Active Fuel Management control

It would be nice to adjust the active fuel management control ourselves. Do I really need to be in V8 mode at a stop light? The only time mine goes to 4 is when I am going downhill with my foot off the gas. I remember in the old vettes they had a velet mode, economy mode and performance mode. Would be nice to have the same sort of thing on the Tahoe.

Yeah, you definitely need to be in 8 cylinder mode at a stop light (think about it).

The old ZR1 Corvette had a "Valet" mode that simply locked out the secondary intake track so the dipshit parking your Vette didn't turn your $400 Goodyear Gatorbacks into rubber pellets.

quote:

ORIGINAL: ZX1100F1

Yeah, you definitely need to be in 8 cylinder mode at a stop light (think about it).

The old ZR1 Corvette had a "Valet" mode that simply locked out the secondary intake track so the dipshit parking your Vette didn't turn your $400 Goodyear Gatorbacks into rubber pellets.

I think I remember the ZR1 having 3 modes.

I just think the Tahoe runs in 8 mode a little too much. I guess I'm just kinda pissed that auto manufacturers get away with the 17/22 MPG when I haven't seen anything over 14 with a feather foot.

I have owned a couple of ZR1's and I assure you that the valet power access system had two modes "Full Power" and "Valet".

The auto manufacturers aren't “getting away with 17/22 MPG”, they aren't the ones that calculate those numbers, it's the Government (the EPA) that arrives at these figures in the lab.

The Active Fuel Management System is not designed or intended to get that big Tahoe down the highway at 70mph on 4 cylinders.
The system was designed to cut half the cylinders during conditions requiring low power, such as coasting down a grade or slowing to a stop, under certain conditions it can activate while cruising steady at lower speeds (35-45mph), in testing it saves about 1mpg on average and that is exactly how it is advertised.
When you take the collective 1mpg savings and times it by the number of units to be sold that is a pretty decent savings, but certainly not life altering.

While I agree that the EPA generates the numbers, Chevy literature and website both unequivocally state that the vehicle will operate in V4 mode on level roads at cruising speed. My definition of cruising speed would be at least 60 mph. Doesn't matter though because I don't see V4 mode on level road at 35-40 mph unless in tow/haul mode which I think inhibits torque convertor lockup as rpm is about 300 higher.

Active Fuel Management should switch the engine into V4 mode when driving at highway speeds on a level surface and even on a very slight incline. All the literature states this and there is no technical reason that it cannot do this other than GM CHOOSING to not allow it.

Currently, there is a long thread on another forum discussing the AFM problem and some testing utlizing varios rear axels and driving modes. It appears that the 4.11 rear end will allow AFM to engage more often then the 3.43 and if ou have the 3,4 you can make it engage more if you run with the towing feature on at speeds from 30-50 mph. Based on all the testing that people have done and all the litrature that has been written by GM and the 'experts'on AFM, there is a major action taking pace by 07 Tahoe owners. Please read below:

ALL 07 TAHOE OWNERS ARE URGED TO CONTACT GM AT 1-800-222-1020 OPEN A COMPLAINT THAT THE ACTIVE FUEL MANAGEMENT IS NOT SWITCHING INTO V4 MODE AS ADVERTISED.

It is critical that all 07 owners make this call. WIthout a large call volume, GM does not take these kinds of problems seriously.

IF YOU WANT TO START RECOGNIZING THE FUEL SAVINGS WITH YOUR TAHOE, PLEASE CALL TODAY AND DEMAND GM TAKE ACTION!

There are always those that are not pleased with anything.

For a descriptive and accurate account of what active fuel management is designed to do this is a good source of info: http://www.gm.com/company/gmability/adv_tech/100_news/afm_120605.html

GM makes no claim as to what speed the AFM will or will not activate, “highway” and Interstate speeds are not the same and common sense would dictate that lower gear ratios (such as 4.10’s) would lessen the load on the engine that’s exactly what they are designed to do.

The AFM system is designed to enhance fuel economy by 6-12% on average (about 1 mpg); the software mapping for the AFM was written to allow engagement as often as possible based on engine load, if the system engaged more often the end result would be an inability to maintain speed and a decrease in fuel efficiency.

Repeated calls to GM customer assistance is not going to accomplish anything, if you wanted a 4 cylinder than you should have bought one.

Ok well i guess it is time for me to jump into this argument.....I am a salesmen at a dealership in NC, i bought a new 07 ltz and love the truck, and it is mostly all i sell. But i had a 02, and 05 both of them 4wd and i got 16.7 on the lie-o-meter, living at the same house, and driving the same roads and speeds to work.....I now have a fully broke in 07, and I get 15.3 on the meter. THE FUEL ECONOMY IS WORSE. All the literature the dealers get promise great things about dod/afm, but i will tell you now Mr. ZX1100F1, IT DOES NOT WORK AS IT IS MARKETED!!!!!!!!!!!!!! You can on average take 10% off the hwy mpg number and that will be most cars averages. NO ONE IS EVEN GETTIN THE ALLEDGED CITY MPG!!!! Granted people do not buy these for great gas milage, nor do i tell them they will get it...i tell them once you have broken in a 2wd you will average around 16.5, 4wd 15.5, and with the driving conditions on the coast of nc i have yet to be proven wrong. So to wrap this sillyness up the dod does not work as advertised, and if you want proof go on a test prive and watch the instant screen, on a truck with no miles it is even harder to get it to drop down to 4. Now if you are happy with the 5.3L dod, then my question to you is way are the AWD 6.2L 07 Escalades getting 17mpg after break in!!!

I took mine on a 6000 mile road trip. I got as bad as 16.5 average on the highway - huge headwind - and the best we averaged was 22.3. Driving conditions and the driver make all the difference. Now, I will say that the truck has 12000+ miles on it now and on our last tank that was all city, we averaged 17.3 but we were averaging 14.5-15.5 when we first got it with just under 6000 miles. I have witnesed and watched it go into 4 cylinder mode and stay in 4 cylinder mode while driving in the city. Granted, you barely have your foot on the pedal but it will accellerate and increase speed even in a slight incline. Of course once you give it some real gas, it pops back into 8. I have noticed that at speeds 30-45 mpg, it is better to get on it for the first 30-35 and easy up to the speed limit when conditions allow you to do so. Anyway, that is my 2 cents!!

Do you have a 4.10 or 3.73 rear end?

That is a real good question! I will have to look on the window sticker when we get it back from the dealer on Monday. I assume the 3.73 are stock?

quote:

ORIGINAL: MEVtopsail

Ok well i guess it is time for me to jump into this argument.....I am a salesmen at a dealership in NC, i bought a new 07 ltz and love the truck, and it is mostly all i sell. But i had a 02, and 05 both of them 4wd and i got 16.7 on the lie-o-meter, living at the same house, and driving the same roads and speeds to work.....I now have a fully broke in 07, and I get 15.3 on the meter. THE FUEL ECONOMY IS WORSE. All the literature the dealers get promise great things about dod/afm, but i will tell you now Mr. ZX1100F1, IT DOES NOT WORK AS IT IS MARKETED!!!!!!!!!!!!!! You can on average take 10% off the hwy mpg number and that will be most cars averages. NO ONE IS EVEN GETTIN THE ALLEDGED CITY MPG!!!! Granted people do not buy these for great gas milage, nor do i tell them they will get it...i tell them once you have broken in a 2wd you will average around 16.5, 4wd 15.5, and with the driving conditions on the coast of nc i have yet to be proven wrong. So to wrap this sillyness up the dod does not work as advertised, and if you want proof go on a test prive and watch the instant screen, on a truck with no miles it is even harder to get it to drop down to 4. Now if you are happy with the 5.3L dod, then my question to you is way are the AWD 6.2L 07 Escalades getting 17mpg after break in!!!

We've had no problem getting 19+ mpg hwy with 22 various GMT900 suv's in real world cross country tests.
One problem is that most people are coming out of several year old Tahoe's (very well broke-in) and going into 07 units and expecting a miracle right out of the gate, you have got to give this machine a chance.
A secondary reality is that now with gas averaging around $3 a gallon nationwide consumers are much more conscious about economy then they were when they purchased their last vehicle.

"16.7 mpg" is nothing to sneeze at from a vehicle this size (300lbs heavier than last year) that hauls 9 passengers and can tow a 7,700lb trailer, not all that many years ago I owned a K-5 that sat only five people, couldn't a tow tent trailer or get out of its own way and never got better than about 10mpg, for this matter a very good friend of mine drives a Toyota ext cab 4X4 Tacoma with a 4 cylinder and auto trans, would you care to guess what kind of fuel economy he gets on the highway?

FYI, these vehicles will continue to get improved mpg as the miles roll on, if yo don't have 30k miles on your Tahoe then it is not "fully broke-in".

It is for 4WD with the 4.10 as an option.

"For a descriptive and accurate account of what active fuel management is designed to do this is a good source of info: http://www.gm.com/company/gmability/adv_tech/100_news/afm_120605.html "



Too bad the marketing people at Chevy didn't read this when setting up the website info and sales brochure.

I've kept a spread sheet of my milage and like ZX said considering the size and ability of the Tahoe the milage is pretty decent in my humble opinion.
She is my daily driver, back and forth to work is 18miles one way I have the 3.42 with the 5.3 liter the ? marks are where I lost my piece of paper where I wrote them down...
The Avg Eco is per the DIC I bought her in October of 07 and didnt count the first 2 tanks as you can see I have never gotten less then 16 mpg and have had better then 20 mpg (but not listed at the time of fill up and reset)







Date
Trip Miles
Avg. Eco
Fuel used











4-Nov-07
440.3
19.2
22.9 

9-Nov-07
215.2
?
?

13-Nov-07
402.9
18.0
22.3

27-Nov-07
349.4
16.8
20.8

5-Dec-07
312.1
16.5
18.9

17-Dec-07
338.7
16.1
21.0

31-Dec-07
?
?
?

10-Jan-08
370.1
17.5
21.1

21-Jan-08
314.6
17.6
17.9

4-Feb-08
401.5
17.5
22.8

14-Feb-08
311.7
17.5
17.8

25-Feb-08
368.7
17.5
21.0

7-Mar-08
345.4
16.8
20.5

19-Mar-08
520.7
17.6
29.6

28-Mar-08
216
16.4
13.1

7-Apr-08
263.7
17.6
15.0

9-Apr-08
242.3
19.9
12.1

20-Apr-08
284.9
17.2
16.5
 
 

My two cents.  My previous daily driver was a 2001 Mustang GT with the 4.6V8.  It was rated 17 city, 24 highway.  Even when driven agressively I got 20.5-21 MPG which is exactly 1/2 way between the two ratings. 
 
So I buy the 2007 Tahoe and the window sticker says 16/21.  What is halfway?  18.5MPG.  So I'm expecting 18-18.5 if I drive the same routes and conditions as the Mustang. 
 
What do I actually get?  14.5 winter and 15.5 summer.  Even if I baby the Tahoe, I cannot get more than 15.8 or so on the same routes and conditions.
 
So.....I do not understand how two vehicles that went through the same Federal test routine could vary so much in actual MPG.  Unless things like APM really help in the test but not so much in the real world?  Which is why people are so negative about it.
 
I wasn't expecting to get 25MPG but this is the first and only vehicle I have ever owned which has can actually lay down a MPG average in every day drivingthat is LESS than it's CITY rating.  And my commute is about 60-70% highway.  If I'm in real city traffic I can get down to 12-13 pretty quick.
 
One of the people I work with has a Durango with the Hemi and MDS.  Not sure how she does it but she is averaging 16.5-17, sometimes even 18MPG driving in similar conditions.  The vehicles are of similar size and weigh about the same.  I don't know much about MDS but it seems to have an advantage over APM.  I wonder if the E85 compatibility holds back the 5.3?  The Hemi/MDS is not setup for E85.

I just read ZX's post about mileage on the vehicle.  I am at 42,000 miles and run M1 5W30 oil.  I did not see a noticeable MPG increase as my vehicle mileage increased.
 
Now when I owned a 2003, 2500HD CC with Duramax, the MPG's kept going up from 5K miles up until about 15K.  The DMAX engine did seem to require quite a bit of break in mileage.
 
We also currently own an 08 Impala with the 3.9V6 and the mileage on that hasn't changed much if any since day one.  That car is currently at 14K miles and averages 20.5.  When APM kicks in on the 3.9 your trip computer instant MPG's go from mid 20's to low 30's and APM will stay engaged up to about 70MPH on level ground.........

One of the Uber mileage techniques I have been doing is keeping the tach under 2k when accelerating from a stop Read up on some of the “hypermiling” http://www.hypermiling.com/
I think someone pointed out also that the vehicle has a lot to do with it. A Vette is sleek and arodynamic the Tahoe... well its a brick with rounded edges....

Actually the NBS Tahoe has a pretty low Cd.  Can't remember for sure but think it's around .38.  It's lower than any full size SUV including the Cayenne. 
 
Also based upon two years now, the DIC is .5-1.0 mpg high. 

Yes when I did my manual calculations based on milage and fuel to fill up it was about .5 difference it suprised me that it was as accurate as that.

The GMT900 Tahoe has a coefficient of drag of just .36
The Hybrid's Cd is .34
the Ford Focus is .32 and a Corvette .29 for comparison sake.

What makes up the .02 difference of the Tahoe's? Same body style right, I guess if you took of the roof rack you could reduce drag some and streamlining any protrusions underneath the body.  The real question is does waxing your vehicle make any difference...

The Hybrid also has slipperier front and rear clips and a drag redcuing rear hatch halo and side skirts.

Waxing your Tahoe does make a difference..............just not in fuel economy.

Here's my two cents...  I purchased the Tahoe over the Saquoa and Armada because of the advertised MPG.  I also have friends with both Saquoas and Armadas and all in all, I think I get the better MPG, which is great.  My only gripe about the AFM is that I think it could go into V4 mode more than it does.  I understand that when I start moving I want to be in V8 mode, but I also notice that as soon as I hit the gas the truck always jumps right into V8 mode.  So why couldn't they make it Idle in V4 mode and jump into V8 mode when you start moving?  Also, I've noticed often on down hills the truck will stay in V8 mode when it is just coasting down. 
 
Don't get me wrong, I think the AFM is great considering what it does, but I think they could have done a few things to squeeze out a little better MPG with the AFM. 

I understand GM not wanting to compromise any performace for the AFM  by not going into V4 or staying in V4 any longer then needed but sometimes I just need to adjust my foot or just barely nuge the throttle and it would be nice to keep that V4 for just a half second more.