B-STOCK

I know very little about the automatic cars but just found out that when gear selector is in drive you automatically run in the 4-8 cylinder deactivation mode. I was very surprised this was the case. I have a manual and pulled the fuse until the mild to wild came out and installed one. Call it wife mode. Back to the question. On a manual with the fuse pulled I believe the valves still close when in Echo mode. There is no sound at all even with the fuse pulled so there must be some control still engaged. I never use the mode but tried it to see if something still closed the valves even with the fuse pulled. So if the fuse is pulled in the auto cars do the valves close when it changes to the four cylinder mode? I would think so.

PJay

By pulling the fuse, you've removed all power to the valves. So, if you haven't installed a Mild-to-Wild in it's place, they can never close. It doesn't matter which transmission you have, the valves operate the same way.

Red Mist Rulz

There are TWO sets of valves. Pulling the fuse (41 or 42, depending on year) forces the valves behind the mufflers, commonly called the NPP valves, to remain open.

In front of the mufflers there are two additional valves, commonly called AFM valves, which close partially when the car is in V4 mode. (How much they close depends on multiple factors, including rpm, throttle opening, and more.) Pulling fuse 42 has NO effect on these AFM valves. So even with the NPP valves wide open, if you go into V4 mode the exhaust will get quieter.

The AFM valves are controlled by fuse 32, IIRC, but if you pull that fuse you'll get a check engine light (CEL). In an automatic, the only way to keep the AFM valves from closing are to put the transmission into manual, paddle shift mode, use an aftermarket device like the Range Technologies AFM disabler, or do a tune which deletes the AFM activation code. But note that a tune can give GM grounds to deny engine and drivetrain warranty claims.

B-STOCK

Ok the AMF valves quiet down the exhaust in 4 cylinder mode. So if you have a manual tranny car it won't go into ECHO mode unless you dial it in but if its a auto and in drive and goes into 4 cylinder mode you get hardley any sound. From what I understand there is no way to keep a auto out of 4 cyl mode unless you keep the tranny in manual mode. My friends asked me if there was I fix for that because they don't want to ever go into 4 cylinder mode but don't feel like always paddle shifting the tranny.

Foosh

The other fix is the aftermarket AFM Range Disabler, or it can be tuned out. A tune will cause a powertrain warranty block, so the Range Disabler is safest option.