C7 engine vibration with AFM
Thread Starter
Heel & Toe
Joined: Sep 2009
Posts: 15
Likes: 1
From: San Diego, CA.
C7 engine vibration with AFM
When my C7 enters the 4 cylinder mode the engines vibrates much more than I feel that it should. I have built quite a few engines over the years and this just doesn't seem right. The Chev dealer mechanics just tell me that it isn't that bad. My question is: does anyone else have the same problem (or perhaps it is normal)?
Pro
Joined: Jul 2004
Posts: 681
Likes: 39
From: Columbus Indiana
When my C7 enters the 4 cylinder mode the engines vibrates much more than I feel that it should. I have built quite a few engines over the years and this just doesn't seem right. The Chev dealer mechanics just tell me that it isn't that bad. My question is: does anyone else have the same problem (or perhaps it is normal)?
FWIW: my M7 car, I can only sense the increased vibration if I rest my hand on the shift lever. Otherwise, it's totally transparent.
Thread Starter
Heel & Toe
Joined: Sep 2009
Posts: 15
Likes: 1
From: San Diego, CA.
I have a manual shift and I can feel it most thru the shifter but also on the steering wheel and the some thru my feet on the floor. My worry is what is this going to do the engine components after the extended warranty runs out. If one of the engines that I have built in the past had that much vibration I would tear it down again and have it balanced. The first time that I experienced the vibration it startled me and I let off the gas thinking that something had gone wrong. Chevrolet as of yet has no opinion. Their comment is that the C7 is so new that they don't have enough experience yet. Terrible service from a major dealer.
Le Mans Master
Joined: Aug 2006
Posts: 5,873
Likes: 5
From: Michigan
I can feel it in the wheel slightly. Not really a big concern of mine. I like the extra mpg I get on a long trip though !
Where I really dislike the afm is when you get off the gas then get on the gas in let's say sixth at 65-70 I've had it lurch before a few times as it goes back into 8cyl under load.
I just switch it to tour when I have these situations now.
Where I really dislike the afm is when you get off the gas then get on the gas in let's say sixth at 65-70 I've had it lurch before a few times as it goes back into 8cyl under load.
I just switch it to tour when I have these situations now.
Le Mans Master
Joined: Jun 1999
Posts: 5,059
Likes: 11
From: Wenatchee WA
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
I can feel it in the wheel slightly. Not really a big concern of mine. I like the extra mpg I get on a long trip though !
Where I really dislike the afm is when you get off the gas then get on the gas in let's say sixth at 65-70 I've had it lurch before a few times as it goes back into 8cyl under load.
I just switch it to tour when I have these situations now.
Where I really dislike the afm is when you get off the gas then get on the gas in let's say sixth at 65-70 I've had it lurch before a few times as it goes back into 8cyl under load.
I just switch it to tour when I have these situations now.
Burning Brakes
Joined: Dec 2013
Posts: 1,051
Likes: 302
My Z51 M7 lurches too when it goes into V8 mode from V4, and slightly less when it goes into V4 mode. However I have no real vibration issues in either mode. Idle is a little rough though. But on the highway engine and drivetrain is smooth in both V4 and V8 modes. So I would say it is not normal to have vibration that is bothersome in V4 mode.
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Burning Brakes
Joined: Feb 2010
Posts: 878
Likes: 61
From: Louisa, Ky
Yes mine does it too! Especially light pedal driving about 30 mph. The switching drives me crazy and its terrible trying to come out of V4 mode because the requirements of the road or upshift has occurred. First I hear garbled exhaust, then the vibration and loss of throttle response until it switches to V8 or I hasten it by pushing the thottle on down. The only mode on mine to avoid this is M on shifter. I was surprised by this and think it should be programmed out of at least half of the modes. Even in Track mode with light pedal it goes to V4 and slams the exhaust shut about 30 mph. No problem when you drive it like you stole it!
Burning Brakes
Joined: Feb 2010
Posts: 878
Likes: 61
From: Louisa, Ky
On mine only putting shifter in M eliminated V4 mode its does it in all modes in drive position. Needs refinement on mine, something I will deal with when everyone gets up to speed at local dealers. Or next trip to Bowling Green Function where Engineers are available to talk to.
Team Owner
Joined: Sep 1999
Posts: 20,054
Likes: 44
From: Swansea IL
I wonder if GM engineers will start tweaking the "parameters" of how/when the AFM is engaged and provide software updates as more and owners start providing real world feedback. Personally I think the system should be functional ONLY in Weather, Eco and Tour modes and disabled in SPORT/TRACK modes (regardless of transmission modes). That sure sounds like an easy software update to me.
But unfortunately I believe that feedback needs to come from dealers responding to owner complaints and actually bringing their cars into the dealer for investigation where they are charging GM for warranty labor?
So maybe we need to start taking our C7’s to our local dealers complaining about AFM.
But unfortunately I believe that feedback needs to come from dealers responding to owner complaints and actually bringing their cars into the dealer for investigation where they are charging GM for warranty labor?
So maybe we need to start taking our C7’s to our local dealers complaining about AFM.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,821
From: Charlotte, NC (formerly Endicott, NY)
Two weekends ago I spent several hours driving my son's Z51 with the manual shift. The drive train vibrated when the system went into 4 cylinder mode and I could feel it the same way you do. I believe this is natural to the system due to 4 cylinders not firing. Yes, the valves are closed and they are just compressing air and then using the air pressure to help push the piston down but there is a power drain on the other 4 cylinders which can make the engine vibrate similar to a misfire situation. I am basically in the "They all do it" camp. I found when running in eco mode that the gas mileage was excellent and well worth putting up with a little vibration at times.
Bill
Bill
7th Gear
Joined: Jul 2014
Posts: 7
Likes: 0
Two weekends ago I spent several hours driving my son's Z51 with the manual shift. The drive train vibrated when the system went into 4 cylinder mode and I could feel it the same way you do. I believe this is natural to the system due to 4 cylinders not firing. Yes, the valves are closed and they are just compressing air and then using the air pressure to help push the piston down but there is a power drain on the other 4 cylinders which can make the engine vibrate similar to a misfire situation. I am basically in the "They all do it" camp. I found when running in eco mode that the gas mileage was excellent and well worth putting up with a little vibration at times.
Bill
Bill
Banned Scam/Spammer
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Melting Slicks
Joined: May 2008
Posts: 2,606
Likes: 355
From: Rochester New York
You will get a minor vibration from AFM. The installation of long tubes will make it worse. If it does not seem "minor" to you, I recommend trying a different dealership's service department.
Thread Starter
Heel & Toe
Joined: Sep 2009
Posts: 15
Likes: 1
From: San Diego, CA.
I really want to once again thank everyone that responded to my AFM issue. It was "very" helpful to hear from other C7 owners. I ended up replacing the motor mounts with an after market from a Corvette racing shop that I deal with. We did the job in about three hours (using his equipment). The vibration is still there but it is much, much less and I am now a happy camper again. Thank you all.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
On my C7 the AFM is almost seamless---
1st question Is your exhaust STOCK ? or did you have someone put a cat-back system on ?
Reason I ask---These cars may or may not have NPP exhaust HOWEVER ----IF you look under the car you can see the NPP AFTER the mufflers---BUT BEFORE the mufflers there is another set of butterfly valves on the exhaust !!!!! These butterflies are supposed to almost CLOSE COMPLETLY SHUT when AFM is activated---
Many exhaust guys don't know what they are for and cut them out thinking it will give them less restriction--Not the case--!!!
ALSO when my car was 1st new---I could hear the butterflies NOT closing and it sounded weird and felt jerky---After about 200 miles they started working perfectly and now as I said it is seamless---reason unknown could be from sitting long or moisture or new car debris sorta jammed them open
1st question Is your exhaust STOCK ? or did you have someone put a cat-back system on ?
Reason I ask---These cars may or may not have NPP exhaust HOWEVER ----IF you look under the car you can see the NPP AFTER the mufflers---BUT BEFORE the mufflers there is another set of butterfly valves on the exhaust !!!!! These butterflies are supposed to almost CLOSE COMPLETLY SHUT when AFM is activated---
Many exhaust guys don't know what they are for and cut them out thinking it will give them less restriction--Not the case--!!!
ALSO when my car was 1st new---I could hear the butterflies NOT closing and it sounded weird and felt jerky---After about 200 miles they started working perfectly and now as I said it is seamless---reason unknown could be from sitting long or moisture or new car debris sorta jammed them open
