Last post on Aug 05, 2013 at 1:12 PM
You are in the Chevrolet Silverado & GMC Sierra
What is this discussion about?
Chevrolet Silverado 1500, GMC Sierra 1500, Chevrolet Silverado 2500, Fuel Efficiency (MPG), Truck
#38 of 85 Re: poor fuel mileage [fp2tall]
Jan 05, 2012 (1:24 pm)
I'm glad to see i'm not the only one with this problem. Maybe if more people with "Active fuel Management" problems would post their problems on this site, GM might actually start believing their really is a problem! Mine has over 5000 miles and it's not any better at all.
Thanks for your input.
#39 of 85 poor fuel milage 2011 silverado
Mar 30, 2012 (12:33 pm)
Purchased a new 2011 Silverado 02/03/2012 now have 66xx miles have had to dealer twice this week for poor mileage, (has always been bad but read posts and gave it time to break in). I averaged 14.6 mpg on the truck on a trip from Marble Hill, Mo to Corpus Cristi, TX and return.The service manager has done 2 "fuel Efficiency tests" (70 mph) first one was 15.2 mpg second one was 15.0 . The truck is throwing no codes so GM says nothing is wrong, GM suggested I take off bug shield, which I did today (which according to GM the bug shield is changing the aerodynamics of the truck causing the bad mileage), I am supposed to take truck back to dealer Monday 04/02/2012. I just wish GM would man up and fix the problem.
#40 of 85 Re: poor fuel milage 2011 silverado [smurf57]
Apr 02, 2012 (5:48 am)
I'm sorry to read that you are not 100% satisfied with your Silverado at the moment, smurv57. Looking forward to hearing how your visit to the dealership goes today.
All the best,
GM Customer Service
#41 of 85 Re: poor fuel milage 2011 silverado [smurf57]
Apr 02, 2012 (8:36 am)
I've had the same problem as you since day one on my 2011 Crew Cab Silverado 5.3 six speed trans. My advise to you is, try not let one of GM's engineers look at your vehicle. He will only confirm that there are no detectable trouble codes. That info will then be tagged to your VIN number. Once that happens, none of the dealerships will check your truck without getting GM approval. GM will then deny there is a problem and refuse to do anything related to that problem because there is no trouble code. This lets everybody off the hook, except you, holding the bag! Effectively, that voids your warranty as far as anything related to that problem, sneaky huh!. If you look at your Inst. fuel economy (DIC gauge) , most likely you will see that your engine's "Active Fuel Management" is not working at normal highway driving speed (around 70 MPH, when most needed). That is where you can see when the engine changes from v8 to v4 mode (that does not trip a trouble code when not working correctly). I have read that ithis is mostly a problem with the 5.3 Vortec engines with the six speed transmissions. I think if GM wanted to fix the problem, they would recalibrate the vehicle computers for that model truck. Good luck! Just wait till you hear all the ridiculous excuses they give you.
#42 of 85 Re: poor fuel milage 2011 silverado [string2]
Apr 02, 2012 (9:27 am)
HALF TRUTH ALERT!
String the AFM isn't working IN YOUR TRUCK. It's working in the other half million units on the road. My truck included. I can consistently get 20mpg at 70ish with the AFM activated on the highway.
#43 of 85 Re: poor fuel milage 2011 silverado [chuck1]
Apr 02, 2012 (1:41 pm)
Okay Lucky! Go ahead and rub it in! We know yours works like it's suppose to. The only way you could be getting 20 mpg is for your AFM to be working in v4 as it should at hwy speed. But I would like to know how you came up with those conclusive facts that every GM truck, but mine, works like yours and is averaging 20+ MPG.
There are many, many GM truck owners who have never visited any website. There are at least 14 reported posts on this website that say they are also having problems, not to mention complaints on other websites or those that didn't post their complaints at all. I know how they are supposed to work (like yours). All these trucks should get that kind of gas mileage. However, I think you have to agree, these complaints should represent a considerable number of problem GM trucks on on the road.
You have helped to make the point for me and the other problem GM truck owners though. As you have just acknowledged, yours is operating normal!
GM tells me mine is working normal at 16 MPG on flat highway 65 70 MPH without the AFM working at all. AND, they won't try to fix it.
By the way Chuck, does your truck have 6 speed transmission or 4 speed automatic trans.
#44 of 85 Re: poor fuel milage 2011 silverado [string2]
Apr 02, 2012 (2:44 pm)
"By the way Chuck, does your truck have 6 speed transmission or 4 speed automatic trans"
The "clunky" six speed. (Yea, mine clunks too!)
#45 of 85 Poor Mileage / surging / clunking / heavy heavy soot and chevy regret
Oct 23, 2012 (5:58 pm)
Purchased my 2011 Silverado 1500 LTZ Crew Cab October of 2011. The first 7000 miles were at 17.7 miles to the gallon. AFM worked perfectly. About 7500 miles the voltage guage started doing the dip below 14v on the guage, and I noticed the trucks mileage started dropping. Then the misshifts, hesitations, coughing, started. I also noticed how HOT my garage was getting after parking the truck in it, you could hear the tinging of the metal cooling down from the exhaust system. I had mentioned the poor running condition to the dealer and was told it was probably bad fuel. I choked on this for a while, and then the soot on the tail pipe started as the mileage dropped. Complained, to no avail, normal normal. .... Labor Day 2012, I bring the truck in and say no more, something is wrong. No codes, but they noticed that the Alchohol content is reading 0% all the time, and the fuel in the truck is 15% Alchohol. They re-learn the Alchohol content, and the truck is normal until the very next tank, which happens to be Ethanol free fuel. Im back to the poor running condition again.
Fast forward to 14k miles. Im down to 13.3 MPG, clunking all the time, and its surging like Im being rear ended. This truck does not like to coast at all, resuming any acceleration causes it to hesitate.
Service department says that they see what my complaint is, but cant fix anything because corporate says its working as designed and wont let them do anything. This "anomale" only happens to be on the 2011 1500 AFM product line. Thing is, they say the delay they put in the accelerator is normal, and its to save all the torque from being dumped on the transmission. Obviously with it the hesitation getting worse, the torque placed on the trans (the clunking), the worse the trans gets.. how is this delay or hesitation helping my transmission again GM ???? 46,000 dollar Mistake is all I keep saying to myself, should have kept the 2006 Ford that got a consistant 15 MPG towing or solo. This is the Last GM product I will ever buy with this kind of lack of integrity from Corporate. Obviously reading here, there are alot of other people that are having the same exact issue with their trucks ...... if anyone is watching, I would love to know what gear ratio the trucks with this issue are equipped with.... Mine has the 3.42's ???????????
#46 of 85 Did they tell you it's normal?
Oct 23, 2012 (8:18 pm)
About 7500 miles the voltage guage started doing the dip below 14v on the guage, and I noticed the trucks mileage started dropping.
The alternator has a energy saving feature that turns it down when the system is not needed.
#47 of 85 Re: Did they tell you it's normal? [chuck1]
Oct 23, 2012 (8:58 pm)
Not needed ??? when has 9V been the same as 12V ??? If you have ever wrenched before, and changed an alternator, battery or starter, you will see that the manufacturer or re-manufacturer states Voltage must be 12.7 for them to guarantee their parts. Starter manufacturers would prefer you replace the battery at the same time as the starter....
Of course its normal, Im well aware of the alternator doing this, we have a 2007 and 2008 3500 Duramax, 2010 1500 LTZ, 2011 1500 LTZ ( this one ) and a 2012 1500 LT, so Im well aware of the issues of these trucks, Im saying that my PCM has probably more issues since this voltage drop, and trust me as much as that needle drops, it also pegs max out to the top of the line they drew so that they dont have to explain this "feature" , they can point and say "NORMAL" just like everything else is "normal"
GM tends to take a great idea and over complicate it. What possible mileage gain can be seen thru turning off an alternator ??? That same gain gets lost when it has to work twice as hard to pump up a weakened battery. Also, my power inverter HATES this voltage drop and will not power up my laptop on trips as the voltage is too low, as it sees that as a battery drain .. Dealer says ... so what, its not our power convertor and wasnt sold as a chevy option......
As a computer technician, I can tell you how many PC power supplies in both desktop and laptop computers I replaced due to faulty power supplies. Problems disappeared once the computer got "clean" stable power. Computers that are underpowered get unpredictable, and you cant tell me an automotive PCM is not the same as a regular computer, its more of a specific task oriented device... but they are pretty much the same animal running on the same 12V DC platform.
What amazes me is, Our $46k cars are not our own anymore, the corporation still owns them and will tell you how they are supposed to run and deny any claim if they can pin it on something else....... In this case, the delay they say should be there is .006 sec upon stepping back on the throttle, and Im saying its a full 3.0 seconds, thats a HUGE difference, one that can be felt most of all about 20- 35 MPH ( school zones, traffic conditions, curvy roads ) and YES, the dealer READ verbatim the blurb from GM about the .006 second delay ...... his response was to stop "tromping" on the gas pedal, well you cant tromp on the pedal in bumper to bumper traffic !!!!!!!!!!!
OH !!!!!!!! yes, I was also told the heavy soot on the tailpipe was caused by a non GM chrome tip on the exhaust, to my reply of - its part of the Z71 chrome package shipped out from the factory with it on.... stopped him dead in his tracks on that, but he said he would check for a "bulletin"