NSC5

As mountainears stated an A8 equipped C7 (except for the ZR1 which doesn't have AFM) will go into V4 mode in any driver mode setting unless the vehicle is in manual, uses a Range anti-AFM module, or is tuned to remove AFM activation.

As expected there is a lot more vibration when an engine designed as a V8 is operating on only 4 cylinders. The steel torque tube used in some models is better at damping vibration so it is part of the solution but a lot of the vibration damping (and I believe A8 damage) occurs because GM also modulates the friction or "lockup" clutch in the torque converter on/off/on at a very rapid rate when in V4 mode to allow the fluidic coupling of the unlocked converter to operate as a very effective vibration damper. This use of the converter clutch results in accelerated wear and the current fluid has additional friction modifiers to help the clutch better survive this operation and the flush also removes the wear material from the fluid circuit.

Every time a cylinder fires there is a minute change in crankshaft speed (this is one of the methods modern engine controllers use to diagnose injector or other cylinder contribution issues in real time operation) and in V4 with half of the pulses per RPM of V8 mode the vibration will be more severe and of different frequency so vibration reduction strategies are necessary to avoid owner complaint. The M7 equipped Corvette was programmed differently to avoid this level of complaint and carbon fiber torque tube equipped Corvettes like my Z06 have less vibration damping AND the lower compression ratio of the supercharged engine has a smaller operating window where AFM is effective in saving fuel via V4 so even operated without a Range module it would seldom go into V4 mode which is why it is rare to see a Z06 with torque converter issues.

Zackbo

I have only been a member for a week but I can already tell NSC5 is a deep well of knowledge. I agree it's the cycling of the lockup clutch that is probably causing the damage.

I confirmed today that mine is doing the RPM jump thing. I can't feel it, but it's definitely there, and stops when I go into M. Not sure whether I should not worry about it and let it destroy itself while still under warranty or go ahead and order a Range.

Heidemarie

[QUOTE=Zackbo;1597051136]I have only been a member for a week but I can already tell NSC5 is a deep well of knowledge. I agree it's the cycling of the lockup clutch that is probably causing the damage.

Good info; watching closely.
Heidi
Save the wave

SRQStingray

kennyjames21

The thing is, I don't think its the transmission, I think its the AFM - the reason the M7 cars aren't having as many issues is because AFM doesn't kick in nearly as often as it does on the auto, that's also why you don't hear about it happening with Z06's with the A8 as much.

Zackbo

Does anyone here know if the 6th gen Camaro has the same torque converter? I'm sure it has the 'V4' mode also, and subject to the same vibrations. It seems if the failure rate was that high there would be an uproar with Camaro owners also, considering Camaro sales outnumber Corvette sales by almost 10:1.

SRQStingray

Brewskii

I Have a 2018 v6 Camaro.. an it is a beast !! even with track mode I burn out like its nothing.. cant imagine trying with track mode of I probably wouldn't even go anywhere ahhaha.. 335 hp v6.. I beat a lot of v8's because there fat an have no grip !!

The Brewskii signing out -

C5Driver

Everyone that owns an A8 should invest in the Range AFM module. It works well now but you must get the latest software version.

kennyjames21

The GM camaros and trucks that use AFM are having similar issues, go look in some of their forums. AFM is a disaster, plain and simple. Early on, engines were consuming oil (stopped me from buying a camaro a few years ago) because of it and now this.

NSC5

I was on the fence between going from my 2006 Sierra 2500HD to the 1500 series crewcab but the AFM issue was enough to get me to buy my third Duramax diesel which runs on all 8 cylinders all of the time as God intended

Dif

A lot depends on how much the RPM is fluctuating, especially if you cannot feel it shudder.
My 2016 A8 just turned 15,000 miles and I've had a slight shudder since new, but,.. not all the time.
And when it does do it, I only notice it at highway speeds in V4.
Any other time or speed in V4 it's not noticeable at all.
With Cruise control set to 70-80 mph in V4 I watched the RPM's with the DIC display set to Sport because the needle shows the RPM more accurately than the other displays.
And the RPM fluctuates up and down about 50-65 RPM's, then becomes steady if I put it in Manual mode.
The odd thing is, it seems to depend on the weather temperature and/or how warmed up the car is whether it shudders or not.
If I drive for a while and stop somewhere for 10 -20 minutes or more and drive again, the shudder is pretty much non existent.
It seems once everything is heat soaked before the car totally cools off, the TC works great in V4.

Recently I noticed the slight shudder, but it was a varied harmonic shudder which is something new.
So, I talked with my Dealer recently about it and having them check it out next week.
They have not done TC changes in the C7, but have done them in a few trucks.
But they've done the Flush procedure on a few C7's and if they feel mine is not right, they're going to do the Flush.
At this point since the shudder is not drastic or constant, I'd rather have the Flush done first to see if it makes a difference before having the car torn apart for a new TC.
Time will tell if it will need a new TC or not.
Just info for what it's worth

plake

I am new to this C7, just got mine, used C7 Coupe A8 with 5K miles. So far I cannot detect any of these reported issues but again new to this car. How can I see when it goes into V4 mode? I am really leaning toward getting the Range disabler, spoke with them yesterday and it sounds like the latest software has all the bugs worked out. They really stressed not buying it from a outside source, you may not get newest software. I don't want to have any of these issues. I remember back when Cadillac came out with the 8, 6, 4 BS, was a disaster, now AFM.

Squeaky Wheel

On one of the dash displays (forget which one off hand) it will show you how many cylinders are active. Says V8 or V4. You may not feel anything, but if you watch your tach, it may fluctuate about 100 to 200 rpm. Put the gear select handle to manual and that will stop and the transmission locks the engine in V8 mode. The range device does the same, only you can keep the selector in full auto mode and not mess with using the paddles. Excellent insurance IMO to prevent torque converter problems down the road.

Like you, I bought my 2016 C7 A8 used, with 4K mi’s. Have had no problems, but did see the RPM flux. Installed the range device at 4500 mi’s and been extremely happy with it. Stays plugged in full time with no issues. It has the latest factory updates. Good advice to buy factory direct! In the future, I will not buy or drive a new C7 A8 without the device.

plake

I just ordered the Range device, still available with the $10 off promotion. In the big picture money well spent if it prevents damage and issues in the future. Latest software makes it easy, just plug it in and forget it. I did read on here that guys were getting another cord with switch so they could turn the unit off to prevent battery run down. I mentioned that to Range yesterday and they said that isn't necessary with newest version and they also mentioned that was not a good idea anyway, needs to be plugged in directly. Maybe the reason for some of the CEL, etc. issues.

pnsnkr

This thread has details on the Driver Information Center (DIC) [I didn't invent this acronym]

Stingray DIC Menu Hierarchy

The Fuel Range/Instant Fuel Econ menu will show if the AFM is in V8 or V4 mode

Flo

Just had today the fluid changed.
My dealership said it will normally fix the issue which was light. To see.

plake

mountainears

I leave mine in ALL THE TIME, have not seen any issues (using 8.6).

Now I never saw issues before, but prior to 8.6 I couldn't use it much because it threw codes.

I purposely left it in for a couple weeks and didn't drive the car, did not sense any issues. Normally though if I leave the car for any long period of time I have the battery tender plugged in anyway, so even if there was an issue I wouldn't worry about it.

Personally I say give it a shot....see for yourself.

Dif

To add to my post # 632, I just got back from the Dealer where I went to have them check mine out possibly to do the Trans Flush.
Went for a 20 mile ride with the Tech and I talked extensively with him about what I thought as he was driving.
Told him I do know there's is a light shudder "sometimes" as I already mentioned in my previous post.
He told me he's done quite a few flushes in the C7's, and after we returned to the Dealer he felt there was Not a problem.
The Dealer is 20 miles away and I put on another 60 miles taking a long way home.
Now, today being 90 degrees out the the trans worked great when in V4, and this is the norm in warm/hot weather.

To sum things up, should I have had them do the Flush anyway to see if there was any difference after wards ?
Maybe.
But there's one thing he asked me that made me agree with his opinion that it didn't need the Flush, especially since he has done quite a few and knows the difference.
He asked if I would get a Noticeable shudder when in V4 going up a slight incline when "lightly" increasing the throttle.
And it does Not do that, and never has in the 15,000 miles I've put on the car because it instantly goes into V8 with the slightest throttle increase.
So we agreed to leave well enough alone for now and he said they've documented this Service check.
And with 3 1/2 years left on my extended warranty, if at anytime I feel I need the Flush to let them know, and they'll do it no problem.

Info for what it's worth if it helps anyone