fnckr

See pic below please. What is inside the area where the hose branches off? Need a part number or explanation of what this is please. It connects to COV 1. This is NOT the sound symposer flap, that connects to COV 2.

There is a rattle inside of this, so something is broken. A quarter turn counter-clockwise allows the circular part to come out. Attached is a rod with a small gear at the end. If I can’t get the part to replace it, do I need to worry about it? In other words is it for sound purposes only, and not emissions or performance? BTW, the area is sealed off from the actual air box. Therefore, I believe it is a Helmholtz resonator.

Perhaps a technician broke it previously, while removing the airbox, and didn’t bother to fix it.

fnckr

It is the Helmholtz resonator. While it is not necessary to the function of the airbox, the vacuum actuated mechanism and flap is NOT removable or replaceable. The box itself is glued together after the mechanism is installed. Twisting the actuator and pulling it out will break the posts on the flap. Then the flap will rattle useless inside the box.

The missing quarter chunk on the flap is from me pulling it out of the branched hose opening. Only one of the posts was broken prior to my attempt to remove the now useless flap.

Is is a very common mod to delete this flap on the 996 and 997 air boxes. According to an SAE article posted on another forum, this “tuned” resonator is used in conjunction with the sound symposer. As I have also deleted/blocked the sound symposer, I will just leave this flap in its current open/non-existent/removed state. Also, I therefore have two useless COV that I will also be plugging. In another thread I will ask if there is a way to delete the COVs with perhaps a resistor for the wire harnesses (I’m no electrical expert).

Jack F

What year is this?

fnckr

It is a 2013 C2S. I planned to replace all of the COVs while I am doing the 40k service. Being very comprehensive with new coils, belt, etc. If I don’t have to replace these two change over valves, then I’ll have two extra. Too bad they are the easiest to reach...

worf928

I found this thread via a search, looking to confirm what I’d tentatively concluded: that vacuum actuator is part of the sound symposor.

Why was I searching? To figure out if I could just cap the vac line from its change-over valve.

Why? Because there’s a spring-loaded rubber diaphragm (that’s how vacuum-actuated stuff usually works) inside that gizmo. And the diaphragm in CarChick’s 991 has a slash in it. So it won’t hold vacuum.

Why is this a problem? Because if any of the vacuum-actuated gizmos has a vacuum leak you will eventually get 1432 and/or 1433 codes. (Cooling system fault.)

In the 928 world we replace the rubber diaphragm.

But, in the 991 world? Naw… wegotsta replace the business end of the air box.