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Chevy Silverado and GMC Sierra Active Fuel Management Problems



  • Did my trip this weekend. I averaged out to 16.3. It got about 15.8 on the freeway doing 70 - 75 on cruise control (pretty flat road going down I70 in Missouri), and then increased when I hit 60 MPH roads. That actually surprised me as about 55 miles of road is quite hilly with lots of curves and it handled it very well. I also drove like I was trailering something allowing my speed to increase going down hills and slow down going up, this kept it in v4 mode a good portion of the time. I think if I would back it off to 60 on the highway I could get the advertised 17.

    I do feel that GM has misrepresented the milage some though, seeing that even on my best driving behavior I can't get the stickered milage in either the city or the highway.

    I'll be taking it in this week to get it looked at though. As others have stated in prior posts, it feels like the motor is tugging going up hills and the transmission seems to hunt for gears to often. I've got 1300 miles on it now. If it can't figure out when it should shift in 1300 miles, then something is wrong. I'll be interested to see if I get the "It could take up to 7,000 miles" line that someone else received.
  • tafidtafid Posts: 12
    Yes, I was told the sudden engine speed increase while coming to a stop was normal, but I (for one) did not believe it. I even tried going through BBB Autoline, no good.
    I will be going back to the dealer. This time I will explain the problem differently. While easing into a parking spot, using only the brake, the rpm increases. At that point the AFM should not be switching from 4 to 8 or 8 nor 4, I would not think. This is the reason given as to why the rpm increases while coming to a stop. But after stopping, raising my garage door, and rolling into the garage the rpm will increase.
    You are right, I must put more pressure on the dealer.

  • I have about 14K on my 08 Silverado 5.3L crew cab LTZ. At this point I would say the AFM has performed flawlessly. It is impossible to detect the cylinder shift. I drive in southern CT where there are some hills, and a 60/40 mix of highway to city. I easily average 16 in that scenario, and on a trip where I am running at highway speeds up to about 70 MPH I have gotten as high as 19.2, but about 18.5 is more common.

    I do notice that if I drive regularly above 70, the AFM does not kick in as much, and it seems to stay off if I am pushing 80...which is normally too fast for me.

    So far my truck has proven to be world-class in every way. If I could have waited another 9 months I would have ordered with the soon to be released 6 speed transmission.
  • where did you learn that chevy would offer a six speed asutomatic for the 5.3. just ordered a 1500 ltz 4 weeks ago with 5.3 because of fuel mileage but will back out if you can tell me if thats a fact or wishful thinking.
  • I read about it in one of the initial reviews for the 2007 Silverado in Motor Trend, as quoted below:

    "Current predictions have EPA estimates hovering around 16 mpg in the city/21 mpg on the highway with the 5.3-liter V-8. Expect that number to improve when the six-speed transmission replaces the four-speed (both column shifters with an improved hand-contoured grip) in the SUVs and pickups in the next model year."

    I have not see much supporting documentation since. I am attaching the link from which this was quoted, the link is: l

    I think GM has always intended to use the 6 speed when it becomes available, but the total volume of vehicles (GM builds) that can accommodate the 6 speed is greater than available units, hence the phase in.

    I doubt you could bank on a firm date for the 6-speed phase in. My truck with the 4-speed has plenty of power and holds its shift points well, even when I am towing. I was very skeptical about buying the truck with the 4-speed, however, this particular unit is one of GM's more robust units.

    I looked at the Tundra because it had a 6-speed transmission, but felt it was not as good a value, and the fit and finish was better on the Chevy.

    You will not be disappointed with your LTZ selection as configured, I remain completely impressed with mine at now 15K and counting. I just finished a road trip today, in 4 Auto, in snow, ice and rain, and got 18.2 MPG.
  • thanks for the info. 18.2 mpg sounds good to me , compared with 11 mpg in my dodge 1500. truck was built yesterday, should be here 7-10days i guess i'll stick with it.
  • Well, I have the 5.3 on my "new" chevy 1500 2wd extended cab that is supposed to have the AFM. Ive put 22,000 miles on it since memorial day and have yet to achieve anything better than 18-19 (19 on a good day) MPG. BTW, the sticker said 22 hiway.

    My question for those who know, is if you have the truck without the DIC buttons, how would you know if AFM is active or not? The book says there is a display regardless of whether you have the DIC buttons or not, but fails to mention how one would know.

    I drive many days from gas station to gas station only touching the brake pedal and ignition when I leave the first station, stopping at the next one. 60-65 mph, cruise on, all highway. I drove 948 miles this week and might have achieved 18 mpg if I rounded it up. I generally get about 400 - 420 miles per tank and my fill ups are between 22.5 - 24.5 gallons. My simple math tells me that if I were to get even 20mpg, I should go 440 miles on 22 gallons of gas.

    No, I dont see any indication that AFM even exists. The serial number says it has it, the sticker says it has it, but other than that, there is no indication that it exsists or if it does, that it functions. Ive even driven 2 tank fulls with the trailer button depressed only to find the same exact milage.

    I love the truck, dont get me wrong. It's not the most comfortable for 6 or 8 straight hours, but it's a truck. My question remains. How would one know when the engine goes to 4 cyl. My next question (assuming there is no way for joe truck owner to know) is how would the dealership test it? Can they hook a computer up to it and see it function, can they engage the EFI manually or however AFM works? How can they show me that it is doing what it says it is or for that matter, even show me that it's installed?

    18 is ok? Thats 20% off the sticker. What if your wife was in the grocery store, bought $100 worth of groceries, and the store constantly failed to load more than 80% of those groceries in her trunk? What if you bought an air conditioner rated at 16 SEER only to find out it was a 13 SEER? What if the fuel stations only delivered 80% of the fuel the pump said it did?

    All I want to know is... Is it there, and if so, does it work (show me). It's a shame a coworker who has the same truck except his is 4wd and he gets over 20 per gallon with the same monthly miles and same type of driving.
  • stefkstefk Posts: 2
    is there a fuel pump in the single gas tank for a silverado 3500 duramax 6.6 ?

    also any suggested ideas on what to do when the truck doesnt start when it's cold or hot, mostly cold ?
  • fjthomasfjthomas Posts: 1
    This is my 5th truck which I ordered from the dealer in Maryland and picked up in January 08. After driving it about 200 miles I proceeded to drive to Ft Pierce, FL non stop. Generally speaking, I drove 5 to 7mph over the posted limit e.g. in a 55 zone I drove up to 62, in a 70 zone I drove up to 77.....almost always on 'cruse control' average for the trip was 18.4 mpg and the truck performed flawlessly. I now have 6000+ miles on the truck and it consistently 'averages' in the 16-17 area (mostly short 'around-town' runs).

    I find that the AFM is NOT noticeable by passengers but IS noticeable by me....though now I find I'v become oblivious to it!! This truck is a 5.3L, 4X4, LTZ with Stabilitrak. My last two trucks were a Dodge 2500 Diesel and a Chevrolet 2500HD Diesel respectively.......this '08 truck is far more economical than the Dodge and equal to the Duramax, though, I'm sure, it won't tow as much....its all a balancing act....the diesels are a $10K additive cost and the diesel fuel is 12 to 15% more expensive than regular......bottom line is that if you are not towing high weight trailers frequently it is far better to go with the gas truck!

    Prior to the Diesels I owned a Nissan and a Toyota.......wasn't happy with either of them!!
  • I have a 2008 chevy silverado with a 5.3 and active fuel management. I am wondering if there is a way to tell when the truck is running on 4 or 8 cylinders. Can you hook up a test light or something to that effect,
  • rjs1500rjs1500 Posts: 2
    I have heard that there is an issue with the Fuel management system when you put on a duel catbak exhaust. When it shifts to 4 cyl it makes a roaring sound? is this true and if so what luck has anyone had with finding one to put on an 08 silverado 1500?
  • rjs1500rjs1500 Posts: 2
    in your vehicle info on the dash it has an area to see the instant mpg and 4 or 8 cyl!
  • gmax6gmax6 Posts: 1
    Hey all you guys. I'm new to this site. But I'm not new to engines. For the average person this engine is a mystery. So is the AFM. First note that this engine is not your average beast. Far from it. This version of the Gen IV LS2 364 ci designated L76 in the truck is a de-tuned version of the previous years' Corvette base engine. The Corvette and Pontiac GTO LS2 versions produced 400 hp. This one is 367. The heads are high performance, high flow. The intake is from the 6.2L LS3. The valve train is a high lift all roller system. Etc. I could recite all the little technical details you hate to hear. But, what you really need to hear is... relax. What you feel when you are driving this truck is that engine loping because of the power. Not unusual for this type of engine. Plus you are feeling at stop the 4L70 automatic trans trying to pull that 10,200 lbs of load this truck was designed to do. This is one of the most heavy duty half ton pickups built today. The only manufacturer touting anything more is Toyota with 100 lbs more rating. Also lousy fuel mileage compared. I know a couple guys that have them.

    How can you see a difference in what you get as far as every day performance? I suggest you run the crap out of it occasionally. Also, if you are always running regular fuel, don't. Run a tank of premium or mid grade through her every so often. Or just add some to your regular. Right now no one offers a cold air package for them. K&N has a drop in replacement that helps. Few tuners out there too. Hypertech seems to be the best. Diablo just came out with theirs. Gibson has a great cat-back exhaust that helped mine. Sounds great without a lot of in-cab resonance. These alone have helped improve the mileage. But if you are like me you may not be able to keep your foot out of the throttle. I LOVE THIS TRUCK! If it didn't have a speed limiter (at 95) I bet it would pass 150.

    The AFM system only kicks in under the lowest load conditions. Down hill, tail winds, flat road. When on the highway try setting your cruise control just as soon as you feel it go into overdrive. Set with RPMs at 1500. Should be on 4 cyl. Look at your DIC. Should say somewhere around 24 mpg. Also around 45 mph. But most people can't stand to drive that slow. I can't. So I just drive the way I feel, within the law. HA!

    Anyway, don't treat that truck like a baby. It aint! You wondering when it'll break in? It wont until you use it. So use it.
  • You have afm,no dic installed,noway to tell if afm is working.For 17,000 miles I complained about really bad economy.Finally the lifters started tapping took it in for service the world class mechanic told me [they all do that piston skirt knock]I argued till he finally listened to the lifter tap.they replaced lifters plugs and wires.reprogrammed the computer,now I'm getting 20 to 24 mpg.But it has developed a mind of its own sudden accellation at stop rpm's raise from 500 to 1200 not all the time just every once in awhile.,\gm tech can't reproduce the problem,gave it back to me and said wait till it does it more often.Had a tick in the windshield,was told the bug deflector was the problem took it off still had the tick,they replaced trim inside the cab.Gas guage was saying less gas in tank,replaced a sending unit,fixed that,then a valve for the evap canister went out,fixed that.Of course I have called gm to,ask for compensation for the 17000 miles of 8-9 mpg they said no,I asked for the dic button to be installed,they said that is a dealer option,dealer said"As long as it does'nt cost more than a$100,they would cover it.Why would they say you have afm but no way to show it working,cuz they get $600. for it free,I have 87 chevy sitting in the garage it does a 11 second 1/4,at 112mph in four wheel drive,I've built a bunch of bowtiesbut this 2007 silverado has yet to impress me,nor has gm at this point.
  • mattbarry6mattbarry6 Posts: 1
    Okay, so this may be heresy but active fuel management is the new hype for most cars and trucks. I was looking at buying a new GM, preferably the hybrid Silverado when it hits the market but quite frankly I can't afford a LTZ model (which all hybrids come in) and I can't seem to sell my 1998 Jeep Cherokee 4.0L. So an idea hit me: why not put active fuel management on it.

    The proposed plan is to hook up a simple 5V programmable computer chip to 6 relays that shut off selected fuel injectors at 5 minute intervals (Just like Chevy does on its 8 cylinders). This is to operate the front three cylinders then the rear three cylinders intermittently. Its about a $75 dollar system once the relays, wire and board are purchased and about a 4 hour installation (3 hours of which is required for programming the C++ style board), but the hope is to see if active fuel management really makes a worthwhile difference in highway travel.

    Right now I achieve about 22 mpg highway (10 city) and have hopes that the old beast can get a few miles more per tank. Will keep you updated on whether or not active fuel management makes a difference on highway travel or if its something we pay more for from factory but get nothing for in return. Personally, a Prius doesn't sound too bad... if you like 76 horsepower and the ability to tow nothing.
  • branhapbranhap Posts: 10
    A few people with custom tuners or a custom tune have disabled AFM. Most people though with an active tune interested in improving MG make it more aggressive. Stock, AFM kicks on when throttle is less then 6%. A lot of people have bumped it up to 10% of throttle and had a noticeable change.

    AFM always turns off the same valves though. It doesn't alternate. It also turns itself off after 5 minutes of continuous use to prevent the active cylinders from overheating to much.

    In any case, this is my reading forums only. My 5.3L AFM is bone stock.
  • Is there anyone with the programmer in central Ohio? thanks Troy.
  • branhapbranhap Posts: 10
    I dunno. I've lived in Wyoming the past few years. Haven't lived in Ohio since 2001.

    As for tunes, the most popular one I read about is black bear tune. He basically sends you some equipment to plug into your truck, then you send him back the info tell him what ya want and voila. seems to have the most info on tuners.

    Good luck!

  • puttercaputterca Posts: 4
    you can add the DIC buttons yourself for under $60 and about 5 minutes of your time. all you need to do is order the switches and the replacement dash panel that accomodates the DIC controls. the harness to plug the switches in is already installed and just sitting behind your current dash waiting for you to plug into.
    I had the same frustrations as you and learned that this could be done very easily.
  • puttercaputterca Posts: 4
    don't expect the 6 sped tranny to drastically improve fuel mileage. from my understanding, the design is more to smooth out the shifting through the gears, not necessarily to add a high end gear.
  • bprepdahbprepdah Posts: 1
    Can anyone tell me where the EVAP canister is located on an '06 Silverado Crew Cab?
  • Really good post Gmax. After much debate, I just purchased a 2008 1500 Vmax. I was originally planning on buying a diesel, either a Dodge or Chevy, but after thinking about it I backed out of a diesel altogether. I just couldn't make the initial cost ($6500 extra) plus the premium on fuel work out on paper. I can buy ALOT of gas for that amount. Sure, I've heard alot of people tell me that a diesel will work alot longer, but I don't plan on keeping it for 500,000 miles anyway. Anyway, I've put about 700 miles on it so far and am very happy with it. I've read several complaints about fuel mileage, excessive shifting, stutter when going in & out of AFM, and rough idle. First, my mileage sets at around 18 mpg on average which I think is great for a truck that has the capabilities that this one does. If you want fuel mileage, buy a 4 cylinder. There's always trade-offs when it comes to power/ mileage. I thing GM has done a good job at coaxing 18 or so out of it. I was really expecting closer to 13-14. I do have the excessive up/ down shifting when climbing a pretty good hill but I've noticed that the reason that it does that is, when it downshifts, it has enough torque to quickly get it back up to speed, causing it to shift back up. I would suggest if that is a problem, drop the shifter down to 3rd to eliminate the "problem". As far as noticing it going in and out of AFM, it's very slight. The only reason I notice it is because it's a new feeling that I'm not accustomed to yet. The idle is defininately a little rough, but I think it's cool. All ponied up engines have a rough idle that I've been behind. All in all, I think it's a great truck and I can't wait to hook on to my trailer and see what it'll do. Anyway, just wanted to ad to your post.
  • jboehmjboehm Posts: 44
    I have driven a couple of different Silverado/Sierras with the Acitve Fuel Management. One thing I have noticed is that, when sitting at a stop light, the AFM will switch from 4-cyl to 8-cyl. Can someone explain why? (I know that I have seen documentation that that is the way it is suppose to work but I cannot locate a reason why).
  • tafidtafid Posts: 12
    I have the same problem. I notice that the rpm increases as well. If I stop, open the garage door, ease off the brake, occasionally the truck will surge up to 900-1000 rpm. Chevy tech service says it is normal, but did not explain why.
    How can it be normal to have your foot on the brake and the vehicle rpm increase and vehicle surge forward?
  • obyoneobyone Posts: 8,054
    Chinese multilevel marketing? Give me a break. Spam by any other name is still SPAM!!
  • astroman2astroman2 Posts: 1
    I have a new 2008 Sierra with 5.3l engine and about 2,000 miles. Once every week or two, when starting the engine, it sounds like none of the lifters have oil in them. The engine sounds like an old model V8 with mechanical valve lifters that are way out of adjustment.

    The valve clatter will continue but goes away by shutting off the engine and Immediately starting it again. The oil pressure is good and the dip stick shows oil is full.

    The noise only happens when the engine is cold or warm. Is AFM in control of the lifters and valves at startup?

    Has anyone had this problem?

  • natesmsnatesms Posts: 20
    I have the 6.0 in my Silverado and I have noticed that to, but very breifly on start up. It sounds exactly like you describe but goes away in a couple of seconds. I don't have to shut it off and back on.

    Let us know if you find out anything.
  • obyoneobyone Posts: 8,054
    The dealer will tell you that this is normal and happens more often with the 6.0 for some reason. For myself, it would disturb me. But what can you do?
  • I have the 1500 5.3 with AFM and have noticed an inconsistent vibration at about 55mph. There's a flat smooth stretch of highway I often take going home for about 7 miles and the vibration often occurs there between 50 and 55mph. It feels like I'm going over a course road surface but I'm not. AFM is sometime on and sometimes not. This vibration always occurs when I maintain this 55mph +/- speed for a time. It never happens in town and I have never noticed it at 65+. I've never ntoiced it at idle. Other than that I like the truck a lot. I'm a boring old fart of a driver but I get very good mileage. The lowest fillup I did gave 16.6 and highest has been 22.4. That 22.4 was almost all highway driving. Considering the power and size of this truck I think that's superb.
  • obyoneobyone Posts: 8,054
    50-55 mph is where most of the resonances in a vehicle converge for some reason. That's why there's no vibration at 45 or 65 but keep it at 55 mph and you've got a bumpy ride. This is usually attributed to the tires.
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