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Chevy Silverado and GMC Sierra Active Fuel Management Problems

cadillac5cadillac5 Member Posts: 1
edited June 2015 in Chevrolet
There is a problem with the active fuel management systems on ALL 2007-2008 Sierras that have the 5.3L or 6.0. The 4.8L model does not have active fuel management. For the old timers out there, it is the same issue as the Cadillac V8-6-4 engine. Make no mistake, If your vehicle has active fuel management, you have a problem! GM is aware and do not have a fix for this issue.

See Also: GM's Active Fuel Management and Oil Consumption Issue


  • 1offroader1offroader Member Posts: 208
    What is the problem, exactly? You need to be a little more specific. I have 11,000 miles on my 6.0L Silverado and the only problem so far has been excellent fuel mileage and seamless operation.

    It IS NOT the same system as the old 8-6-4 Cadillac. They are COMPLETELY DIFFERENT in design and operation.

    Get your facts straight, then post when you have something more to say.

  • anythingbuttoyanythingbuttoy Member Posts: 102
    I have a problem? Thanks!!! I'll rush right down to my dealer right away and tell them: "Hey, I have a problem with my AFM", he'll say: "What's the problem"? I'll say: "I have no idea, but some dude on Edmunds.com said everyone with AFM has a problem with their AFM".

    Whew, glad I found this thread, cuz till now, my 6.0 has been running flawlessly.
  • lionclawzlionclawz Member Posts: 12
    My 07 Has NO PROBLEMS. Which comes back to the accuser to provide viable proof instead of mindless jargon.

    I cant help but think back to the writing style which is similar to one I haven't seen till now.

    Time to get back to reading issues that are reality based from Chevy owners.
  • obyoneobyone Member Posts: 7,841
    Attributing intent to trolls is a very difficult issue since by its very nature to call someone a troll is to already assume an intent, that they are posting only to cause problems. So once a person is called a troll they have already been categorized by the speaker as someone with a certain intention.
  • teamimpactteamimpact Member Posts: 2
    My 2007 Vortec Max has only one problem It Runs Great and my wife thinks I love my truck more than her :)
  • asylum575asylum575 Member Posts: 72
    What kind of fuel economy do you get with a 6.0 with active fuel management
  • 12ozcurls12ozcurls Member Posts: 65
    yeah i second that..whats everyone gettin in terms of milage..
  • santaman58santaman58 Member Posts: 3
    Hey I'll stand right there with you and agree with there being a problem. My 2007 New Body Silverado 6.0 liter with max trailering has been running like crap since day one. Thought it would break in and the issues would go away...not! Its been to dealer and they told me it needs more time to have the fuel cells trimmed because it is a "smart" truck...I HAVE 3000 MILES NOW and it still runs like crap. It stutters and tugs going up hills and doesnt know when to shift. Plus it has a distinctive rough idle. It has a subtle noticeable pop when AFM kicks in and it sucks to drive it. It is going back to dealer again soon but they are saying that it might take 5000-7000 miles before the brain learns my driving habits. HEY!!!!!!!!!!!!!!! I shoudlnt have to wait for that long to have a truck run correctly! THERE ARE PROBLEMS OUT THERE WITH THESE TRUCKS CAUSE I HAVE ONE ONE OF THEM! If I drive in third gear and AFM doesnt kick in then the problem is gone...rough idle still exist though....so I say that the AFM is the culprit. GM needs to address this issue and notify dealers how to correct it. I will continue to take mine back til its fixed or lemon lawed! When you spend this kind of money you should receive a solid good running vehicle! 2 dealers are now telling me that there is nothing they can do! BULLCRAP! I have owned many chevys and this is the worst running one I have ever had! For those of you who are lucky to have a good running one, realize there are many of us out there that have bad ones! as the forums will show! :mad:
  • akflyerakflyer Member Posts: 1
    Just purchased 2008 Z71 Siverado 1500 5.3L 3300 miles both sensor causing engine hot error and fuel sensor back ordered, problem seems to be wide spead and cold related accordin to local dealer in Anchorage :(
  • tafidtafid Member Posts: 12
    I agree that something is not right. This my experience.
    When easing to a stop or after stopping and slowly rolling (by easing off brake, no throttle apply) into my garage, the engine speed will increase surging the vehicle forward. It does not matter if the engine is cold or warm, nor driving for one minute or one hour. The engine speed will increase up to ~1000 rpm or more. The engine speed will surge and slowly come down to ~600 rpm in less than 15 seconds. This problem does not occur all the time, but I can bet on it happening each time I drive.
    This condition is known and called normal (by GM) with Silverados with AFM. I tried to get someone at Chevy to see that a vehicle accelerating on its own is not right. No luck. They don't talk to you, they send customer service to deal with you instead.
    So I will need to live with the condition and hope the sudden accel does not get someone hurt.
  • 1offroader1offroader Member Posts: 208
    I have AFM on my 2007 Silv. w/6.0. It doesn't do anything like you describe. In fact, AFM 4 cyl. mode does not even engage at speeds less than about 15 mph. I think it is WAY premature to blame your problem on the AFM system. It could be a malfunctioning engine control module, a sticky throttle body, etc. There are many things it could be besides the AFM. I am in no way downplaying your problem, just pointing out it very well may be unrelated to AFM. Good luck solving the problem, please post when you do. So far at 13K no problems, I like my Silverado. It's not perfect, but what is? It's the best 1/2 ton truck out there now, for a while anyway, at least until the Ford and Dodge re-design in a couple years.

  • tafidtafid Member Posts: 12
    Thanks for the comment. I am not the one who said my sudden accel issues was caused by the active fuel management system. The company (Chevy) told me that the reaction I am getting is normal with all Silverados with AFM. I agree that there seems to be another issue, but no one will listen or acknowledge it. As I was verbally told in the beginning of my attempt to get his resolved, there is no calibration for this issue 'at this time'. So I am stuck with a vehicle not functioning properly. There are no safety concerns and therefore no urgency on their part.

  • 1offroader1offroader Member Posts: 208
    I don't care what the Chevy dealer is telling you, it isn't true. I don't experience any of those symptoms. Nor do most other Silverado owners. The dealer may just be trying to get out of fixing it. Don't allow that to happen, stand your ground and get it fixed.

    A vehicle surging forward unexpectedly, such as you described in your earlier post, is most certainly a safety issue and you should present it as such.

  • natesmsnatesms Member Posts: 20
    I recently bought a 2008 Max with the 6.0 and I have the same concerns that you posted here. I have a rough idle (it seams low to me to, 450 - 500 rpm when in gear and stopped). The RPM's bounce around a little when you are sitting at a stop light.

    I also have the same tugging issue when you go up hills. That one really bugs me, you have to give it some gas to get it to downshit to make it stop. There is also no question when AFM is kicking from 4 to 8. You feel it, even at highway speeds.

    I just got this vehicle so I'm hoping the computer learns over time, but I'm not convinced. I test drove a 5.3 version for 3 days and loved it. Didn't have any of these issues at all. Everything was smooth as could be. When my 6.0 got to the dealer, I hoped in, ran around up the highway and back and bought it because of my fantastic experience with the 5.3. Now that I have it at home I'm really starting to get concerned. Does anyone else have some insight on their experiences? I'm not jumping to conclusions yet as it only has 200 miles on it, but these things have jumped out at me compared to the 120 miles I put on that 5.3.

    Also, fuel mileage. Anyone able to get anything close to the sticker on the window? I ran 35 miles on flat road at about 60 - 70 mph and averaged 13.4...holy crap!
  • tafidtafid Member Posts: 12
    Thanks for the support.
    I even tried going through BBB Autoline to get help. Thought they could help mediate. But the BBB Autoline is funded via the auto industry. They say they are impartial, but.... I am trying other approaches, like this forum. Someone knows there is an issue, or that this is not NORMAL.
    BBB Autoline makes you prove there is a problem. So it is you against the auto company.
    I am a customer who is not satisfied, though GM says customer satisfaction is important to them. I'm sure.

  • 1offroader1offroader Member Posts: 208
    Your mileage is horrible, there is something wrong. Doing 70 mph on flat fwy. I expect 18 mpg. I have gotten as high as 18.5. No foolin, done it many times. Of course thats assuming you are not hitting the throttle hard getting on the fwy. etc. Even so, in bumper to bumper commuting traffic I get 15. The weird surging and the bad mpg may be related. Don't accept what the dealer is saying.

    As to idle, mine fluctuates a little but that doesn't bother me, it's a truck not a Benz. As long as it doesn't make me spill my beer it's not excessive. :surprise:

  • natesmsnatesms Member Posts: 20

    Thanks for the comments. I went out this weekend and put another 250 miles on it to bring my total up to 500. I did another 15 mile run at 65 - 70 mph and my mileage was up to 15.5. I think I'll give it another 500 miles and see where I am at, it might really just need to break in some more.

    The idle doesn't bother me, I just noticed it because my old F150 never so much as shuddered. If it was shuttering it meant yet another coil pack went out (stupid, stupid design, first thing I did with this truck is pop the hood and make sure something similar didn't exist. Looking forward to being able to park this truck in a rain storm without fear).

    I must say I do not like the AFM very much though. It is noticeable when it turns on and off. After some more research this seems to be normal and a common complaint among owners. From other things I have read it seems to be more prominent with the 6.0 than the 5.3. On one website, out of 6 reviews it was listed 6 times under the cons section, but often with a note that you get used to it. The thing that is weird to me is that I get a "surge" (acceleration) when it goes into v4 mode, the switch back into V8 mode is smoother. I would think it would be the other way around.

    I'll post my mileage again once I hit 1000 miles, and any other developments along the way. It'll probably be 2-3 weeks unless I decide to take a road trip next weekend.

  • natesmsnatesms Member Posts: 20

    In my limited experience with this truck I have yet to experience anything like what you are describing. I agree with 1offroader about sticking with this until you get it resolved. I'm amazed that they don't see it as a safety issue. Have your buddy call them after he gets pancaked between the bumper and a trailer as he is guiding you back...

    Keep us posted.

  • canwcanw Member Posts: 3
    Santaman: Yep, I've got an '08 Silverado VortecMax 6L that I bought in Aug. 07 with the same issue. Dealer says everything runs up to the computer spec so it is "just the nature of the beast." When I got nowhere with the dealer, I went to GM and their tech people say the same thing; "the rough idle I experience is normal for that vehicle." Like you, I didn't notice this issue until about 200 miles on the odometer and my name was already on the bank loan. Too bad for me I guess. And yes, the AFM delivers about 13.5 mpg on my truck too. I'm sure that doesn't help GM's fleet average.
  • 1offroader1offroader Member Posts: 208
    I do not understand where all the lousy mpg is coming from. I get an honest 18 on the fwy. at 70 mph, in cruise control. Maybe that is the key, having it on cruise control.

    As to the afm, I have had a friend try to tell me when he thinks it goes from v8 to v4 while riding in the passenger seat, he can't do it. I can tell, just barely, if I am driving because I have a foot on the throttle and it is just barely noticeable if I am concentrating on it. Otherwise not.

    Genuinely sorry for your problems, but do not let the dealer tell you that surging is not a safety issue, it most assuredly is a safety issue. Get it fixed before someone gets hurt.

  • ponch1ponch1 Member Posts: 1
    Hey everyone! Im new to this post, and let me share my experince with my 2008 VortecMax with everybody...I bought this truck 4 month's ago, and like some people on here I thought that this "rough shaky" idle I am experiencing would go away after a few hundres miles, I too thought it was the computer going through a "learning mode". After 1000 miles I took my truck back to the dealer, and had them try and diagnose this problem. They ended up doing a computer upgrade (crankshaft position sensor relearn). I got my truck back and it ran absolutely the same as before, I would have turned right around and gave it back to them, but I needed my truck that day, and didnt have time. I took it back a few days later, and told them to not call me until this problem was fixed correctly.... so I get a call from the dealer, and they inform me that they called general motors, and that GM is saying "this is a normal characteristic of this engine". I was dissatisfied, so I looked in my owners manual for the 1-800 number to GM customer service, and wanted some answers as to why this is normal. Let me tell you people that this was a COMPLETE waste of time for me. They wont get on technical terms with you, or connect you with someone from an engineering dept, instead they give you a mailing address to write to in detroit. I went that route, and sent a letter to them 2 MONTH'S AGO, and never received a call from them. The only thing they did for me was send out an area rep from GM to look at my truck's problem at the dealership. This clown cared more about getting home because he was tired, and told me more about his personal life etc...bla..bla., and didn't care one bit that I was dissatissfied. They tried to keep me happy by extending my warranty for free, but that does NOT fix the problem. I then wanted my money back, and was gonna hand them the keys, but I was told that I cant do that, and that I have to go through a long drown out process of contacting a lemon lawyer, and other things. I also learned that you should NEVER sign an arbitration agreement, when buying a vehicle, (which I signed accidently). All in all, I am DONE with general motors...mainly because of their terrible customer service,...I will continue to tell as many people as I possibly can to buy from someone else. I dont even care about the gm discount which I qualify for anymore, I am done!! I have been a loyal gm owner ofr years, but they really pissed me off now.... Good luck everybody.
  • natesmsnatesms Member Posts: 20

    Do you have the 4.10 gears in yours? I know there is a package that has the 6.0 with the 3.73's. The Max package puts in the 4.10's. I turn about 2300 RPM at 70mph. The 5.3 with 3.73s I test drove turned 1900 - 2000 at 70mph.

    I must say that aside from feeling the AFM kick on and off (my passengers don't notice it like I do, I think it has a lot to do with how closely I am paying attention to everything in my new truck), I really do like driving it around. I think if you want to tow an 8,000 pound boat comfortably you just have to accept paying the price at the pump, or pay the price on the sticker and get the diesel.

  • mule4mule4 Member Posts: 36
    ponch1 I was a die hard gm, ford & dodge owner. Wouldn"t look at anything different.I had all kinds of problems with a new gm car & new truck.All they would say was all the problems were normal. knowing they were lieing.I own a truck now that gets 18.5 to 19.5 on freeway 70 mpg with cruise set & depends how strong wind is.It doesn"t have AFM.It has 381 hp 6 spd. trans.It will pull a 9500# trailer like a 3/4 ton but my tk. is 1/2 ton.I had one problem with it They fixed it with no problen at all.Great service dept.Good luck with your new truck.I have had with mine
  • sknabtsknabt Member Posts: 14
    "I do not understand where all the lousy mpg is coming from. I get an honest 18 on the fwy. at 70 mph, in cruise control. Maybe that is the key, having it on cruise control." - 1offroader

    I agree 100%.

    Don't own a 6L but I do own an '08 5.3L Sierra. Overall city/highway I'm up to 17.2 mpg. To get there I have to liberally use the cruise control. Don't do 70. Tend to set it to 65 and forget it. I even use cruise control around town when I know I'll be able to tool down the road a couple of miles.

    Even mild acceleration sets it to V8 mode. I find my foot on the petal isn't as efficient as the cruise control going up inclines and maintaining speed. On flats cruise control spends the majority of the time in V4 mode. Naturally, when going down even gentle grades cruise or no cruise you'll get great mpg in V4.

    I haven't reset the command control to see how much I get just on the highway but looking at the instant fuel economy display I'd estimate 19-21 mpg.

    The downside is around town going stoplight to stoplight it's hard to get decent gas mileage. I tend to press the petal briefly to maintain speed then drift a bit, etc. But it depends on traffic.
  • chainlinkchainlink Member Posts: 3
    Good Lord: all these probs with the afm in these new mod has convinced me jus to put a new block in mine when she's done. I have the 99 new body z\71 4x4 and have loved every minute behind the wheel,with almost 300 thou she has been without a doubt the best truck I have ever owned.3 foot of mud or flat out like a lizzard she performs like a dream,and at a mer $2,3000.yep a new 5.3 block is in my future. :shades:
  • 1offroader1offroader Member Posts: 208
    I have the 3.73 gears, and 6.0L. I am not towing a huge trailer or boat and don't need the 4.10s. Yes, the Max Trailering package has the 4.10s.
  • 1offroader1offroader Member Posts: 208
    Chevy has sold perhaps 100,000 Silverados with AFM and there are what, 27 posts about problems??? And several of those posts have been by the same person. Do you consider that a sign of a major problem?

    I'm sure you've got a fine truck but I don't think 27 posts is excessive considering the tiny fraction of 1% with problems, do you? If there was a vehicle out there that sold 100,000 units and there were 100 problems (0.1 %) would you not buy it?

  • natesmsnatesms Member Posts: 20
    I agree with 1offroader. Given the volume sold and the small number of posts I think overall most poeple are happy with their purchase. Even with all the talk about how great the Toyota's are, if you look through that forum there is gripping going on there as well. I was amazed to see there were multiple people reporting getting the motors replaced due to "loud knocking engine noise".

    I'm getting used to the AFM "kick" and don't really notice it that much anymore. I'm also averaging 12.5 in the city now, which given rounding and factoring in that is very cold and remote start has made my list of top 5 best things ever, is excatly what the window says.

    I have a 550 mile trip this weekend. I'll reset the average and let you all know what I get at highway speeds. I don't believe I have the will power to not do at least 5 over the speed limit so I expect it to be pretty crappy at 75 mph.

    Another question pertaining to fuel mileage. Does anyone know if you get worse milage when you have the 4X4 set to auto (assuming it isn't engaged all the time)? I can hear something moving when you switch it to that mode, so I'm assuming that you are turning more "stuff" and hence decreased milage.
  • mule4mule4 Member Posts: 36
    About the small number of posts about the problems don't mean anything. The larger number of people don't post on these forums. lots of people that have trouble with their trucks have been told it's normal & they believe it .
  • gaspasser2gaspasser2 Member Posts: 44
    I doubt 100,000 owners are even aware of this forum. Just my .02. But I do hope its not as bad as you said.
  • natesmsnatesms Member Posts: 20
    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 Member 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.

  • fhainesfhaines Member Posts: 7
    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.
  • fueledupfueledup Member Posts: 64
    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.
  • fhainesfhaines Member Posts: 7
    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:
    http://www.motortrend.com/features/112_0609_2007_chevrolet_silverado/options.htm- 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.
  • fueledupfueledup Member Posts: 64
    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.
  • doc_holidaydoc_holiday Member Posts: 2
    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 Member 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 Member 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'.......my 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!!
  • tomkronbergertomkronberger Member Posts: 1
    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 Member 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 Member Posts: 2
    in your vehicle info on the dash it has an area to see the instant mpg and 4 or 8 cyl!
  • gmax6gmax6 Member 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.
  • rednecktroyrednecktroy Member Posts: 8
    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 Member 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 Member 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.
  • rednecktroyrednecktroy Member Posts: 8
    Is there anyone with the programmer in central Ohio? thanks Troy.
  • branhapbranhap Member 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. gm-trucks.com seems to have the most info on tuners.

    Good luck!

  • puttercaputterca Member 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 Member 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.
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