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fuel management system?


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#1 remark

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Posted 06 October 2013 - 11:34 AM

how does that actually work? it goes into and out of 4 cylinder mode all the time. i thought it was suppose to go on when you're on the highway? mine goes back and forth from V4 to V8 even at a steady speed. whats up with that? no wonder the gas mileage sucks.

#2 MikeNH

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Posted 06 October 2013 - 12:52 PM

It will go in depending on load and the factory calibration for it is useless. If you're in town I suggest running the transmission in M4 or M5 so it will always be in V8 mode. I've since had my truck tuned and AFM totally disabled and haven't looked back.

#3 remark

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Posted 06 October 2013 - 01:48 PM

is your mileage any better? i would assume it would be in V4 all the way to work.all highway 28 miles, but i get 17 miles to the gallon. it should be like driving a honda to work, instead it's like driving a steam roller.how do you turn off the AFM?? will the dealer do it?

#4 Daryl Z71

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Posted 06 October 2013 - 01:55 PM

is your mileage any better? i would assume it would be in V4 all the way to work.all highway 28 miles, but i get 17 miles to the gallon. it should be like driving a honda to work, instead it's like driving a steam roller.how do you turn off the AFM?? will the dealer do it?


The Dealer will not turn it off. You'll have to get it tuned, or buy the Range unit that plugs into the OBD 2 port.

Edited by Daryl NHT, 06 October 2013 - 01:55 PM.

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2006 Silverado Z71 - 232,000 Miles and Counting...


#5 MikeNH

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Posted 06 October 2013 - 03:18 PM

is your mileage any better? i would assume it would be in V4 all the way to work.all highway 28 miles, but i get 17 miles to the gallon. it should be like driving a honda to work, instead it's like driving a steam roller.how do you turn off the AFM?? will the dealer do it?


I'm not sure about mileage because once I ran the tune I switched to E85 and also got slightly larger tires. Over the summer I made a trip back to NH from Michigan and was in the mid 17s where I used to be able to get mid 18s with that type of driving. But that loss is probably more tire related than anything else. I didn't disable the AFM to save gas, I hated how it felt with the exhaust I installed when it ran 4 cyl mode. Power is more important to me than fuel efficiency and since I couldn't swing an extra $3k for the 6.2 I've done what I could do maximize what the 5.3 can do without major mods.

#6 Blue Sierra Owner

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Posted 06 October 2013 - 07:01 PM

Yes the AFM system programing on the GMT-900 trucks is not very good to say the least. On my 09 all I had to do was think about the gas pedal and it would change back to V8. I get a tune from Black Bear and it helped tremendously. I turned off AFM, upped the speed limiter and turned down the torque management. The V4 mode is not going to save you very much gas at all I hardly saw any impact with my truck on MPG after the tune. On another note my 2014 seems to stay in V4 longer and gets a lot better MPG than the 09 did. I believe it has nothing to do with the AFM though as my 09 had the 4 speed and this one has the 6.



#7 pezboy

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Posted 07 October 2013 - 10:39 AM

It switches a lot less while cruise control is on. Even with cruise on it can be in V4 and then with a slight uphill grade it will switch back to V8. If you are going over 60 mph it won't switch on very much. I get pretty good mileage considering I have 4.10 gears and I think it is due to the AFM or the hilly terrain here.
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