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Since this thread has managed to stay relevant/cited for so long, I want to keep a reasonably concise list of the collective knowledge from this thread and others. I will update it so that it's easier for people to get the details without parsing the whole thread.
***I have owned a 2014 Z51 M7 NPP for over a year, and now own a 2015 Z51 A8 NPP.*** So I have plenty of personal seat time with both Stingray transmissions WRT NPP behavior. Here's a summary of what I think we collectively figured out in the numerous threads. All details are important, however some caveats follow.
UPDATE 9/30/2015: I had the opportunity (surreal quite frankly) to meet Tadge and Harlan at a private event today. I spoke privately with the two of them for about 10 minutes, and one of my questions was the NPP programming. Tadge's comment was something like "If we didn't do it that way, we wouldn't be legal". Meaning that even in Track mode, the valves need to close for the dB requirements in the FMVSS pass-by noise regulations.
meyerweb (in post #252 in this thread) figured all this out a while back and is 100% correct that the NPP programming is architected around the FMVSS pass-by noise regulations.
All C7 have valves for V4 mode in front of the mufflers. We call them AFM valves. Fuse 32 controls the AFM valves, and pulling fuse 32 or AFM connectors will result in a CEL and awful sound in V4 mode.
NPP cars have electronic valves in the outer exhaust tips. We call them NPP valves. Fuse 41 (2014) or fuse 42 (2015+) controls NPP valves. Pulling the fuse will NOT cause a CEL, nor will pulling the connectors at the valves. These two NPP valve disable methods are electrically identical, but the fuse pull is simpler and more easily reversible.
Manual transmission cars go into V4 mode ONLY in ECO mode.
Automatic cars go into V4 AFM mode in ALL MODES, except when paddle shifting/sport shift.
The Z06 and newer 2015 Stingray have new Engine Sound Management (ESM) settings! ESM Off (2014) = Track (2015+) in the below. The Engine Sound Management in the latest settings implementation on the newer 2015 Stingray and Z06 (see below) are progressively more aggressive (valves open earlier and longer) than the original ESM settings available (originally only Auto or Off, and some early 2015 M7 still have the original menu).
Engine Sound Management (ESM) OFF/Track will NOT keep NPP valves open all the time for the 2014-2015 Stingray. Even with the ESM menu update to the 2015 ESM settings, and even in the OFF/Track setting, the NPP valves will still actuate by design in certain situations (low RPM, lugging, high gear highway, etc.).
M7 very pronounced below 1700RPM in 3rd gear and above. M7 owners call this the "1700RPM hitch".
A8 is inconsistent in ESM Off/Track. There is a hitch below 1900RPM (observed in my car) even in V8/paddle mode where the NPP will very frequently close in normal/leisurely driving on upshifts in gears 5 and up. It's like a pre-AFM buffer even though engine is is V8 mode. In ESM Off/Track when the NPP have closed, I can tip into the throttle gradually, and as soon as I hit 1900RPM the NPP will open. This is entirely while in V8 mode. When I pull the NPP fuse this goes away completely at the cost of much more audible transitions between V4/8. I need to get a video of this as it's not easy to describe.
Driving Mode (dial) does affect NPP behavior with Engine Sound Management (ESM) on Auto. However, that's subject to most of the below when OFF or in Track in the newer ESM mode settings above.
Driving Mode does not alter sound when NPP valves and AFM valves OPEN during V8 operation. This is the loudest the NPP exhaust can be both at idle and while driving, and Driving Mode doesn't change the sound when both sets of valves are open.
The awesome raspiness at cold start is not an NPP function. It's a fueling and ignition condition that only exists at cold start (unfortunately) that quiets down to 'normal'. Fuse pull or ESM setting will not change this.
V4 operation will close the AFM valves and make the exhaust quiet even with NPP valves forced open (fuse 41/42 pulled). This is the biggest reason A6/8 owners may feel the NPP exhaust is 'too quiet' off throttle since it can spend so much time in V4 mode.
In M7 Stingray cars, pulling NPP fuse fixes ONLY the 1700RPM hitch that some (like me) find annoying and prevents NPP valves from closing at highway cruise even with ESM OFF/Track.
NPP valves open all the time and V8 operation will result in hearing/feeling more low frequency content at low RPM all the time (highway especially). Some may like this, some may find this 'drone' objectionable.
Once NPP fuse is pulled, ESM obviously no longer has any effect, so you give up push button 'stealth mode'.
In automatics, pulling NPP fuse has a very different effect due to nearly constant V4 operation in low RPM/low load conditions. It gets quiet when AFM valves close...and therefore it's quiet even with NPP fuse pulled or in ESM OFF/Track. The automatics DO have a hitch at 1900RPM, but it's inconsistent as noted earlier in this list. It also makes the V4/8 transitions much more audible.
Disabling V4 in automatics outside paddle/sport shift requires a tune or Range Technology OBDII plug (http://www.rangetechnology.com/).
All the intricacies of the above essentially mean that the M7 and A6/8 folks will have a different experience with the NPP. I feel the M7 Stingray owners will really notice the difference when pulling fuse 41/42, but you give up some control. It's worth a try though, IMO. Automatic owners will hear little or no difference between ESM OFF/Track and fuse 41/42 pulled. This is due to the automatic's nearly constant V4 operation off throttle/low RPM/low load in all driving modes. So I personally don't think pulling fuse 41/42 makes much sense for auto owners.
The location for 2014 & 2015 is the SAME. Only the number of the slot is different (thanks Theta for the image!):
In post #243, meyerweb did some extensive testing of his '15 M7 Z51. Some notable similarities and differences. Read here for more:
My remote switch box was a little different in that the two case halves were the same height. I also used a regular round ground wire, but it was a plenum rated jacket from another project of mine. I routed the ground wire out the notch that already exists in the lid. I also made sure the ground wire had a "low loop" after exiting the fuse box so water would have to travel "up" to get to the seal.
My mounting for the transmitter was on the pop-up 12V face. Nice sticky 2-sided tape.
This solution is FANTASTIC!
Overall install:
Ground wire going out the existing notch in the lid:
Remote location:
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The 'original' OP:
UPDATE 4: For this past week, I have set Engine Sound Management back to Auto with fuse 41 removed in order to validate no CEL in this mode as well. Driving in Tour and Sport, no CEL. I was concerned that constant calls for the NPP to be closed in these modes (rather than just the 1700RPM hitch in ESM Off) may cause an issue. This is also important since any external switch would want to rely on ESM Auto as the base state which the switch would then override for 100% open NPP.
UPDATE 3: Fuse 41 only pulled for a week. 3 trips to and from work and about 8-9 start-stop cycles. NO CEL!!! All this really solves is the 1700RPM NPP issue. What you give up is on-the-fly changes to Engine Sound Management, so 100% open NPP all the time. V4 mode is unaffected.
I have only been operating in Engine Sound Management OFF. Not sure why it would make a difference in CEL if set to AUTO, but I wanted to mention it.
I like it better, but I can understand why the NVH guys may have done this. The bass resonance is noticeable in the upper gear tip-in lugging as described previously. However, I like it better as I can hear what the car is doing all the time.
So it -appears- that the LED fuse may not be necessary to prevent CEL. Theta's control box would be the long term solution.
UPDATE 2: CEL cleared when fuses replaced and restarted about 5 times.
Fuse 41 controls the NPP rear valves. With 41 gone and 32 in place, Engine Sound Management has no effect. I will assume for now that 32 is the front V4 valves.
Will try driving without 41 only and see if it throws a CEL. I suspect it will since I recall another member got one when his NPP valves froze in really cold weather.
UPDATE 1: Got a CEL on the way home. Replaced fuses and restarted a couple times. CEL Still on. Will give another couple tries tomorrow to see if it clears before calling OnStar. Hopefully it's not a coincidence with a real CEL.
V4 mode is very coarse sounding. A bit like a tractor. Sound seemed to noticeably increase interior vibration and seat resonance at highway speed. Added unpleasant booming.
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Original post:
Cliff's Notes version: pulling fuses 32 and 41 in the front fuse box (engine) leaves BOTH the front and rear exhaust valves open for all driver modes and V8/V4 modes. No CEL.
I had read here and another forum about this trick, so I tried it today to see what happened. The C7 manual (page 10-39+) shows fuses 32 and 41 control exhaust valves 1 and 2...so I pulled them.
I have an M7.
Observations:
Engine Sound Management selections have no effect, as expected.
V4 mode sounds crappy. Forced it to V4 in Eco mode...and switched out 5 seconds later.
The behavior on low RPM throttle tip-in (on upshifts especially) where the sound is quiet and then valves open at about 1700 RPM is gone. Again, as expected.
There was no CEL thrown in my drive to work (~35 minutes).
There -may- have been more drone on the highway in 6-7th in V8 mode, but I need to pay more attention and update this comment. The reason I am doubting myself on this is it would imply some sort of closing of one or both sets of valves in normal "open all the time" operation.
So the experiment was a success, but I am not sure if I will leave it this way. For me personally, the only minor annoyance of the standard NPP "open all the time" setting was #3 above; it was too abrupt and on/off for my tastes. Not that big a deal, since with the fuse pull V4 mode is not nice and there no -option- of going quiet while driving.
I think the A6 folks would not like the results since, from my understanding, V4 can happen in most/all modes (maybe except Track?). For M7 folks, stay out of Eco. Of course if you tune out V4, then it's not a problem.
Last edited by xp800; 05-22-2016 at 11:21 AM.
Reason: Tagde NPP confirmation, Skidplate wireless solution
Cliff's Notes version: pulling fuses 32 and 41 in the front fuse box (engine) leaves BOTH the front and rear exhaust valves open for all driver modes and V8/V4 modes. No CEL.
I had read here and another forum about this trick, so I tried it today to see what happened. The C7 manual (page 10-39+) shows fuses 32 and 41 control exhaust valves 1 and 2...so I pulled them.
I have an M7.
Observations:
Engine Sound Management selections have no effect, as expected.
V4 mode sounds crappy. Forced it to V4 in Eco mode...and switched out 5 seconds later.
The behavior on low RPM throttle tip-in (on upshifts especially) where the sound is quiet and then valves open at about 1700 RPM is gone. Again, as expected.
There was no CEL thrown in my drive to work (~35 minutes).
There -may- have been more drone on the highway in 7th, but I need to pay more attention and update this comment. The reason I am doubting myself on this is it would imply some sort of closing of one or both sets of valves.
So the experiment was a success, but I am not sure if I will leave it this way. For me personally, the only minor annoyance of the standard NPP "open all the time" setting was #3 above; it was too abrupt and on/off for my tastes. Not that big a deal, since with the fuse pull V4 mode is not nice and there no -option- of going quiet while driving.
I think the A6 folks would not like the results since, from my understanding, V4 can happen in most/all modes (maybe except Track?). For M7 folks, stay out of Eco. Of course if you tune out V4, then it's not a problem.
Great info, thanks!
And yes, the A6 will go into V4 in any drive mode unless it's in manual/paddle shift mode.
Curious how crappy it sounded in V4 mode...
S.
So the experiment was a success, but I am not sure if I will leave it this way. For me personally, the only minor annoyance of the standard NPP "open all the time" setting was #3 above; it was too abrupt and on/off for my tastes. Not that big a deal, since with the fuse pull V4 mode is not nice and there no -option- of going quiet while driving.
This has the wheels in my head turning... I hate having to be in Race mode to have the exhaust sound like I want it to. In sport, the tip in is just too much.
There is an opportunity here to create something similar to the Wild2Mild using a wireless on/off relay to enable/disable the fusing on the fly.
A simple on/off button setup like I have on other cutouts would essentially lock out the control by disconnecting the fused link when you have the flaps open. To make it quieter, just hit the on button to re-establish the fused link.
Hmm... Yet another project I don't have time for, but sounds like it could be cool, and truthfully isn't that hard.
Actually, screw it - I'm going to move forward with that idea and see how it turns out. Might be something that solves problems like that, since it sounds like we're in the same boat.
NPP is nice, but I wish we could re-calibrate the tip in from the BCM-side. No such luck cracking the BCM yet, and I know several of us have been working on it.
I had been thinking the same thing too. The complication I see vs. the typical M2W is that this is the engine compartment fuse box, not the one in the rear compartment.
The lid snaps tight and there seems to be little space inside the box, and anything you do needs to be really waterproof and heat resistant. You could certainly remote the relay/receiver/switch inside the car or with its own waterproof box. But I -think- you'd need to pass a minimum of 5 conductors out of the fusebox to maintain 2 independent switched circuits plus ground.
I'm sure you will think better "outside the box" than me, and I look forward to the results!
You're right about the lid. I'm wiring a wideband to the box for temporary use during tuning, and there's very little room in there.
I think I might have a solution, but it will be kind of a hack job until someone comes up with a more proper and marketable solution. This will just be for kicks after seeing your post - thanks for that.
UPDATE 1: Got a CEL on the way home. Replaced fuses and restarted a couple times. CEL Still on. Will give another couple tries tomorrow to see if it clears before calling OnStar. Hopefully it's not a coincidence with a real CEL.
V4 mode is very coarse sounding. A bit like a tractor. Sound seemed to noticeably increase interior vibration and seat resonance at highway speed. Added unpleasant booming.
Ah, interesting - I was wondering if a CEL would creep up.
Do you have a code scanner handy?
I do not...yet. Maybe it's the excuse to get the DS Trinity I've been vacillating about.
I will experiment more eventually. I am interested to know whether the fuses define front/rear or left/right pairs. I suspect it's front/rear since all cars have fronts and would need a fuse. NPP would add a fuse for the rears. If there's a way to tune out the CEL (assuming that what's caused mine), then the front V4 valves can stay enabled and pull/switch/M2W the rears.
UPDATE 2: CEL cleared when fuses replaced and restarted about 5 times.
Fuse 41 controls the NPP rear valves. With 41 gone and 32 in place, Engine Sound Management has no effect. I will assume for now that 32 is the front V4 valves.
Will try driving without 41 only and see if it throws a CEL. I suspect it will since I recall another member got one when his NPP valves froze in really cold weather.
Maybe someone can come up with a CAGS like plug that spoofs the sensor into thinking the NPP valves are there when the fuse is pulled. I'd bet it needs to see a load, but power dissipation may be a problem for a simple resistor given the current that's probably required to actuate the valves and keep them closed.
The elegant solution would be tuning the CEL trigger/sensor out. The Rube Goldberg would be a double throw switch that either runs the NPP circuit per design or dumps it thru a spoof plug and keeps them open all the time.
I can't see ever wanting the front V4 valves bypassed.
Maybe someone can come up with a CAGS like plug that spoofs the sensor into thinking the NPP valves are there when the fuse is pulled. I'd bet it needs to see a load, but power dissipation may be a problem for a simple resistor given the current that's probably required to actuate the valves and keep them closed.
The elegant solution would be tuning the CEL trigger/sensor out. The Rube Goldberg would be a double throw switch that either runs the NPP circuit per design or dumps it thru a spoof plug and keeps them open all the time.
I can't see ever wanting the front V4 valves bypasses.
That I can cover - the Littlefuse LED indicator gives a tiny bit of current but the BCM sees the load even though the fuse doesn't deliver the load.
That's been done a lot before, and is part of my plan.
03-21-2014, 10:28 AM
NPP fuse pull trick/result
