gary92109

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)?

cam30era

Manual or automatic trans? How do you sense it? i.e. through hand on shifter, steering wheel, or "seat of the pants"?

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.

gary92109

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.

Waytofastvette2006

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.

Road_runner

Tour eliminates 4 cylinder mode?

cam30era

With the M7, every mode is V8 only except Eco.

descartesfool

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.

gary92109

thank you for your info replies. Nice to hear from other owner/drivers

Jim Barker

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!

Jim Barker

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.

AFVETTE

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.

Bill Dearborn

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

cosmicdust73

I read somewhere that the AFM switching vibrations is what is leading towards the torque tube failures due to excessive bearing wear. I'll find out tomorrow if I need my torque tube replaced after only 7k miles on a 6AT.

faninc

Diablo tuner can disable AFM...

n8dogg

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.

gary92109

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.

tblu92

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

3 Z06ZR1

On my C7 AFM is disabled and I still see 28.3 as best average!

TEXHAWK0

Guess I will never know if my C7 has a vibration in 4 cyl. mode.

faninc

I get 30 MPG HWY with NO AFM...