AFM v4 mode question
Thread Starter
5th Gear
Joined: Jan 2020
Posts: 5
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AFM v4 mode question
Hi everyone I’m brand new to this forum and the corvette community and I’m actively looking for a corvette around March 
. My ideal car is a 2016-17 c7 stingray coupe 8spd z51. I’ve been doing a lot of research for the past two years on this car in preparation of getting one and I’m seeing a lot of concerns with the AFM v4 mode cylinder issues and I’m trying to not fall victim to that. I know that id be able to buy a range AFM disabler but I’m concerned with the lasting effects this might have? How often are these c7s affected by this issue ? Is this something I should basically be prepared to fix when buying this car ? I’d like to make my first purchase to be a great experience and not spend more money to fix parts because of this issue.
Anything helps. Thanks all!!!
. My ideal car is a 2016-17 c7 stingray coupe 8spd z51. I’ve been doing a lot of research for the past two years on this car in preparation of getting one and I’m seeing a lot of concerns with the AFM v4 mode cylinder issues and I’m trying to not fall victim to that. I know that id be able to buy a range AFM disabler but I’m concerned with the lasting effects this might have? How often are these c7s affected by this issue ? Is this something I should basically be prepared to fix when buying this car ? I’d like to make my first purchase to be a great experience and not spend more money to fix parts because of this issue.Anything helps. Thanks all!!!
Last edited by TDay1995; Jan 25, 2020 at 10:02 AM.
Le Mans Master
Joined: May 1999
Posts: 6,514
Likes: 1,301
From: Windermere FL
There are no long term effects to using the Range, other than a small drop in MPG. The LT1 should never had DoD!
As far as buying an A8 C7 or any other GM with the A8, yes, the car can indeed develop the dreaded shudder eventually. Usually, just after the power drive warranty expires!
As far as buying an A8 C7 or any other GM with the A8, yes, the car can indeed develop the dreaded shudder eventually. Usually, just after the power drive warranty expires!
Thread Starter
5th Gear
Joined: Jan 2020
Posts: 5
Likes: 0
There are no long term effects to using the Range, other than a small drop in MPG. The LT1 should never had DoD!
As far as buying an A8 C7 or any other GM with the A8, yes, the car can indeed develop the dreaded shudder eventually. Usually, just after the power drive warranty expires!
As far as buying an A8 C7 or any other GM with the A8, yes, the car can indeed develop the dreaded shudder eventually. Usually, just after the power drive warranty expires!
Understandable. That being said. How can I tell if this issue is present ? I’ve heard popping it into neutral and seeing if the shudder stops (if shudder is present) are there other early warnings that I can see? And how would I go about getting the dealer to detail if these issues exists?
And by popping the sensor on with the present issue won’t fix it but I’d assume it’s recommended to fix the issue if it’s there and then pop the sensor on ?
Thanks again.
Le Mans Master
Joined: May 1999
Posts: 6,514
Likes: 1,301
From: Windermere FL
The dealer can hookup electronics to measure the exact slippage. There are many posts in the sticky thread that detail how a dealer can measure it. Used to be, GM would require the dealer to perform this mesaurement before doing the latest triple flush but now GM does not require it. If the shudder is severe enough, you can actually see the RPMs fluctuate on the tach when it goes into V4 mode. If you got the full shudder, it feels just like riding over rumble sticks when the road is flat and smooth. Bone jarring is a good way to describe it.
In some cases, the Range can 'mask the shudder, and if it is too sever it will not. Most of the time that means you needa new torque converter, and the tranny has to be dropped. Lots of pictures of the major surgery involved with that in the sticky I think. I would hate to have to foot the bill for that outside of warranty!
In some cases, the Range can 'mask the shudder, and if it is too sever it will not. Most of the time that means you needa new torque converter, and the tranny has to be dropped. Lots of pictures of the major surgery involved with that in the sticky I think. I would hate to have to foot the bill for that outside of warranty!
Thread Starter
5th Gear
Joined: Jan 2020
Posts: 5
Likes: 0
The dealer can hookup electronics to measure the exact slippage. There are many posts in the sticky thread that detail how a dealer can measure it. Used to be, GM would require the dealer to perform this mesaurement before doing the latest triple flush but now GM does not require it. If the shudder is severe enough, you can actually see the RPMs fluctuate on the tach when it goes into V4 mode. If you got the full shudder, it feels just like riding over rumble sticks when the road is flat and smooth. Bone jarring is a good way to describe it.
In some cases, the Range can 'mask the shudder, and if it is too sever it will not. Most of the time that means you needa new torque converter, and the tranny has to be dropped. Lots of pictures of the major surgery involved with that in the sticky I think. I would hate to have to foot the bill for that outside of warranty!
In some cases, the Range can 'mask the shudder, and if it is too sever it will not. Most of the time that means you needa new torque converter, and the tranny has to be dropped. Lots of pictures of the major surgery involved with that in the sticky I think. I would hate to have to foot the bill for that outside of warranty!
oh dang, that sounds expensive
I’m starting to reconsider if I want a corvette now. Does this occur around a certain mileage? Meaning if I’m buying used how many miles should I take into consideration to see if that car has experienced the issue and/or been replaced ?
Le Mans Master
Joined: May 1999
Posts: 6,514
Likes: 1,301
From: Windermere FL
You have many chooses.
- Buy an M7 and never have to worry about it at all!
- Buy an A8 that still has some bumper-to-bumper left on it and then buy a GM supplemental warranty from Dennis on this forum to extend the drivetrain warranty for as many miles and years that you think you will keep the car.
- Wait a few months and look at buying an C8 and see what issues the DCT might have.
Thread Starter
5th Gear
Joined: Jan 2020
Posts: 5
Likes: 0
You have many chooses.
- Buy an M7 and never have to worry about it at all!
- Buy an A8 that still has some bumper-to-bumper left on it and then buy a GM supplemental warranty from Dennis on this forum to extend the drivetrain warranty for as many miles and years that you think you will keep the car.
- Wait a few months and look at buying an C8 and see what issues the DCT might have.
In regards to the M7 I haven’t driven a manual before and wouldn’t want my first real sports car to be a Manual bc I don’t wanna have any issues with the clutch.
Racer
Joined: Nov 2015
Posts: 260
Likes: 87
From: Brighton MI
OP - You will get many responses on this & will need to filter out what applies to you. We have a 2016 Z51 & last September had the dealer install the latest ATF (Mobil 1 Syn LV ATF HP 124715). We also have the Range Disabler installed which prevents going into AFM mode. I'm very happy with this setup.
The AFM design targets for a 10 RPM slippage when in V4 mode. IMHO this is a very tight & difficult window to maintain & it appears that when the RPM slippage is greater than the intended 10 RPM shudder can be induced. Prior to installing the latest ATF last fall & w/o Range disabler I was seeing the tach vary about 50 RPM when in V4 mode. I have not evaluated slippage in V4 mode since then as I've been running the Range Disabler. I will do this when vehicle comes out of hibernation in the spring.
In summary, I would ask any seller of a vehicle you're looking at what they have done since they've had it. In essence, I wouldn't be too concerned with purchasing a used vehicle if you have the complete story & evaluate yourself.
Good luck.
The AFM design targets for a 10 RPM slippage when in V4 mode. IMHO this is a very tight & difficult window to maintain & it appears that when the RPM slippage is greater than the intended 10 RPM shudder can be induced. Prior to installing the latest ATF last fall & w/o Range disabler I was seeing the tach vary about 50 RPM when in V4 mode. I have not evaluated slippage in V4 mode since then as I've been running the Range Disabler. I will do this when vehicle comes out of hibernation in the spring.
In summary, I would ask any seller of a vehicle you're looking at what they have done since they've had it. In essence, I wouldn't be too concerned with purchasing a used vehicle if you have the complete story & evaluate yourself.
Good luck.
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Pro
Joined: Aug 2010
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From: Rock Hill S.C.
I wouldn't let the A8 problem stop you from getting a C7. We only see the posts that have the problem which is a small percentage of A8's Many of us have been trouble free but I would definitely invest in a range device.
Thread Starter
5th Gear
Joined: Jan 2020
Posts: 5
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i think your right and I agree. My biggest concern is I buy the 2016 and the warranty is expired what happens if I have this issue? I’m 24 and have been saving money for quite some time now though my job does pay well so being able afford a great car isn’t an issue but having a potential engine fail or a trans break is very frightening to me if there isn’t a warranty on it and with it being 2020 now idk if they are still applicable :/
Burning Brakes
Joined: Oct 2014
Posts: 1,057
Likes: 339
What system would that be? Ain’t even the same transmission. No one knows if they’ll slip the clutch like they do on the TCC on the A8 to reduce driveline NVH. We won’t know how well this DCT performs until quite a few are sold and running around for a while.
Last edited by KemahGT; Jan 28, 2020 at 04:56 PM.
Team Owner
Joined: Sep 2001
Posts: 62,139
Likes: 1,728
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
C8 does not use the same transmission at all.
Put in a Range device, leave it in forever, and do not worry about the TC issue. Otherwise get a stick shift.
The TC issue is due to the engine dropping in V4 mode, the triple flush and new fluid raises the viscosity to mask it or delay its failure. If you never get to V4 mode, it shouldn't happen, so leave the Range in.
Put in a Range device, leave it in forever, and do not worry about the TC issue. Otherwise get a stick shift.
The TC issue is due to the engine dropping in V4 mode, the triple flush and new fluid raises the viscosity to mask it or delay its failure. If you never get to V4 mode, it shouldn't happen, so leave the Range in.