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Vibration When Afm Puts Truck In 4 Cylinder Mode


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I am experiencing a pretty bad vibration in my 2011 Avalanche LTZ 4x4 when my AFM puts my truck into 4 cylinder mode. It's noticeable at most speeds but I would say more noticeable at low speeds when trying to maintain that constant speed. It really vibrates the truck badly. I can feel it in the gas pedal and seat mainly but it is noticeable in other areas as well. The truck drives great with non issues when in V8 mode. Is anyone else experiencing this issue with their active fuel management equipped vehicle? Is there a fix? This can't be normal!! GM techs please feel free to chime in.

 

Thanks

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Sounds like the wrong four cylinders are firing in the fuel saving mode. I would not drive it in that position until you figure it out. Before I spent much time and effort on this, I'd be talking to the dealer about replacing the truck if it can't be fixed in a timely manner.

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I would get it back to the dealer ASAP. What you describe is not normal. I can't tell any difference on mine between 4 and 8 cyl. If not for the DIC saying it's in 4 cyl I would not know. Let us know what you find out.

 

Same here. I can't tell if I don't look at the dash.

 

And I no longer leave that display up, as when it's on, I can't stop staring at it. :lol:

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I would get it back to the dealer ASAP. What you describe is not normal. I can't tell any difference on mine between 4 and 8 cyl. If not for the DIC saying it's in 4 cyl I would not know. Let us know what you find out.

 

 

I dropped it off this morning to have it looked at. It only has 500 miles on it. The shop foreman took a ride with me and he too felt the vibration. We went back to the dealer to drop it off. While inside I overheard one of the gentleman saying that the vibration in the AFM is NORMAL. Whatever. I've owned a 2007 and 2010 Avalanche and had no problems with any of them. I am expecting the answer to be "normal characteristic"....so, I have already contacted GM Corporate office and spoke to a nice lady that is going to help me once I get an answer from the dealer. Anyone else out there with any good information in regards to my issue, please post...

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The AFM transition is pretty much seemless. I have found a few odd ball driving instances that I have felt a slight droan or hum from 4 cylinder mode but never a severe vibration.

 

Is there any engine speed vibration felt at ALL in 8 cyl mode? Might be 4 cyl mode just exaggerating the vibration.

Nothing really, in 4cyl mode change, that should cause a vibration other than the load on the engine is increased due to half of the cylinders not firing.

Edited by ChevyTech77
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The AFM transition is pretty much seemless. I have found a few odd ball driving instances that I have felt a slight droan or hum from 4 cylinder mode but never a severe vibration.

 

Is there any engine speed vibration felt at ALL in 8 cyl mode? Might be 4 cyl mode just exaggerating the vibration.

Nothing really, in 4cyl mode change, that should cause a vibration other than the load on the engine is increased due to half of the cylinders not firing.

 

 

The truck drives great in 8 cyl mode. No vibrations at all....only in 4 cylinder mode. I know the owners manual says the transition is seemless, but I can tell you anytime it switches and what mode it is in without looking at DIC. Thanks for your reply and help.

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The truck drives great in 8 cyl mode. No vibrations at all....only in 4 cylinder mode. I know the owners manual says the transition is seemless, but I can tell you anytime it switches and what mode it is in without looking at DIC. Thanks for your reply and help.

 

Yup, something defienently wrong then. What exactly, hard to tell to be honest but I hate to say it, might be

something internal in the engine.

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The truck drives great in 8 cyl mode. No vibrations at all....only in 4 cylinder mode. I know the owners manual says the transition is seemless, but I can tell you anytime it switches and what mode it is in without looking at DIC. Thanks for your reply and help.

 

Yup, something defienently wrong then. What exactly, hard to tell to be honest but I hate to say it, might be

something internal in the engine.

 

 

 

ChevyTech77, are you a GM Technician? If so, have you ever seen this issue before?

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ChevyTech77, are you a GM Technician? If so, have you ever seen this issue before?

Of 15 years, yes and no, I have not.

 

 

 

Thank you. I hope to hear something back from the dealer today. If they state it is normal, what do you suggest my next step be?

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Thank you. I hope to hear something back from the dealer today. If they state it is normal, what do you suggest my next step be?

 

Talk with the service manager. If he is of no help, contact the GM Customer Assistace Center.

 

Hope it works out. :rolleyes:

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The dealer called me back and said that everything checks out ok on their end. They say there are no codes, etc. being trown. I mean how can a vibration "check out ok"? They are going to contact service assistance or something like that in detroit to see what they have to say. The no codes.....i mean the codes, i think, are only thrown if the computer senses something that is not pre-programmed to happen in the computer?? Can the dealer turn off the AFM?? If Detroit does not have anything good to say, then it is straight to NHTSA, BBB. I think if its normal then its a poor design on GM's part to make a vibration normal characteristic.

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The dealer called me back and said that everything checks out ok on their end. They say there are no codes, etc. being trown. I mean how can a vibration "check out ok"? They are going to contact service assistance or something like that in detroit to see what they have to say. The no codes.....i mean the codes, i think, are only thrown if the computer senses something that is not pre-programmed to happen in the computer?? Can the dealer turn off the AFM?? If Detroit does not have anything good to say, then it is straight to NHTSA, BBB. I think if its normal then its a poor design on GM's part to make a vibration normal characteristic.

It's really hard to tell you what's normal or not without driving your vehicle, understand that. I will repeat though, I

have noticed some weird vibes from AFM engines before when switching back and forth between modes. Nothing severe, like you state your's is, though.

 

Let your dealer work the case. No codes doesn't mean much, there can still be problems. If this is abnormal, when compared to a known good vehicle of the exact same build, then there is something wrong and it CAN be fixed. Be patient. If they can't get it repaired to your liking, contact GM as I stated earlier. NHTSA and the BBB won't do much for you but GM can.

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