NPP Valves - Only One Open When Engine Off
Thread Starter
Advanced
Joined: Sep 2004
Posts: 81
Likes: 16
From: Phoenix Arizona
NPP Valves - Only One Open When Engine Off
I have a 2019 Z06 that I just purchased. When the engine is off, the left side valve is closed in the exhaust pipe and the right side is open. There are no codes in the system. Is this normal operation?
Safety Car
Joined: Dec 2012
Posts: 3,859
Likes: 1,865
From: St. Louis Metro East IL
NO, the valves spring open when the car is off or power removed. The valves take voltage to close, spring should open when no voltage.
Sounds like a dealer visit for a new actuator.
NPP valves don't set codes.
Ron
Sounds like a dealer visit for a new actuator.
NPP valves don't set codes.
Ron
Last edited by RonC7; Dec 29, 2020 at 07:47 PM.
Thread Starter
Advanced
Joined: Sep 2004
Posts: 81
Likes: 16
From: Phoenix Arizona
Thanks for the reply. The actuators are working fine when the car is running and I had an extra actuator that I swapped out and it did the same thing. As for codes, my car is a 2019 Z06 and it definitely set codes for the NPP actuators. The reason I know this is because when I bought the car, it had a Corsa cat back exhaust system on it without NPP. There were codes for the actuators because they were not hooked up when I checked it with my scan tool. I sold the Corsa system and replaced it with the OEM exhaust.
Safety Car
Joined: Dec 2012
Posts: 3,859
Likes: 1,865
From: St. Louis Metro East IL
Well, the power switches to both actuators at the same time and only one opens when cold. But both work when the car is running. So - the spring is there.
Sounds like the valve or actuator is sticking or binding under certain conditions or temps.
If you remove the actuator, does the valve flapper move freely?
Certainly sounds like a mechanical issue with the one valve.
GL
Ron
Sounds like the valve or actuator is sticking or binding under certain conditions or temps.
If you remove the actuator, does the valve flapper move freely?
Certainly sounds like a mechanical issue with the one valve.
GL
Ron
Heel & Toe
Joined: Jul 2020
Posts: 15
Likes: 2
Realize this is an old thread but did anyone ever figure out why it was happening?
I just put NPP on my car with an Akrapovic controller and if I shut down with the valves closed, only the driver side opens when shut off. The passenger side stays closed…but appears to eventually make its way open. Another time I heard some grinding even after I unplugged the power source and it didn’t open. If I push against the closed valve, it will open. I cycled it through all modes with the engine off and it opened or closed both valves as it should.
I just put NPP on my car with an Akrapovic controller and if I shut down with the valves closed, only the driver side opens when shut off. The passenger side stays closed…but appears to eventually make its way open. Another time I heard some grinding even after I unplugged the power source and it didn’t open. If I push against the closed valve, it will open. I cycled it through all modes with the engine off and it opened or closed both valves as it should.
Heel & Toe
Joined: Jul 2020
Posts: 15
Likes: 2
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Heel & Toe
Joined: Jul 2020
Posts: 15
Likes: 2
It does not look like it’s rubbing but clearly something is sticking somewhere. It does have more carbon on it than the other valve does. I’ll try the cleaner on both and see if it goes away. If not, I can swap actuators and see if it follows the actuator.