Do You Like Chevy's Active Fuel Management System? AFM Problems?

Discussion in 'GM Powertrain' started by Restlessone, Feb 28, 2009.

  1. Restlessone

    Restlessone New Member

    I was wondering what the opinion of the group on GM active fuel management. Is this system reliable, it seems very complicated.? Could it be disconnected and the truck still run ie pulling a fuse or something.
    Obviously I don't understand the system so I look forward to your commrents
  2. TRPLXL2

    TRPLXL2 New Member

    I don't know a thing about the active management system either, but I do know it switches from 8 cylinders down to 4 cylinders. My personal opinion is the dealership can't even fix a traditional fuel injection system, so how the hell are they going to keep up with this stuff. I have heard the speech a hundred times from the ASE certified technicians, "They send us to school all the time to keep up with all of the upcoming technology." Well how can you move on to rocket science when you haven't even completed biology, the concept of it is awesome but how does it really perform. Thank you for asking this question, I am curious about some of the answers that will pop up............AMY
  3. Restlessone

    Restlessone New Member

    Yeah it seems you know about as much as I do. I was hoping with the fountain of knowledge on this site someone would jump in.
  4. Restlessone

    Restlessone New Member


    No response, I'm shocked.
    I'm really just trying to find out if this is a reliable system. When the warranty runs out will you have to replace expensive solenoids. There must be somebody out there with this system on there trucks.
  5. DrewsZ71

    DrewsZ71 New Member

    I have the AFM on my truck. Ive had it over a year now and it seems to work flawlessly. I havent had any problems with it. If you drive on flat roads and highways, it'll will save you some MPGs. I live in a hilly area so it only cuts down to 4cyl mode when im on flat spots or coming down hill. Theres been several times ive done 70-75 mph on the freeway in 4cyl mode getting 36mpg. The changing from 4cyl to V8 mode is seemless there is no harsh bumping or jarring whenver it changes. I like mine, I could still live without it buts its just a lil bonus for me i
  6. Dickie

    Dickie New Member

    I have it on my truck havent had any problems with it yet knock on wood....Mine dont kick down to often with the way I drive
  7. Restlessone

    Restlessone New Member

    One more

    Thanks for the replies. One more question, can you adjust the system or turn it on/off.

  8. chance

    chance New Member

    Why would you want to turn it off, Its designed to save you money?!? The system is actually more simple then you are thinking and Im pretty sure it is mostly controled by the engines computer simply turning off the injecters and cuting the ignition to the 4 cylinders (no expensive solinoids). I also believe that throttle position, and vehicle speed determine whether the AFM is operating or not.

    just my .02 cents
    Last edited: Mar 1, 2009
  9. ChevyFan

    ChevyFan Administrator Staff Member

    You can easily turn the system on and off, with your foot on the accellerator. :lol:

    I've driven multiple different Silverados with the AFM in them and it's very impressive to watch it work.

    The system is only moderately complicated and GM tried to do it in the early 80's but the computer technology wasn't advanced enough to handle it. The engine has been redesigned to allow for exhaust valve to stay closed when the computer determinds that there is a low demand on the engine. That essentially keep pressure inside the value and then the next rotation the intake valve is kept from opening as well. The gas pressure inside acts like a gas spring essentially.

    All this sounds like it's complex, but it's really just 1) shutting off the fuel, 2) shutting down the exhaust value, 3) shutting down the intake valve. Then when power is needed, the exhaust value opens up, followed by the regular cycle of the engine. I think they started upgrading the engine with some type of solinoid system now to make this all work and only like half of the cylanders can be deactivated at any one time.
  10. chance

    chance New Member

    i did a quick search, i found this on wikipedia. i know its not an officail site but it supports what was previously stated by steve and corrects what i had thought.

    In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.
  11. Restlessone

    Restlessone New Member

    I'm old and the increasing complexity of these vehicles make me nervous. What happens in 10 years, is this system still going to function or cost a lot of money to replace. If it can be turned off then you can just ignore it. I keep my vehicle for a long time and expect this will be my last so I am agonizing over what I should buy.
    I sound like my father but I really long for the simplicity and reliability of cars and trucks from my youth.
  12. ChevyFan

    ChevyFan Administrator Staff Member

    Vehicles built today are much better then there were even 5 years ago. I think that's one of the problems of the auto makers, they're building cars and trucks that you don't have to turn in at the end of 4 years .... in the 50's that's the life of a vehicle, today that's just getting broken in. The fuel savings has been estimated to be as high as 10% in some estimates. That's portentially going to save you maybe 500 gallons of fuel over 100,000 miles at $2.00 per gallon you'll save $1,000 over what you would have spent. If you had that technology during the $4.00+ gas peak you could double that figure in savings costs.

    This stuff doesn't scare me, as much as the entire engine is computer controlled anyhow, and the transmission and the ABS and traction control and everything else.
  13. morest39

    morest39 New Member

    Does A/C being on affect AFM?

    A friend of mine said that a mechanic told him, that if you run the A/C the engine will never go to 4 cyclinders. He says he's confirmed it with his DIC fuel mileage computer. How do you know when it's on or off?
  14. Restlessone

    Restlessone New Member


    Well I bought a Silverado with the active fuel management and am very impressed (so Far). The change from 8 cyl to 4 cyl is not at all noticable. If you put your DIC on instantaneous fuel reading it tells you hom many cylinders are working, and yes it still goes into 4 cyl mode with the AC on.
  15. vncj96

    vncj96 New Member

    My dad has the 6.0 in his with AFM for his 07 NBS crew Z71 and he easily gets combined MPG of 18-19 and on long trips up north with the truck bed loaded with camping stuff and coolers of beverages and four people in the truck he can get 23-24 MPG even at 70MPH this is all falt and on the highway, but this is a very capable system and it has worked flawlessly for him for two years now in his truck
  16. oliverman

    oliverman New Member

    I am new to this website and I also have a problem with afm, that is why I registered. I bought a Certified 2011 avalanche with just under 12,000 miles on it. When I am going 55 mph and keeping the speed even, it runs on 4 cylinders and starts vibrating through the steering wheel, seat, and gas pedal. Also when I do a right turn no stop, the truck acutally jerks when stepping on the gas to start speeding up. I have had it into the dealer about 5 times in the last couple of weeks and they feel the vibration and say its normal and they will not admit anything is wrong. I
    e-mailed GM and it seemed like they were going to do something, but today they called me and said nothing is wrong with it, that all afm engines vibrate. I know several people with this engine and they all say they shift flawlessly. I know they make scanners to shut it off, but my dealership and GM both said I should not disconnect it because it will void warranty. I traded in a Yukon and they have already sold it, so I am between a rock and a hard place. I wanted an Avalanche before they were gone, and its a great vehicle except for the vibration and jerking, but may have made a big mistake. Has anyone been able to shut off afm?
  17. aloxdaddy99

    aloxdaddy99 New Member

    I have it shut off in my truck. I noticed a lag when slowing to make a turn and than excelerating. Because of the lag the truck did "jump" a little. That is a major reason I purchased a Diablo inTune. it also help with the power and mpg's.
  18. jswain

    jswain New Member

    I have an 08 GMC with afm. It gets 1 mpg better than my 94 Chevy did with the 350. Both Z71, 3.73, 4 speed auto. The 08 has 54k miles. The 94 had 212k. It will no doubt make engine work more expensive when the time comes, and from researching the net, it looks like afm causes some reliability problems. Google "afm lifter" or "afm oil consumption". Kinda scary. The only way of turning it off is a tuner. I don't trust it, but it seems to be the future. I once heard the quote "complexity is the enemy of reliability". Some truth to that, I imagine. The hemi has it also. And then there's the two turbos on the ecoboost. I'm not so sure the added technology is worth the added price tag, all in an effort to save fuel. Not sure how long you'd have to drive one to get that money back. And I have no doubt the added technology will cause some issues. Is a six speed auto more complex than a 4 speed? Yup. Are there more moving parts to fail? Yessir. Will it cost more to rebuild? Sure. I figure its the same way with an afm versus non afm engine. Now if I was getting 20 mpg, I'd say it was worth it. 16 mpg, not so much.

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