Odd noise when going from V8 to V4
01-22-2017, 10:18 AM
#1
Drifting
Thread Starter
Odd noise when going from V8 to V4
Probably "normal" but does anyone else have this?
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
01-22-2017, 10:23 AM
#2
Mine sounds like a 'mechanical' linkage shifting noise. I first thought it was the gearbox (A8) but it happens just before the v8 icon changes to v4. Mostly in the lower gears and and slower speeds. Driving me nuts, the dealer will run some tests when the weather warms up. Apparently they cannot run the diagnostic in cold ambient temperatures (???).
01-22-2017, 10:26 AM
#3
E-Ray, 3LZ, ZER, LIFT
Member Since: Sep 2007
Location: NE South Carolina
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Probably "normal" but does anyone else have this?
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
Frankly I have an M7 and seldom have used ECO Mode in 3 years so it doesn't go into 4 cylinder mode and don't hear it! Also there is so much tire and road noise in the C7 I have the sound system playing my SD card songs in shuffle mode as soon as the car starts. It's never off! Drowns out a lot of sounds.
Last edited by JerryU; 01-22-2017 at 10:28 AM.
01-22-2017, 10:34 AM
#4
E-Ray, 3LZ, ZER, LIFT
Member Since: Sep 2007
Location: NE South Carolina
Posts: 29,571
Received 9,646 Likes
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Mine sounds like a 'mechanical' linkage shifting noise. I first thought it was the gearbox (A8) but it happens just before the v8 icon changes to v4. Mostly in the lower gears and and slower speeds. Driving me nuts, the dealer will run some tests when the weather warms up. Apparently they cannot run the diagnostic in cold ambient temperatures (???).
Note those valves are in all C7s and not related to the NPP valves-they are before the mufflers. Might spray with WD-40 as a quaick check to see it it is reduced, although WD-40 won't last. Need a higher temp lub, perhaps like the Moly brake pad lub.
Last edited by JerryU; 01-22-2017 at 10:37 AM.
01-22-2017, 10:34 AM
#5
Racer
Member Since: Feb 2005
Location: Southeast - Alabama, Georgia, & Tennessee
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3 Posts
Probably "normal" but does anyone else have this?
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
01-22-2017, 10:59 AM
#6
Drifting
Thread Starter
Mine sounds like a 'mechanical' linkage shifting noise. I first thought it was the gearbox (A8) but it happens just before the v8 icon changes to v4. Mostly in the lower gears and and slower speeds. Driving me nuts, the dealer will run some tests when the weather warms up. Apparently they cannot run the diagnostic in cold ambient temperatures (???).
01-22-2017, 11:34 AM
#7
Safety Car
I actually need to see the indicator change to pick up the 8/4 change on my C7. But I wonder if the fact I have a convertible is a factor. The vert might be more isolated from rear-end noise than the coupe.
01-22-2017, 12:29 PM
#8
Le Mans Master
Mine makes a similar sound and I can feel a mild clank while it does it.
01-22-2017, 02:35 PM
#10
Probably "normal" but does anyone else have this?
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
When going from v8 to v4 I can hear a slight noise. It doesn't do it all the time (or at least I can't hear it all the time). Its not a bad noise, its not a shudder, not a click/clack or a thunk, and I only hear it when it goes from v8 to v4, not v4 to v8.
Best I can describe it, say the word "Chair" it would be the "Ch" sound.
Next time you drive listen for it, turn off radio, and turn down HVAC blower.
Switching from V8 to V4 . I can duplicate it by steady state driving at speeds below about 50 mph by pulling the shift selector into M causing V8 mode then placing shift selector back into D. As the car goes into V4 mode, as seen on the DIC, I hear the "CH" or "CHUFF " sound. The only valves moving at that point are the AFM related valves that close when you go into V4 mode. Our SM found a service bulletin that deals with noisy valves and requires a special lube that they used on mine.The lube is more for those who were getting a squeak on valve movement and my problem is not a squeak.
After I got the car back I still had the noise. They lifted the car in the service bay, hooked up the computer to it and the mechanic was able to command the AFM valves ( just before the muffler) open and closed.....no noise BUT the engine was not running.
I have two thoughts on the momentary "CH" sound...
1) With the engine running in V8 mode the AFM related exhaust valves are open. I am beginning to think that when you go into V4 mode and the AFM valves close they do so AGAINST exhaust flow and that may be a momentary pneumatic flow change sound we are hearing.
2) I have noticed that when you go from V8 to V4 there is a very small momentary "blip" on engine RPM on my car.....so, am I hearing a momentary induction noise?? If I'm in 4th or 5th gear, V4 mode and I give the accelerator pedal a small but quick shot, not enough, to bring it out of V4, I hear the exact same noise.....probably induction air noise.
IF ANYONE GETS A SOLID ANSWER TO THIS NOISE PLEASE POST,PLEASE..........tks