OK smart people, looking for some help here. I have a 2026 HTC Z06. I am wanting to install a wireless exhaust valve controller so I can control the valves being open or closed via one of the Homelink visor buttons. I did this very thing on my 2019 Z and it worked perfectly. I removed the one I made for my C7Z and want to reuse it on the 26Z. Fuse cover says that fuse 21 of the rear compartment fuse block (the one between the seats) is for the "Exhaust Valve Solenoid". This particular fuse is a micro3 fuse (2 fuses in one port). Looking at the fuse (see pic), the center terminal is common, the left terminal is Fuse 20 and the right terminal is Fuse 21....at least it is supposed to be. Removing the fuse reveals copper terminals for the center port and the left port (which would be Fuse 20), but no terminal for the right port (see pic). So there is no circuit for "Fuse 21". The valves do open and close when I change the setting on the infotainment center, so I know the there is a circuit somewhere controlling the valves. I guess the fuse cover and all the internet info is wrong about Fuse 21? What am I missing here? Thanks in advance!

 

Looks like F20 is correct


2023 Stingray NPP Schematic:

 

Actually, I take it back. Looks like F20 is the 12v ignition power source feeding the relays, and it should be hot when the vehicle is on (even if the valves are closed)

The relay control signal comes from the Fuel Pump Power Control Module ...

 

2nd apologies ... LOL

I gave you the LT2 schematic above and just realized you have the LT6 (Z06)

Here is the LT6 schematic. Looks like F13 is the 12v power source for the relays and the control signal still comes from the Fuel Pump PCM


2023 Z06 NPP Schematic:

 

For comparison, here is the NPP schematic for the 2019. Looks like the 2019 did not have the feedback circuits like the C8 has; so using the same solution to override the NPP valve position will most likely cause a fault due to the signals coming back on pins 16 and 17 will not be correct.The feedback signal on pins 16 and 17 shown in the C8 schematic doesn't appear on the C7 schematic.


2019 NPP Schematic:

 

Thank you!!! Making sense now.......Fuse 13 is listed as "AFM".....the LT6 does not have AFM, so they must be using Fuse13 for the "sound valves". Fuse 21 does nothing for the LT6. Will verify this tomorrow.

EDIT: I see what you saying regarding data for pins 16 and 17. I am hoping just removing power will default the valves to open and not trip a code. We will find out.

THANK YOU!!!

 

F13 RA in the C8 is equivalent to F87 UA in the C7 (supplies 12v source power direct to the actuator valves)
F22 RA in the C8 is equivalent to F20 RA in the C7 (supplies 12v source power to the controlling module - Fuel Pump Control Module on the C8 / Chassis Control Module on the C7)

The fuel pump PCM is signaling the actuators on a C8, but the chassis control module is doing this on the C7.

Which circuit were you tapped into on the C7, F20? So you were killing power to the chassis control module to force the valves open?

You can try F22 on the C8 I suppose, but it's going to kill power to the Fuel Pump PCM, which is probably going to cause issues.

You might need a different solution for the C8 than simply interrupting the power going to the controlling module; especially since in the C8, this is the Fuel Pump PCM.

You can kill the source power to the actuators by interrupting F13 like you're suggesting, but note the feedback signal on pins 16 and 17 not being as expected will probably trigger a fault condition.

 

On my C7 it was fuse 87 (Engine Compartment Fuse Block). Just killed 12V to the valves. So I going to guess Fuse 13 on my C8Z will do the same thing as Fuse 87 on my 2019Z.

 

delete

 

Then F13 is the equivalent and should work.

You might need to see what pins 16 and 17 on the Fuel Pump PCM harness are reading when the valves are open, and then modify your solution to trigger the same on these wires when you are overriding it (to avoid the PCM thinking something is wrong).

P16 and P17 might be a PWM signal, so be sure you're looking fr that and not just a voltage reading.

 

Good idea. Thanks again for the help and info, VERY helpful!

 

@Stoopalini , since you have a version of the manual the covers Z06, is there a description of how it works in the Z06? I have read that the Z06 allows for variable valve positions, unlike the Stringray which are open or closed. The control has always been via PWM, so variable valve positions are possible if the actuator can support that . You can see the little square wave symbol on the schematic which I think is their symbol for a PWM signal. Even in my 2020 manual it explicitly says its a PWM signal.

On a related note, at least on the Stingray, folks have experimented with keeping the valves open all the time, versus the track setting of engine sound which also keeps the valves open almost all the time. And the difference, if any, was disappointing. The valves only close in a narrow region of rpm, speed, and throttle angle to meet Federal bypass standards, and under that condition there is not very much exhaust noise anyway - so its difficult to tell the difference. Don't know if it would be the same on Z06.

See post 1 at this thread:
https://www.corvetteforum.com/forums...ld-2-wild.html

 

Yep, I installed a simple switch in my 2008 C8 NPP to keep the NPP Valves open all the time. Was simple. BTW had to let them close when on highway at 65 to 70 mph or there was a bad drone!

Was a bit more difficult in the C7 as fuse instead of behind the passenger footwell carpet was in the engine compartment. Rather then run a wire and use a switch, many used a remote relay (Mild to Wild) operated by the remote supplied OR HomeLink. It worked. Didn't do much BUT worked.

Since in the C8 the fuse operating NPP is behind the waterfall thought easy to install switch. So in 2020 for my C8 made a sketch on how it could work. The fuse is a two circuit fuse so would blow one section of the a two way, three prong fuse on the NPP side and install a switch. Someone took me up on the idea in 2020 and it tripped a CEL!

Mild to Wild came out with a device that said it worked BUT it tripped a CEL. Someone them forced the issue "CEL and all" and found little difference. Fact is the short coupled headers to CATs to muffler are NOT as loud as C7's with long pipes. The Exec Chief Corvette Engineer when the C8 was introduced explained why.

As ​​​@Andybump noted the C7 and C8 electric stepping motors for both V4/V8 valves AND NPP are either open or shut (the V4 butterfly valves have small holes that restrict flow when closed.) They have feedback circuits if not in the correct poston they send a signal back and CEL.

The c8 Z06 actually allows the valves to partially open, works with the Helmholtz intake manifold valves intake. So perhaps different.

Good Luck!

 

Jerry, I have seen this stated before. But where does that information come from? Is there a Service Manual description of it, or even something in an ad from GM?
And does it only apply to Z06, or does it also carry over to Eray?

 

As I recall it was discussed when they defined how the Helmholtz Intake helped flatten the torque curve. But this text and Pics from Hot Rod Mag 2/22/2022 just talks about exhaust sound. Think it's just a Z06 thing.

 

Thanks! Now if we could just find description of how it works with respect to the engine sound settings. For Stingray, Sport or Track settings of the engine sound have nearly the same behavior. Open at idle and open under most driving scenarios. Only closing to meet Federal Bypass Standards. The difference between them (we think from owner tests) is just the range of rpm and speed where they close. Certainly with the variable position valves on the Z06 they could have more variation if they wanted to.

 

What's the advantage of this versus just selecting the exhaust valves/volume setting (4 different options) right from the infotainment screen?

 

Advantage of the variable valve positions?

What we have on the Stingray is really only two volume levels - the valves are either open or closed.
Stealth - closed all the time.
Tour - closed at idle and almost all the time except for aggressive throttle. Then fully open.
Sport - open at idle and open almost all the time. Close in a narrow band of speed, rpm, and throttle that is not disclosed.
Track - open at idle and open almost all the time. Close in a narrow band of speed, rpm and throttle that is not disclosed, but is little "narrower"

With the variable valve position, instead of just two volume levels, you can "more adjustability" in each drive mode if you consider that an advantage. I think before we can say more about its "advantage" we need to know more about what engine sound settings that Z06 had, and how those settings affect the positioning of the valves. Without the information its just not clear (to me anyway).

 

The manual I have access to does have Stingray, Z06 and eRay specific pages, but all 3 look the same to me (see attached)



I think he meant what is the advantage of having an override switch (like using the Homelink or a hard-wired switch) vs just using the built in controls to select track exhaust mode.

 

In my C6 Z51 NPP where I added a switch to keep open all the time AND folks who added a Mild to Wild system in their C7's proved what I found in my C7s and believe the C8 set at max (Track) for NPP is the same:
The NPP valves in Track are closed below ~1700 to 1900 rpm. Partly to eliminate drone on highways speeds AND to meet drive by max exhaust sound laws.

So they open past 1700 to 1900 when NPP is set to Max (Track) and from C7 data stay closed until 2500 rpm in Touring.

One reson IMO the exhaust is too quiet for me in normal driving. Yep hear at WOT but in the E-Ray that's only a few seconds and your past tripple dgits!

My C6 where I installed a switch to keep open is a good example. Had to let them close at 60 to 70 mph on highway or drone was objectionable!