I disabled AFM as an experiment.

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by stchman, Aug 26, 2013.

  1. Cowpie

    Cowpie Rockstar 3 Years 500 Posts

    Yeah, the DIC fuel mileage is more vehicles is off somewhat. We have that issue especially regarding heavy semi trucks where tracking mpg is very important for cost benefit analysis. On my semi, I installed a ScanGauge D and then calibrated the output to match real world mpg figures, and now I can get true instantaneous and average mpg numbers from the display in real time. By the way they have the same device available for everyone's car and pickup also, and it can provide extra information from the ECM that there is no dash gauge for. And you can clear fault codes with it!

  2. Sierraowner5.3

    Sierraowner5.3 Epic Member 5+ Years 1000 Posts

    i know my DIC tents to read a touch high, ive checked it against pen and paper about 6 times, it tends to read about .3 mpg high, and its consistent about it.

    i can live with that.

  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Mine reads high on mpg while driving and overall avg is roughly 2mpg low, Ive been keeping a record since day 1.
    The fuel used counter is almost spot on since the first day.
    I started doing paper/pen calculations after watching the DIC in the wifes HHR and realizing at times it was wildly optimistic.
  4. stchman

    stchman Active Member 2 Years 1000 Posts

    From the DIC, but the DIC on my trucks reads within ~0.5MPG either way.

    The switch from V8 to V4 to V8 is virtually instantaneous. AFM does not make the truck "feel" different. Since I've had the AFM off, the truck feels the same.

    There is no lag from switching between V4 and V8. Any perception otherwise is pure conjecture.

    So far the AFM is proving to have no benefit to real world fuel economy, and there does appear to be a more than fringe number of people having oil consumption issues. As long as I get the same fuel economy, the AFM can remain off.
  5. Sierraowner5.3

    Sierraowner5.3 Epic Member 5+ Years 1000 Posts

    what people are calling the lag is when you stand on it and go to pass someone, the truck switches to V8, then down shifts, it takes it a second, and that is very noticeable.

  6. stchman

    stchman Active Member 2 Years 1000 Posts

    IMO it's all in people's minds. I've been driving AFM Silverados since 2008 and have never noticed a lag in throttle response. The switch from V4 to V8 is virtually instantaneous.

    The delay for the transmission to downshift is not from AFM, but from GM wanting to keep the truck's RPMs as low as possible for as long as possible.
  7. ChevyFan

    ChevyFan The Sheriff Staff Member 5+ Years 1000 Posts

    Early on with the afm, even gm admits that there was a hesitation when moving back from v4 to v8 mode. I think they've said that was only on the first year or two.
  8. ChevyBoy2009

    ChevyBoy2009 Rockstar 4 Years 500 Posts

    Have you ever pulled a trailer?...more than a golf cart or a lawn mower?...you will feel the diff when it switched when your pulling a 5k trailer going up a hill or passing someone...dont tell me its the tranny its NOT...while watching the DIC and feeling it,you will know...and it does make it feel different going down the road with it off!...the sound off the exhaust being "normal" makes it feel diff also...pull a trailer and you will tell the diff...
  9. stchman

    stchman Active Member 2 Years 1000 Posts

    I have pulled trailers and hauled heavy loads. The lag you are feeling when trying to pass someone while pulling a 5K lb trailer, IS the 5K lb trailer. Also if you are pulling a trailer as heavy as 5K lbs, it is highly advisable you switch to tow/haul mode.

    If you are pulling a 5K lb trailer UP a hill, the engine will NEVER be in V4 mode.
  10. ChevyBoy2009

    ChevyBoy2009 Rockstar 4 Years 500 Posts

    Bad example chief...forget that last post...yes i know part of it is the 5k trailer...and i DO use tow/haul mode getting up to the speed i need to be...then i turn it off...im not gonna argue here...you must have that "special" one...read this

    From www.edmunds.com...

    Since this is a site dedicated to car purchases, I'm certain Edmunds would want their readers to know what other new owners are saying:

    If you're considering a new 2013 GMC Sierra or 2013 Chevrolet Silverado make sure you take it on a long test drive at 45 mph on level ground. Turn the Driver Display to Instant Economy. Ask the salesman if the Active Fuel Management AFM is seamless from four cylinders to eight. Sure GM says its seamless from eight to four. You're essentially coasting. During the test drive, determine if the transmission is growling as the AFM activates all eight cylinders. Make sure you grill the salesman with questions such as "has General Motors received overwhelming complaints about this transmission"? "Have they received complaints about clunking"? "Are there General Motors maintenance directives referencing all of the complaints"? "Do the directives instruct the dealer to avoid the issue and tell the owner "it's operating as designed"?


    In their latest seasonal publication, GMC The Magazine, on page 5, they state the "engines seamlessly switch to four cylinders." Hey GMC Magazine, why not describe the opposite, the switch back up to eight cylinders? Oh, that's right, I'm sure omission of that little tidbit was an oversight! The switch up to eight IS FAR FROM SEAMLESS. It's actually incredibly annoying and no, you never get used to it. A friend put dual pipes and glass packs on his. That makes the growling and lagging even more noticeable.

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