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Chevy Silverado and GMC Sierra Active Fuel Management Problems
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
See Also: GM's Active Fuel Management and Oil Consumption Issue
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Comments
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.
1offroader
Whew, glad I found this thread, cuz till now, my 6.0 has been running flawlessly.
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.
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.
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.
1offroader
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.
tafid
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.
1offroader
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!
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.
tafid
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:
1offroader
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.
natesms
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.
natesms
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.
1offroader
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.
natesms
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.
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.
1offroader
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?
1offroader
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.
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.
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.
tafid
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.
"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.
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.
also any suggested ideas on what to do when the truck doesnt start when it's cold or hot, mostly cold ?
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!!
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.
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.
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.
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!
Paul
I had the same frustrations as you and learned that this could be done very easily.