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NPP Exhaust Issue...Or Non-Issue

55K views 196 replies 48 participants last post by  AndyT 
#1 ·
Have the NPP programmed for continuous open, however, when going through the gears (A6, S or Tr)) it closes in 3rd gear, until I give it a little gas, then it will open and stay open through the rest of the gears. Anyone else experience that? Is there a fix? Thanks.
 
#3 ·
How do you know your NPP is closing when you go into 3rd? Even with the NPP set to be 'always open' you will only hear a difference (that is, significant increase in its loudness) when you are accelerating/stepping on the gas. Otherwise even with it open, it will settle down into a relatively quite mode, such as when you are cruising at highway speeds until you step on the gas.
 
#7 ·
I believe there appears to be some confusion in this thread: with the NPP you have one of two settings as options in personalizing your preferences on your Stingray. You can have NPP set to "Auto" which means that the valves are controlled by (linked to) the Mode you have selected, ie: eco, tour, sport, track and each in turn controls the valves differently resulting in a audible difference between relatively quiet and authoritatively loud in combination of your current throttle position but dependent on the drive Mode. Or you can have NPP set to "Auto Off," which means the valves are set to be open at all times, resulting in an audible difference between relatively quiet and authoritatively loud solely dependent on your current throttle position independent (or regardless) of your drive Mode setting. I seriously doubt you can 'feel' the valves open or close but you can definitely hear the difference, and of course, if you are behind a Stingray at exhaust eye level, you can actually see the valves open or close.
 
#8 ·
When I slowly progress through the gears starting with first, the exhaust is open, when it hits third, I hear a phoomp, gets totally quiet, while still keeping the same foot pressure, in about two to three seconds it opens back up as before. Is it something to be concerned about or just put up with it. Heavy pedal, no issues, just light pressure on the pedal.
 
#9 ·
Norm someone with a manual will have to try duplicating your experience. Mine is an auto.
 
#12 ·
There also seems to be an rpm threshold where if you are below around 1400 is switched to a quieter mode, no doubt due to a droning effect if fully open. What rpm to you hit when you first shift into third?
 
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#15 ·
There also seems to be an rpm threshold where if you are below around 1400 is switched to a quieter mode, no doubt due to a droning effect if fully open. What rpm to you hit when you first shift into third?
Right around 1400. When I keep more pressure on the pedal (naturally goes faster) I don't hear it closing, keeps a constant drone. This closing only happens when I'm proceeding through the gears (A6) using just the slightest foot pressure (like taking off slow) and proceeding slow through the gears.

I went into the DIC and observed the ACM moving from V4 to V8 and back but did not find a source to disable the V4 mode.......do-able???? Thanks.
 
#23 ·
Just talked to the GM certified techs at Carlisle, they said that pulling the fuse would not hurt anything. The exhaust closes to keep the federal government noise requirements in check at idle and cruising speed.
 
#25 ·
Pulled #41 today, drove around a while, no codes. Got a little bit more of a growl and seems like it stays open more than not now, however, at light touch acceleration, still feels like it's hesitating, and the exhaust sounds like it's fluttering a bit.
 
#26 ·
Is it an A6? I wonder if AFM is cutting in...
 
#28 ·
Well as it turns out pulling up the rear carpet to expose the fuse block is very difficult and I think I broke some clips. However I did find out that if you remove fuse 41 although on the legend it says its a spare it disabled the remote start. It did not change the exhaust note when I started it from inside the car. That does lead me to believe the legend might be wrong and those fuses do have an impact on what happens with the car.
 
#29 ·
So as a further update I removed all the fuses 39 to 44 and Guess what the remote start worked again but no change to the exhaust sound. Maybe it's because I don't have the NPP option. But it still seems weird to me that a spare fuse would disable the remote start. Aloha, Mark
 
#31 ·
Yeah, Mark, you have to have the NPP before pulling a fuse will make a change to your exhaust note. Without NPP there are no extra set of valves hooked up to the circuit driven by that fuse.
 
#32 ·
OK I tried out all different combinations but ultimately realized they are really replacement fuses slot 39 is a 30 amp, 40 is a 25amp, 41 is a 20 amp, 42 is a 15 amp, 43 is a 10 amp and 44 is a 5 amp. That's it. I'm sorry I was hoping to figure this out but that's all there is. Aloha, Mark
P.S. I don't understand why pulling out a spare fuse would disable the remote start?
 
#35 ·
Also I saw a thread about dislikes for the C7 and have to agree with 2 of them. First the cup holders suck, if you go forward or back or right to left you're drinks going to get all over the car. The second has to do with the Z51 option for the Chrome Aluminum wheels, I love that they are 19 and 20 but why is only 2" Chrome on the outside and not the entire wheel? Other than that I love this car. And since we have all said we have owned multiple Corvettes I would have to say I would rather own this car than a La Ferrari. Aloha, Mark
 
#38 ·
Well today I pulled fuse 41 from the front fuse block and no change just like we thought because I don't have the npp option. Anyway I guess my only option now is to physically remove the valve from exhaust system. To bad I just sold my floor jack. Anyway if anyone has done this please give me some tips on how to do it in the most economical way. Aloha, Mark
 
#39 ·
Mark, don't do it. The valves you still have in place are for AFM, and people have done what you are thinking, and they said the droning sound was very bad.

Look for other aftermarket options are the suggestions I have heard for the non-NPP cars.
 
#40 ·
Thank you for you're input. I just love the way it sounds in the morning cold start. It sounds awesome. I found another link today to a site where someone else took their C7 in to add power and they actually blew up the motor on the dyno machine. That is going to be a law suit. I was looking for the c7 legend for the front fuse box when I saw the link. Anyway I will try to look through my history to find the link. The guy that was tearing it down was very detailed and took a lot of photo's of the whole process. I'll let you know if I find it. Aloha, Mark
 
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