UPDATE: I'm adding links to couple of documents from Porsche specific to the article below....
I've come across soooooo many posts online asking questions about vacuum lines, exhaust valves, change-over valves and related that I thought I'd put together an overview with some pictures and illustrations....
Probably the 2 most prevalent discussions about the vacuum system in the 991 are centered on Change Over Valves (COVs), and periodic "failures" that 991 owners have reported (myself included!). Also keep in mind that the S cars, and cars with Porsche Sports Exhaust (PSE) rely on COVs to open-and-close the exhaust valving.
Here is a link to one of the Rennlist 991 conversation threads that covers COV failures / replacements: "
Heater quit working again" Search Rennlist, as well as the 6Speedonline boards, for more details....
Here is an illustration and picture of the COV part:
1. Fresh Air Connection
2. Vacuum Line for the Actuator
3. Vacuum Connection
Here's a pic as posted on Rennlist 991 forums by member STG:
As you can see in this picture, the part # is clearly visible imprinted on the side of the device.
Schematic, showing the basic relationship of each COV and vacuum...
The above schematic is straight from the official Porsche Service Information Book, and posted to 6SpeedOnline forums by member SM_ATL. I'll get more into the vacuum line routing later in this post.
As for how many COVs are on a 991 (MY2012.5 through MY 2016), # ranges from 7 to 10 per below:
1. Air Cleaner Flap
2. Acoustic Simulator
3. Heater Shut-Off Valve
4. Exhaust Flaps
5. Coolant Shut-Off Valve on Engine Bypass Circuit
6. Tuning Flap
7. Shut-Off Valve on Heat Exchanger for Gear Wheel Set Oil
8. Shut-Off Valve for Clutch Fluid Heat Exchanger (PDK ONLY)
9. Tuning Flap (cars with full X-51 Power Kit ONLY)
10. Tuning Flap (cars with full X-51 Power Kit ONLY)
#9 and 10 are not a mistake on my part.... cars with X-51 option have multiple tuning flaps apparently.
And here is an illustration from Porsche with locations of each of the COVs listed above:
The most common complaints of COV failures are the Exhaust Flaps and Heater Shut-Off Valve. As a 991 owner I've experienced multiple failures of both....!
Here are some vacuum line routing illustrations:
For PDK cars:
For MT cars:
Exhaust Flap line routing....
In the above, the top part of the picture is the 3.8 standard exhaust, whereas the bottom-half of the picture is for the 991 with PSE option.
Based on feedback from nearly all who've posted to 991 enthusiast forums on the topic of COV failures, it seems that no matter what the root cause, the service departments at dealers will NOT proactively replace COVs that haven't failed yet. There have been multiple part # revisions, perhaps indicating attempts at mitigate future failures -- but other than a brief campaign for the earliest MY 2012 991s there has NOT been any recall or service bulletins to replace suspect parts. The SB that I refer to here is #TI-64-12 and NHTSA ID #10048760 if you'd like to look it up.
If you'd like to replace yourself, know that there isn't a WM specific to the procedure. However, there is WM 2400IN, which provides a lot of good pictures and location detail.
I'll continue to compile other COV resources, and post updates from time-to-time. Contact me, or comment below, if you have questions or want to share any other experiences of your own! Thanks!
