powdrhound

Anyone know the reason for check valve #16 in the diagram below? Obviously if the #16 check valve is stuck open, you will have a boost leak as a result of it. If stuck closed, it should not really effect anything from a performance standpoint (but will have a negative effect from an emissions standpoint?)

What is the actual reason for the #16 check valve there? I gather that at idle, it allows fuel vapors from the EVAP canister to be sucked in thought the valve and into the throttle body (which is creating vacuum at idle) to be burned by the engine. When on boost, the valve is naturally closed and fuel vapors will get sucked in though line #19 which connects to the intake just ahead of the drives side turbo. On boost the pre turbo intake will have vacuum which will provide sucking action through line #19.

The reason I ask this is that I believe I have a faulty EVAP purge valve (#14) which is tripping the P0444 code (which point to a faulty #14 valve). Since getting the P0444 code, my hot idle has been a bit erratic also. On hot engine start up, it has actually stalled a couple of times and struggled to settle into a smooth idle. Curious how all this may be related. I will be changing the #14 purge valve and may change #16 also since it's right there. I was just curious if anyone actually understands or can explain the workings and reason for the #16 or #14 valves with any kind of certainty. When is the #14 valve commanded closed and open by the ECU? My assumption above is based purely on looking at the diagrams.

I posted the same question on 6bling but all I got was crickets. Smart guys, tuners, chime on in please, here is your chance to shine!



[url=https://flic.kr/p/SXvZXB]

BauerR

Honestly, I would just change them both. Assuming theyre still original to the car, your engine bay especially, is a torture chamber. If they haven't failed already, they probably will. Its a simple and cheap job.
When I installed the IPD plenum, I replaced every valve I could get my hands on. I think its was 5 in total. Plus all the soft lines.

powdrhound

I'm changing both even though pretty much all the valves were changed (except #14) when my engine was built 2 years ago. Every hose was changed for sure. It's not really a question of whether to change them or not but rather one of understanding the purpose and workings of the two valves. I'm trying to get a thorough understanding of the system, which no one really seems to have a grasp of.

garrett376

It looks like you answered your question about the #16 check valve above. The issue I had with check valve #16 is that it intermittently stuck which made it hard to diagnose as the car ran great for the most part, but when the valve was sticking, the car acted exactly like yours: hot idle it would just about stall, and sometimes did stall, tripping PSM/ABS errors at the time (I was told because the voltage drop from the very low idle). My intake wouldn't maintain a pressure test either when the valve was stuck open but not when it was working properly. Valve #14 can be cycled to confirm if it's working - a PIWIS can do this and I'm sure applying voltage to it will work also. But #14 is "closed" when off so unless it's completely failed open it would no allow an air flow leak to kill the idle; valve 14 should hold vacuum when not activated. In my case, literally sucking and blowing on check valve #16 confirmed its intermittent sticking problem and its replacement cured the stumbling.

garrett376

Carbon canister vapor load percentage primarily dictates when the ECU purges the tank.

powdrhound

Thank you very much for your input. The reason I started digging around is due to the fact that I have recently had a CEL pop up with the following P0444 fault code: Porsche fault code 98 - Tank Vent Valve.

I am attaching the Porsche P0444 troubleshooting PDF at the bottom here. Do you by any chance know which valve the document is referring to? There is a bit of a confusion whether it's the purge valve on the engine or the purge valve on the EVAP canister itself. The document call it a purge valve in this case.

Then take a look at post #22 in the following thread. You can see that that Porsche fault code document (at the bottom of the post) actually also refers to the valve as a "tank vent valve" (highlighted in blue). So the question remains, which valve is P0444 pointing to? Thank you...

http://www.6speedonline.com/forums/9...e-p0444-2.html

garrett376

In the DME 7.2 and 7.8 Diagnosis documents, the "EVAP canister purge valve" is the one on the intake that is between the canister and the engine intake - #14. The one on the canister is sometimes referenced as "operating purge valve".

Unlike the DME7.8 document, the DME7.2 document actually "defines" the Evap Purge Valve at the start of the P0444 chapter as follows:
I'd hook up a vacuum tool and confirm it (#14) holds vacuum when off. If it is mechanically broken it can permit air to pass, acting similar to a failed check valve #16 (unmetered air allowed to enter the turbo inlet pipe causing poor idle).

"02996ttx50

in theory, one could replace them faster than most can understand them.

Jferrante

great point - love new avatar!

"02996ttx50

ha thx.. well when the kinks sang about 'lola", it wasn't about a car ..

all this talk has me wanting to check my #16 again though. i do have another leak.. argh....

Joseph Caruso

Can anyone tell me if my 2004 996 Turbo had a vapor purge valve in the canister itself? I took off the right fender well and located the two valves towards the headlight. I checked both with a 9 volt battery and both were going and looked at the charcoal canister but didn't see the valve? Did I just miss it or do I need to remove it to see the valve? Thanks guys for all the info. I like the challenge and having you guys with the info and knowledge it's kinda fun troubleshooting ! Joe

powdrhound

There is no valve in the canister on the US cars. Only ROW cars..