Stan0324

I have set the engine sound management set to Sport and everything has worked fine until tonight. I started the car and heard a pop coming form the right side of the exhaust. At this point, the exhaust became quieter. Drove for a few miles and it stayed the same. Turned off the car to see if anything would reset and it remained the same. Went back into sound management and changed the settings. There was a difference going from tour to sport but not like it was before.

It appears that something within the NPP is not working properly. With only 1900 miles, I am still under warranty but just wanted to know if anyone else has experienced this problem and if so what was the fix. For reference, it a 2015 Z51 A8.

benapm1

Had something similar happen on C6. Pulled fuse and put it back in and it was fixed. c7 may be different

grandpawmoses

If the other recommendation doesn't work, try to look at the NPP motor back at the butterfly valve for a problem like a broken or disconnected linkage. That's a very costly part & if it's bad, go to see Mr Goodwrench.

Stan0324

Going to pull the fuse to see if the sound comes back. If it doesn't then it must be in the linkage. Might be a trip to the dealer.

Thanks for the info.

pmirp1

Stan I have the same problem, with only 170 miles on a 2016 Corvette Stingray non z51 automatic. It happened at 160 miles. I think I heard a pop and then the engine didn't sound the same, even in sport mode. Even though there is some change in noise when I go from sport to touring and back. I have the performance exhaust. Did you find a resolution to your problem? I took to dealer on Friday (two days ago) they said no problem after looking at for a day. I am taking it to service manager on Monday for him to look at. Really appreciate any help you may be able to provide.

Larry/car

I am afraid as the miles accumulate on our fleet more problems with the NPP system will develope. The exhaust valves reside in a harsh environment (hot/cold, exhaust residue and road dirt) and will need maintenance/replacement over time.

sTz

^^^ This.

JerryU

Had no problems with NPP in my 6 year old C6 and none (so far) with my September 2013 built C7.

Dif

Sounds like one of the exhaust flaps is stuck closed.
Look inside the exhaust tips at the flaps.
Then have someone change the exhaust back and forth from Tour to Sport.
See if both flaps are opening and closing like they should.

Foosh

I don't recall that being a problem with the C6 Z06, which had a similar system. Many other makes use similar valved exhaust systems w/o widespread issues as the cars age. My Jaguar F-Type had it as well.

The parts that make the system work are shielded. Brake systems are exposed to the same harsh elements.

Skidplate

Also take a look at the AFM valves (further upstream). Perhaps one of those went wonky. They will definitely affect the sound.

Old Yellow

The C6 had a totally different form of operation. Vacuum (C6) vs Electronic actuators (C7). In the harsh environment electronic actuators are more likely to fail, and are proving to do so.

On the C6 all electronic components were inside the car itself. With the C7 all failures are occurring at the electric actuators: whether it be AFM, or NPP actuators.

Ed

Foosh

The wheel speed sensors for ABS are electronic and located near the brake discs. They have been on most every car for many decades now.

Old Yellow

That is a hall effect magnetic sensor, we are talking about an electric motor, and integrated circuitry contained within the motor housing; attached directly to the exhaust pipe.

Apples to watermelons.

Ed

Foosh

The point is you don't know whether they are failing because of exposure to "harsh elements" or are just bad parts. Moreover, I don't hear of very many failing at all.

Like most things on this forum, it's all just pure speculation without foundation. Seems to me the majority of Corvettes are garage queens, only very rarely exposed to harsh elements.

Old Yellow

Read further. There are a lot of failures on cars that are used as advertised, and bragged about by the chief E. Chevy even eliminated the AFM valves on the Z06. If you don't put on the miles the probability of failure drops way down, but these lower use cars are the ones that are experiencing squeaks when the valves open or close.

the only harsh element affecting them is the heat. Search the posts, and you will find pictures of the plastic cover on the actuators are melting, and coking. It's not speculation at all.

There is a feedback signal from the AFM actuators that will turn on the CEL in the event of a failure. A AFM valve failure can cause engine damage, and at the very least an extreme loss of power if the valve remains closed when the engine reverts back to V8 mode. The feedback signal is not used on the NPP actuators even though the same part is used at both locations.

I don't have the answer, but the actuators are failing due to heat, and isolation from the heat is what will cure the problem.

I originally responded to your post, because you seemed to not understand why C6s worked flawlessly, But C7s are not. I answered that question with an explanation of the functional difference between the two systems.

Beyond that point I will not argue with you that they should not fail if properly designed.

Ed

Larry/car

Seems people who are purchasing the C7 Corvette are driving more and racking up more miles in all kinds of weather. It will be interesting how the NPP actuators hold up.

Foosh

Thanks Ed,

Your clarification that it's a heat problem w/ the AFM valves on cars run hard does make sense.

I thought we were talking about the NPP valves and exposure to moisture and environmental conditions, but we clearly agree that what issues do exist w/ heat represent a design flaw. The elimination of the AFM valves in the Z06 is tangible evidence of that.

Henna Chevrolet

and its not just the GM parts failing either, I have one in the shop now with a Flowmaster system and their parts are failing as well. its a complex system, made worse with adding aftermarket parts. After spending hours looking on line for the aftermarket valves, we found the factory ones will bolt up to the flowmaster mounts(customer was not interested in putting it back to factory, due to cost) after installing the GM valve on the passengers side, the drivers failed on the road test. now the tech has to take it all apart again to mount the drivers side. I'll grab the aftermarket ones and take the cover off to see if I can locate the failure.
this does not seem to be a wide spread issue here in Austin, but I have heard of one ZO6 that I will be road testing with the owner soon. I'll have him toggle the driving mode switch and look for changes in the valves, as recommended earlier in the thread.

Internets_Ninja

Just an an FYI, the AFM and NPP motors are sensitive to over tightening. They have a very low ft lb torque value with lock tight applied. Even a couple of pounds over tightened will cause all sorts of issues. Make sure your techs are being gentle with them.