I'm a newbie to the C8's, but an oldie with the C7's. Can I take the AFM out of my C7 and plug it into a C8??

 

I'm assuming that you mean you want to move your AFM disabler from your C7 to your C8 and have it work. The answer is likely no unless you purchased the Carbyte disabler and then it only works on pre 2024 C8s.

 

The post above answers your question. But...do you have your C8 yet? The transition to the V4 mode is very subtle, and many owners report not noticing it at all. I can detect it, but it is very subtle. You may find you do not need to obtain an AFM disabler. Even though I can tell, I don't have one and do not intend to get one.

 

Hmmm? Interesting. Don't have the car yet...ordering it tomorrow since I can't seem to find one set up the way I want.

 

While I dont notice the power transition, that is very smooth, I certainly notice the AFM valves clunking and there is a bit of a hard shift at the same time into 3rd on decel while in v4 mode. This happens in slow stop and go traffic. Its livable, but slightly annoying.

 

That's right. Mine had some noise when the valves moved but that stopped. I've never had any change in shift smoothness that I have noticed. But, I'm not saying others have no reason to disable AFM. I was just saying that one may wish to try it out before getting that. I have read here that the C7 was much more noticeable than the C8 - so some that needed to disable it on the C7 may find its unnecessary on the C8.

 

On my 21, anytime I lift off of the accelerator, it goes into V8 mode.

 

C7 AFM was a little more noticeable for some people (my 2015 manual was barely perceptible, but I've had friends say there's was more noticeable). The C8 is virtually undetectable unless you see the indicator on the dash in stock form (if you have an aftermarket exhaust, the switch can become a little more noticeable). As mentioned above, the Carbyte is the only one that works on the C8, and that's only 2024 and earlier for now. Also, FYI, AFM is enabled in 4th gear and above in MyMode, Weather and Tour. It's enabled in 5th and above in Sport. It's disabled in Track and Z-Mode if power/trans is set to Track, or when using Manual mode.

This is how both my 23 Stingray and 25 E-Ray behave with V4.

 

No won't work. Carbyte will work but only up to 2023. 2024+ are SOL for the time being.

 

…you sure you’re not referring to the NPP valves…I don’t think I’ve ever seen my C8 go into V4 mode in stop and go traffic…

 

I don't know about stop and go traffic - that can vary a lot. But I do know that on back roads with even short stretches of straight, flat road it will go into V4 very quickly, and come out just as quickly going uphill, or coasting down hill. I can detect this, but its not especially noisy or clunky, and I don't have the rough shift associated with it. I don't know if its relevant to the discussion or or not, but description in the manual for Cylinder Deactivation says there is some "hysteresis" and the AFM valves (in the muffler now) may remain closed even after the car has exited V4 mode, until a certain amount of engine torque is demanded. So I think that means that if the car was in V4 mode, and then started to coast down hill with no throttle, the car will exit V4 mode, but the AFM valves might stay closed until some throttle is used. So if the AFM valves are noisy, that noise when it moves may be heard later when they open.

 

Positive, its the AFM valves that clunk, not loud, just with no radio on and windows up I can hear them (along with the DI pump tick). Mine will engage V4 mode in city traffic everyday.

 

AFM is a pain in the ****. Most owners can't stand it, some say they never hear it, which is hard to believe.

I had mine along with cold start permanently removed on my 12/2023 E85 tune. Happy it's gone and have never remotely missed it.

Good luck and Happy C8 motoring.

 

I despise AFM. I bought the Carbyte adapter. It works fine in the meantime. Meantime meaning when GM stops extorting people for thousands of dollars to turn it off in the ECM.

 

I never hear when my AFM switches - if it wasn't for the light I would never know. Maybe it's because mine is a HTC, maybe it's my Borla S-type exhaust which always sounds sweet.

 

If you want to disable afm valves you could just disconnect the wiring harness and add some valve simulators.

Afm valves close when the car goes into 4 cylinder mode. 4 cylinder mode is only activated when the car is at a relatively constant speed with a specific amount of throttle applied over a few seconds. It needs at least a little throttle input, at a constant application, to engage 4 cylinder mode. When you get off the gas the car immediately goes back to v8 mode or when you give it more gas.

 

I'd love to have one but there isn't any compatible for my 25.

 

If you're not a DIY'er, that's got to be an expensive dealer job?

 

True that. It won't prevent the car from going into V4 mode. It would appear that when V4 is active both the Cylinder Deactivation Exhaust Flow Control Valves (aka AFM valves), and (if you have the NPP muggler) the Tailpipe Exhaust Flow Control Valves are commanded shut. So in some cases, even with the AFM valve action circumvented, the operator may still hear a noise associated with the tailpipe exhaust flow control valves moving, with the NPP option.

Details: The Service Manual describes the exhaust flow control system as having two subsystems:
"1. The exhaust tail pipe flow control valve system.
2. The cylinder deactivation exhaust flow control valve system. Also known as the active fuel management (AFM) exhaust flow valve control system."

When AFM is active it closes the AFM valves. But it also says that when AFM is active, it takes control of the exhaust tailpipe flow control valve system and commands those valves shut as well. When it exits V4 mode, it will return control to the engine sound setting for the selected mode. LIke this:"When active fuel management is operating, the exhaust tailpipe flow control valves are commanded shut resulting in a quieter exhaust note until the active fuel management system deactivates with increased throttle demand at which time the exhaust tailpipe flow control returns to the operational status determined by the vehicle specific mode that is being used." So (if the Service Manual description is accurate) when operating in Sport or Track Driver Mode, or in Z-mode or MyMode with engine sound set to Sport or Track, the tailpipe exhaust flow control valves will be open under most all driving conditions so they will close when going into to V4 mode.

I don't hear my valves move any more on my 2021, although when it was newer I did hear them sometimes. I can tell when the car is in V4 mode - to me I can sense or feel a difference in the powertrain sound. I find it to be subtle, and I am not surprised that many don't hear, or if they do, are not concerned about it. The only time I don't like it is on back road leisurely cruising where it will transition in and out of V4 mode frequently. But in that scenario I don't like the automatic gear selection in any of the engine/shift settings, so use Manual Shift Mode and that prevents the V4 mode.

 

yall talking about 2 different things. The Op is talking about preventing the car from going into V4 mode; the latter posts are talking about the valves in the exhaust. The carbyte works on my 2020. It is aggravating to have to link it to my phone every time I drive to make it work, though. The range finder was a much better option, but it's not available.