dckotwicki

I own a 2016 Z06 with 3500 miles on it. Recently went into northern Michigan for a weekend get away. The roads are smoother and quieter with less traffic noise. Some roads have rumble strips imbedded into the side and center of the road to get your attention when you wander left or right. During the drive, I began to notice a similar but quieter noise. I began to study the road surface but could find nothing to connect to this noise. I started to look elsewhere for the source and discovered a direct correlation to the AFM (active fuel management / 4 to 8 cylinder modes).

With the cruise control on and on a relatively flat road I began to notice this subtle rumble noise (similar to hitting rumble strips but much quieter) occurring when the engine was in 4 cylinder mode. When it went back to 8 cylinder mode, the noise went away. The noise always happened before returning to 8 cylinder mode. The duration of the noise ranged from 1-2 seconds to several seconds (5-10 seconds) and always disappears once the engine is back to 8 cylinders.

I am not a mechanic and do not know the mechanism that causes the engine AFM to activate, but I wonder if there is something acting up in the system that activates the AFM.

Anyone experience anything like this or have any possible explanation for what is happening?

The engine had the 500 mile oil change at the dealer and again at 1000 miles. Both with Mobil One. Oil level is where it should be and shows 65% oil life.

My eternal fear on a car like this is a "No problem found" response from the dealership.

Mr. Jones

The noise you describe sounds normal
in V4 mode.

dckotwicki

Could you be more specific and describe whats going on internally to make this noise?
This noise is not constant in V4 mode, it only happens before going back to V8 mode.
I've had 2 C7's (this is my 2nd) and never noticed this before.
May not be, but it makes me wonder about oil starvation somewhere.

Fast6.3

Its just the exhaust kind of sounds like a vibration but its normal thats why gm put the extra afm valves in the exhaust

cam30era

There are a couple of threads in the General section that might be germane:

https://www.corvetteforum.com/forums...asionally.html

https://www.corvetteforum.com/forums...here-i-go.html

https://www.corvetteforum.com/forums...th-anyone.html

Oskee

Remember your Z06 does not have the AFM valves before the mufflers only the NPP after the mufflers. Also you did not mention if you have a A8 or M7. If you have the A8 drive it in manual mode which will keep the AFM off and see if it still makes the noise. What I believe you are hearing is the change in exhaust tone . My Z06 also makes the noise very faintly. which is normal and thats why I drive mine mostly in manual mode (paddle shift)....

dckotwicki

It is an A8.
When the noise occurs and I place the vehicle in manual mode the engine goes from V4 to V8 the noise goes away. All the time. This noise occurs while in V4 mode and always is followed by the change to V8 mode. Length of this noise vary's from 1-2 seconds to 5-10 seconds. It does not during the entire time the engine is in V4 mode, only near the end before going into V8 mode.

Description: Imagine driving slightly off the road and hitting those rumble strips that are sometimes on the outside of your lane. It is that kind of noise, but only / maybe 10% as loud. It is as if the engine wants to go back into V8 mode but can't quite get it done... then finally goes into V8 mode and the sound goes away.

This is not an exhaust system noise. To me it is an engine noise.

sTz

I posted in your other related thread: https://www.corvetteforum.com/forums...le-strips.html

BOBSZ06

Duplicate question:

https://www.corvetteforum.com/forums...post1593133675


Belt tensioner replacement video:

https://www.corvetteforum.com/forums...post1593134039

davanz

I was at the NCM Bash in the Spring of 2009 or 2010 and Tadge was fielding questions from the audience in the theater. One question that he addressed was along the line of "why does the LS3 engine not have cylinder deactivation, (AFM)". At that time he explained that the engineers had looked into it and had performed some experiments. He related that a problem that was being worked on at the time was that when the engine went to V4 mode there were vibration/harmonics issues in the drivetrain between the engine and transaxle. Therefore, at that time a system we now know of as AFM was not developed and put into production cars with rear transaxles, (Corvettes).
Evidently the engineers found a way around this issue with the LT1 but could there be some lingering problems under certain RPM/throttle position/load conditions that have not been fully erased?

subfloor@centurytrans

You have to listen fairly carefully with the sound turned up, but in all three videos the growling sound it makes right before switching back to V8 mode is definitely noticeable. Please let me know if this is the same thing that other people have been experiencing.

Grand-C7

Next time around check to see if your RPMs are stable when this happens. This could also be a Toque converter issue.