^^^
Yep see my post #38 with pics of the butterfly's. The V4 are fully open on V8 Mode. They close as they did in the C7 so when in V4 they provide some back pressure and it doesn't sound like a V8 missing on 4 cylinders!

Note the small holes the exhaust has to pass though.

PS: Nice pics.

Repeating the Butterfly part of the valve pic.

 

Yes, I did see that. Where did you get those? Are they from the C7 or the C8? I any case, the C8 Service Manual describes essentially what you have pictured. It says that the exhaust must flow through a hole machined in the plate. It does say "A hole" (no pun intended here), rather than two holes or holes - so if your photo is of the C7 valve, it may be that the C8 looks a little different.

I have been looking at the schematic and thinking about how the system determines that a exhaust flow control valve is disconnected or not functioning correctly. I noted that there is what I called a control path from the AFM valves back to the fuel pump power control module - there is little switch symbol in each of the actuators in the lower left, with a square wave/pulses symbol, and with a ground symbol, and wire then going from that switch symbol back to the fuel pump power control module. That could be (alert - speculation here) the path by which a AFM exhaust flow control valve error is detected. The tailpipe exhaust flow control valve does not have that same feeback path - so maybe it does not detect a valve error. That does not mean it can't detect when the connector is disconnected (it must since we have simulators). But what if you just removed the actuator (as shown in the photo), and leave the connector connected, and then wire tie it out of the way? The connector to it already appears to provide the ground (pin1). I am 50/50 on that - an idea to try - it could be that something detects the "travel" in the actuator via the existing power or control path (that may be what "relearning" the valves is about).

 

^^^
That was a pic from someone who dissected the C8 exhaust. I recall from the description of the C7 NPP, Tenneco (one of my good customers for welding stuff) used a stepping motor that sent signals back to define it it was open or closed. I know for the C7 IF the V4's were disconnected it tripped a CEL. With the NPP valves you could pull a fuse and no CELs. That is what Mild to Wild does. It uses a remote relay to essentially "pull the fuse or reinsert" with a switch.

Also though I had mentioned mechanically disconnecting and just let the motor think it was doing it's thing! However on my C6 (which did not have V4 and the valves operated with a Vacuum (exhaust was also made by Tenneco) there was a drone at highway speeds. Bad enough that even with the sound system playing it was objectional and I would flip my manual toggle switch and put the valves back in the system to close. Drone might be an issue with the C8.

PS: Would think two holes would avoid exhaust gas putting pressure on one side.

 

watch this video starting at 1:11 ->>> 2:40
​​​​​​

 

Jerry, seems to me you may have mentioned that you have a service manual for the C7? If so, could you post the equivalent schematic for the exhaust flow control system - that is - the C7 version of the schematic I put in post 40 for the C8. Then we can see if, and how it differs.

 

I went thru the pages in the index referencing the exhaust. The paper Manul has line drawings NOT nice sketches. None that I saw re the C7 for what you asked.

These are what I have in my pic file since this came up often: