Active Fuel Management Useless.!

[ybsane]

I took the Suburban on its first decent trip over the holiday's traveling from Charlotte NC, to Wilmington NC. For all of yall who are local to the area know that hwy 74 is pretty flat and easy from Scotland County all the way across 95 to the bridge into Wilmington. Well I decided to take it easy through this area driving 65mph where you can easily go 70-75mph. I looked down at the real time monitoring were it shows the engine going from V-8 to V-4 and and your current MPG.

 

This thing kicked in and out of V-8 to V-4 more times than I can count, now I know a 4x4 Suburban has some weight to it but this was flat ground with cruise control set just to see how it would do. To me it is a waste I would rather have it just stay running as a V-8, mileage for the trip was good at 18mpg.But was is the purpsose of the AFM..?

[txab]

To raise MPG.

 

Many have had AFM turned off on their vehicles with little or no change in mileage

[pinky93]

To raise MPG.

 

Many have had AFM turned off on their vehicles with little or no change in mileage

 

 

I have just ordered a Diablosport Predator tuner, with the main reason being to turn that crap off.....I have installed a Magnaflow exhaust and the sound drives me crazy when it goes to V4. I have also installed a Volant cold air kit and some E3 spark plugs, so I am interested if my mileage gets better....

[compulynx]

There is a point where AFM becomes non-usefull. Those 75 mph highway speeds will not make good use of it.

 

I did a test in my 08 Sierra traveling back and forth to my wife's parents in Ocala, and the magic point was 62 mph. On a flat road, 62 stayed in 4 cyl mode, anything above that started the in and out thing. The wind resistance just requires 8 cyl at anything above that speed. Since the Burb is a little different aerodynamically, your "magic" point may be higher or lower.

 

It was also a big difference in mileage. At 62 mph, I got 21 mpg. At 70 and above, 17 to 18 was all I got.

 

Personally, I just slow down and enjoy the view. Only made 20 mins difference in the trip time. I can deduct part of that 20 mins as less time at the gas pump.

 

C

[Jubei69]

There is a point where AFM becomes non-usefull. Those 75 mph highway speeds will not make good use of it.

 

I did a test in my 08 Sierra traveling back and forth to my wife's parents in Ocala, and the magic point was 62 mph. On a flat road, 62 stayed in 4 cyl mode, anything above that started the in and out thing. The wind resistance just requires 8 cyl at anything above that speed. Since the Burb is a little different aerodynamically, your "magic" point may be higher or lower.

 

It was also a big difference in mileage. At 62 mph, I got 21 mpg. At 70 and above, 17 to 18 was all I got.

 

Personally, I just slow down and enjoy the view. Only made 20 mins difference in the trip time. I can deduct part of that 20 mins as less time at the gas pump.

 

C

 

 

I agree, when I used to drive my gf's Toyota Camry I drive 70-75 mph using cruise control; but in the Siearra I keep my cruise at 60 mph. Driving 60 mph versus 75 mph makes all the difference in the world... I never hammer down, not even for passing, I gradually pass; every now and then though I hammer down on the 5.3L to get around a big rig or crazy driver.

[yettavr6]

I live in a very rural area with little traffic and typical speed limits of about 45mph (meaning I'm usually going 55-60). In my case the truck runs in V4 mode pretty frequently and shows anywhere from 24-32 MPG...granted I did JUST buy the truck and just started my first full tank today so I can't give any actual MPG average, but i think for the roads around here the AFM is very useful.

[brims]

I see 24-30 instant MPG on the dash a lot and I have AFM turned off. At slow, constant speeds on really flat ground, it may work. But in a truck, I don't see it being useful.

[VRSCA1]

I agree I have been experimenting with my AFM on my 09 sierra,I have come to the conclusion that once you are exceeding 65mph its useless,it should just disable itself why go in and out of v8 at speeds over 65 whats the use?

I speed most of time on the x-way and in the city my avg mileage is only 14.7mpg

I think its about the same as what got with 94 z71 4x4 1500 chevy ,I did cash for clunkers took the 4x4 sierra...maybe 1 MPG diff. total anyways thanks OBAMA!

[butzers09silverado]

I have an 09 ext cab z71 with 5.3 and 3.73, i have some terrain here in ct, and it is REALLY hard to keep in 4 mode, you can't use cruise because of hills, and I lose 10mph trying to keep it in 4... i haven't seen over 19mpg even on a road trip to buffalo doing 68...

 

I'm going to try 62 and see if that works, but i'm taking suggestions on speed with 5.3 4spd 3.73 gear. you can hear the difference, and feel the jerk when it goes into 8, but i wish i had full dic....

 

thanks.

[pm26]

But was is the purpose of the AFM..?

 

To have something else to break and annoy you.