Curious about this since the previous generation had issues and theres a class action on the issue. If the C8 Does, did GM do any revisions to the AFM design/parts for the 8th Gen?

 

Yes, at cruising, the engine goes to V4. Some complain about a noise it makes when it does that. I have never heard it. I think the feature is great. A road trip showed us getting over 27 mpg due to this feature.

 

Yep I never used V4 in my two C7 M7s as with a standard shift there was some modest jerkiness on switching. In addition seldom use the Interstate so never in 7th gear. Never found a use for 6th where I drive!

With the DCT it's seamless. Can't tell it's going in or out. Howver much of my driving is in Z Mode power set to track. It only goes into 6th gear at ~72 mph, and where I drive mostly stays in 5th (never in 7th or 8th and will not go into V4.)

All those gears and V4 help GM get the best mpg possible in the EPA defined test, which probably uses less than 50 hp max. In fact, 4th, 5th, 6th, 7th and 8th are all overdrive ratios!
4th = 0.88:1
5th = 0.66:1
6th = 0.51:1
7th = 0.40:1
8th = 0.33:1

The other Mode I use in MY Mode set to Sport where it uses all 8 gears and V4. BUT mpg is more dependent on your right foot in all but highway driving! For fun with high gas prices I ran for one tank full in Z Mode and another with MY Mode. Tried to drive about the same in both but probably somewhat less right foot when in MY Mode. Got ~2 mpg better in MY Mode where I typically get ~18/20 mpg in mixed mode in my rural driving (I keep a spreadsheet.) Not a lot of stop and go until I hit town ~25 miles away but a lot of stop, turn and accelerate! BUT in MY Mode the transition to V4 and back is seamless.

PS: Have not seen many issues with lifters etc. Bet the only folks making money in any class action lawsuit are the attorneys!

 

just got 29.9 mpg on a recent 650 mile trip with the 4 cyl mode showing up about 90% of the time. Average speed was about 10pm over the posted limit. This made me very happy.

 

Are people using the range device w/ their C8s like they do for the C7s? Or is it a non-issue?

 

^^^
From someone who never had my two C7 M7 standard shifts in V4 because I never drove in ECO. It was slighlty jerkey going in and out with a standard shift, in the C8 it's seamless!

Be foolish to mess with one if it were available- don't think any manufacturer would be foolish enough to build! . All you have to do is drive in Z Mode power set to track and use a light right foot. It will never go into V4, can't! If you want to use more than 5th gear (after 72 mph it will go into 6th) just use the upshift paddle!

 

Keep the DCT in manual mode all the time as God intended and you won't have to worry about AFM

 

Issues? Class action lawsuit? Links?

Never had an issue with it with my 2014 C7. No issues with my C8 either. Heck, if I could lock it into V4 mode for city driving, I probably would!

 

I had the lifters replaced at 3,000 mile in my '19 C7 A8 Z06 thanks to AFM. Got a Range AFM disabler after that.

 

Exactly what part of the AFM caused the lifters to fail? A Corvette tech that participates in this forum said he has replaced about an equal amount of non-AFM and AFM lifters in C7 engines, and that the lifter failure rate isn't abnormally high.

 

I have a 2023 C8 and the auto shifting from 8 to 4 cylinders is flawless and seamless. If I don’t look at my monitor I wouldn’t even realize I was during in 4 cylinder mode.

 

A range device isn't available for the C8

 

^ This is the case.

 

I drove from Fort Myers to Key Largo and back again in Sport Mode and got 31.1 mpg.

 

GM has had an issue with AFM and lifter failure for years, especially in some of their trucks. I did quite a bit of research on it after I had the failure. I have a good friend who had to have the engine in his Chevrolet pickup truck replaced because of lifter failure. It was attributed to AFM. MOPAR has also had an issue with vehicles equipped with AFM. Lifters shouldn't fail at 3,000 miles on a car that was never tracked and was well maintained. I didn't notice any performance difference after I installed the Range disabler, but my car did seem more responsive.

 

Yes, but it is a rare occurrence for Corvette LT1/LT4 engines, and I haven't seen any LT2 lifter failures attributed to AFM system failure. Just because a lifter failed doesn't mean it is related to AFM.
The AFM lifter failures in GM trucks are generally attributed to oil pressure/contamination and AFM passages being blocked. Perhaps because trucks get less frequent maintenance or perhaps the AFM design is different in trucks, we don't know.

At any rate, there is no evidence that not using AFM in LT engines prevents an AFM failure that would have otherwise occurred. See Post #27 of this thread:
https://www.corvetteforum.com/forums...-common-2.html

 

https://www.mylemon.com/lemon-law-blog/general-motors-engine-valve-lifter-class-action-lawsuit/#:~:text=The%20class%2Daction%20lawsuit% 2C%20filed,be%20damaged%2C%20necessitati ng%20an%20expensive

https://www.classaction.org/gm-lifter-problems-lawsuit

 

^^^
Like I said, a few people have an issue and the internet thinks the sky is falling. With more than 100,000 C7s on the road, if AFM failures were a common problem the C7 forum here, and on other sites, would be filled with complaints. The reality is that C8 DCT failures are more common, and complained about more, than lifter failures on C7s.

 

what does this have to do with the C8?

 

Unfortunately The C8 has AFM (v4) mode. Yes it is mostly not noticeable, but you will feel it and hear it if you have a sensitive butt meter and are highly aware of what you C8 is doing mile after mile. I will be the first in line to tune the feature out when it can be done.