my avgs on the cluster were both the same (finally!!!) at 15.4, and my separate math at the pump was at 15.5, so maybe it was just a fluke...

That copied post definitely raises eyebrows and possibly more discussion.

Can you send the link to that thread post so i can read it please??

Click to expand...

there isnt much more info there above what i posted but chckout page 2 i think.
http://www.tahoeyukonforum.com/threads/new-denali-owner-few-questions.88589/page-3#post-1112875
just remember there is a lot of armchair mechanics on the forums so do your own research.

when i spoke directly to blackbear they confirmed above.