funky_junk

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.

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 dip**** parking your Vette didn't turn your $400 Goodyear Gatorbacks into rubber pellets.

funky_junk

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.

ZX1100F1

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.

73shark

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.

jmaynard

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!

ZX1100F1

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/...fm_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.

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!!!

TexasTahoe

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!!

73shark

Do you have a 4.10 or 3.73 rear end?