NPP Exhaust Valve Flutter
Thread Starter
Cruising
Joined: Feb 2024
Posts: 10
Likes: 3
From: Houston/Atlanta
NPP Exhaust Valve Flutter
I've noticed that whenever I rev my car I get this weird flap on the decel from the npp valves before the muffler. It's for sure those valves because when I pull the fuse my exhaust sounds amazing crackle and popping. I replaced them before because of a broken lifter spring that actually cause my intake manifold to melt and sent so much heat back it blew my cat on side. I know some have said they must be reprogrammed but they still open and close fine. Worst case Ive seen a post about using hp tuners to tune out everything that triggers the CEL (its actaully a couple of codes that come up from pulling the fuse). Like to know what some of you guys think about my situation.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
I've noticed that whenever I rev my car I get this weird flap on the decel from the npp valves before the muffler. It's for sure those valves because when I pull the fuse my exhaust sounds amazing crackle and popping. I replaced them before because of a broken lifter spring that actually cause my intake manifold to melt and sent so much heat back it blew my cat on side. I know some have said they must be reprogrammed but they still open and close fine. Worst case Ive seen a post about using hp tuners to tune out everything that triggers the CEL (its actaully a couple of codes that come up from pulling the fuse). Like to know what some of you guys think about my situation.
Bill
Thread Starter
Cruising
Joined: Feb 2024
Posts: 10
Likes: 3
From: Houston/Atlanta
Yes I've actually seen a set of them floating around offer up for about $300. I was going to buy them but I didn't know what to do with the plugs and wires. I've been wanting to buy hp tuners for a while now only reason I haven't is that I have mac computers. Guess I'll bite the bullet on a new laptop solely for tuning. Thank you for the advice that clipping the actuator somewhere and forgetting it tip did peak my interest but theres no little space up there.
Drifting
Joined: Jun 2013
Posts: 1,428
Likes: 478
From: Maryland, USA
is it the rattle issue from the passenger side npp valve?
I have it on my list to fix, since I notice this is happening on mine especially after high flowing exhaust now.
https://www.corvetteforum.com/forums...-1500-rpm.html
I have it on my list to fix, since I notice this is happening on mine especially after high flowing exhaust now.
https://www.corvetteforum.com/forums...-1500-rpm.html
Thread Starter
Cruising
Joined: Feb 2024
Posts: 10
Likes: 3
From: Houston/Atlanta
If mine sounded that good I could possible live with the noise lol. I have a video on my phone I'll upload to youtube and put on here tonight. I will say that ive heard it on a lot of c7's. For now heres a car that makes the same sound. The sound I'm talking about is at the 1:08 mark on the video. It sounds like the exhaust is flowing then catches on something creating two different sounds on the decel.
