# Rear PCV explained??



## lagamm (Mar 25, 2006)

Ok I'm just looking for a confirmation on how our 2.0T FSI PVC system works.
As far as I can understand on my car (2006 jetta 2.0T) that I have a front PCV that will circulate crankcase gasses when under vacuum and will block pressure under boost (when functioning correctly)
(I plan on adding EJ fix)
the rear PCV is connected to the air inlet pipe into the turbo and is always under vacuum which continues to circulate CC gasses when the front PCV is under boost. 
the rear on is what I am unsure of. The reason I am asking this is I do not think a have rear PCV with intergrated valve and want to know what that valve is for? I checked my DV and there is no oil or tears. But if it is always under vacuum why would you need a check valve in it?
Being new to turbo engines I just want to know how everything works togther.(it's the engineer in me)
Also
I just got a nice bonus at work ($1850) and planning on doing 
1. revo stage 1
2. Eibach Pro w/ Koni FSD's
3. Forge DV
4. Neuspeed Intake
5. clear side markers
I'm going to drive down to NA motorsports (about 50min from my house) and pay cash for everything. My wife does not know about the bonus and no need to leave a paper trail, LOL!


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## rbradleymedmd (Feb 24, 2007)

*Re: Rear PCV explained?? (lagamm)*

I'm kind of curious about this as well. From my understanding there are two different PCV set-ups...
1. The Housing contains both front and rear check vavles
2. The Housing contains the front valve and the rear breather hose has a built-in check valve
Is it detrimental to run a combination of these two systems? Meaning is it bad for the engine to have the Housing w/ 2 check valves and add the breather hose w/ check valve built-in...combine this set-up w/ the Eurojet Front PCV Fix and that gives you a 4-check valve system? Would any problems arise from this set-up?

_Quote, originally posted by *lagamm* »_Also
I just got a nice bonus at work ($1850) and planning on doing 
1. revo stage 1
2. Eibach Pro w/ Koni FSD's
3. Forge DV *Hold off on this...if it ain't broke, don't fix it*
4. Neuspeed Intake
5. clear side markers
*6. maybe look to add a DP and go for stage II*


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## ZWStewart (Mar 27, 2002)

the front PCV only functions under vacuum. the rear pcv is the one that is important. The rear pcv use the intake vacuum to vent the crankcase under boost/load, which is when you will actually have some positive crankcase pressure.


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## lagamm (Mar 25, 2006)

*Re: (ZWStewart)*

So what you are saying is the rear crancase vent is under vacuun while the engine is in boost or under vacuum. Correct?
If that is correct why would i need a valve in the rear crankcase vent if it always is under vac.


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## ZWStewart (Mar 27, 2002)

*Re: (lagamm)*

The front PCV has a checkvalve that closes when the intake manifold is pressureized, and opens up when the intake manifold is in a state of vaccum. So, when the engine is under load and making boost, the front pcv is sealed off, leaving all the crankcase pressure to be dealt with by the rear pcv valve only. Others, as well as I, have ran our 2.0tfsi engine with the front pcv plugged, with great results. 
more details here.
http://deviantspeed.com/the-ultimate-20t-pcv-fix


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## lagamm (Mar 25, 2006)

*Re: (ZWStewart)*

Thank you for you explaination. I pretty much new all of that about the front PCV. Maybe I didnt explain myself!
My 2006 Jetta 2.0T has an old revision rear PCV w/no intergrted valve i believe. Looking at this ugraded factory peice that is updated.
Breather Tube
Breather hose on back of valve cover, common leak area, updated version with internal check valve









The question I am asking is should I update mine and why would you need an internal check valve if it is always under vacuum


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## rippie74 (Sep 26, 2007)

*Re: (ZWStewart)*


_Quote, originally posted by *ZWStewart* »_The front PCV has a checkvalve that closes when the intake manifold is pressureized, and opens up when the intake manifold is in a state of vaccum. So, when the engine is under load and making boost, the front pcv is sealed off, leaving all the crankcase pressure to be dealt with by the rear pcv valve only. Others, as well as I, have ran our 2.0tfsi engine with the front pcv plugged, with great results. 
more details here.
http://deviantspeed.com/the-ultimate-20t-pcv-fix


IIIInnnnterestinnnnnnnngggggg


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## crew219 (Oct 18, 2000)

*Re: (rippie74)*


_Quote, originally posted by *rippie74* »_
IIIInnnnterestinnnnnnnngggggg









Yep . . . if it doesn't work, just remove it.








lol
Dave


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## rysskii3 (Apr 19, 2006)

*Re: Rear PCV explained?? (lagamm)*

in the older pcv systems, the breather tube doesnt have the check valve. i was messing around with pcv's and made a conclusion. i have the newest version of pcv (E). it has 2 check valves in it and it also comes with a breather tube that has a check valve. i took the breather tube and started playing with the valve. as soon as i presses on it with some pressure, the vlave broke and came out. so i got the master valve, cut the breather tube check valve out and put the master valve in. the car pulled much harder. but the only concern that i had was that the master valve is made out of plastic and can withstand up top 200 degrees. im looking for similar valve but made out of metal so i can run it in my breather tube. like i said, replacing the check valve made a difference. the car pulled much harder...
so then i took the old breather tube (without the check valve) and put that on with my (E) pcv. that did not work right, the next day i took it off... so dont mix the parts
http://forums.vwvortex.com/zerothread?id=3718903


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## lagamm (Mar 25, 2006)

*Re: Rear PCV explained?? (rysskii3)*

But why have a breather tube with a check valve if the check valve never sees pressure (always under vacuum)
It would explain why it is so flimsy when you put some preesure on it.
I just want to know why I need to upgrade something before I do.


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## rbradleymedmd (Feb 24, 2007)

*Re: Rear PCV explained?? (rbradleymedmd)*


_Quote, originally posted by *rbradleymedmd* »_
Is it detrimental to run a combination of these two systems? Meaning is it bad for the engine to have the Housing w/ 2 check valves and add the breather hose w/ check valve built-in...combine this set-up w/ the Eurojet Front PCV Fix and that gives you a 4-check valve system? Would any problems arise from this set-up?


Anyone with any thoughts on this?


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## Kenestra (Oct 18, 2004)

Seems like all discussions concerning PCV's end with no results or reports back as to what happend. LOL


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## aeproberts21 (Apr 10, 2007)

*Re: (Kenestra)*

I have the same questions. I have a 2006 GTI. I had my VIN number looked up and was told that the new "E" PCV with new gasket is required. They never mentioned the breather tube, but most place I read say that the breather tube is required. I am going to put the EJ fix on as well, but I want to make sure I have this system running correctly. 
The PCV system seems to baffle the forum (and me for sure) since we never seem to get solid answers.


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## Kenestra (Oct 18, 2004)

Is there a way to tell that the rear PCV is bad or going bad? I got underneath the car and checked where the rear breather tube is and also on the DV and it is bone dry, I read that oil residue on the DV means that the rear PCV is going or is bad. Is there any way else to tell?


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## WatchMyDub (Oct 26, 2008)

Kenestra said:


> Is there a way to tell that the rear PCV is bad or going bad? I got underneath the car and checked where the rear breather tube is and also on the DV and it is bone dry, I read that oil residue on the DV means that the rear PCV is going or is bad. Is there any way else to tell?


 Revived, 

I too would like to know more about how to accurately tell if your rear breather valve is toast. 
I was told to check it out soon since Ive been getting a few misfires as well a cat below threshold Code.


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## theblue (Aug 16, 2001)

this all might be related to my problems with lots of smoke when coming to a stop. 

Why don't people run the rear port to a catch can?


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## Krieger (May 5, 2009)

id be thinking turbo seals, not pcv.

the rear port as far as I know is just to allow a source of vac for the pcv system when the manifold on the front is seeing boost.


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## VW_ALEX_MKV (May 15, 2009)

theblue said:


> this all might be related to my problems with lots of smoke when coming to a stop.
> 
> Why don't people run the rear port to a catch can?



I have exactly the same problem! Did you find the problem?? They changed everything on my car. Valve cover, DV, Rear PCV (the new revision), I added the BSH pcv fix, the did a drop down leak test and results were 5%. Compression was A1. I'm out of ideas. I wanted to try a catch can. It happens when the car is hot and is running for a while. So my thoughts were the Crankcase oil vapors were passing through the rear PCV and into the turbo.

Help please. Hope its not the turbo.. Changing the turbo on my car will be a PITA with the dealer that already put a lot of money of this car..

ALex.


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## iGen3 (Mar 21, 2002)

I need to think about this some more also....

I have the early rear pipe. 

I tried running a ProVent in recirc mode from the front, but it always pushed oil out my main seals, and that's never good, so off it came. I think it has to do with the rear pipe. One of these days I need to take it out and see if it has a valve or not.


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## Bunnspeed (Apr 2, 2013)

iGen3 said:


> I need to think about this some more also....
> 
> I have the early rear pipe.
> 
> I tried running a ProVent in recirc mode from the front, but it always pushed oil out my main seals, and that's never good, so off it came. I think it has to do with the rear pipe. One of these days I need to take it out and see if it has a valve or not.


Bump.

I have a K04 swapped GTI and I've been having misfires at WOT above 5500rpm. I've replaced nearly all the hardware that could be the cause of the misfires, switched to Driver Motorsport tuning, etc. with little change. I also have oil leaks on the back of my engine block (fluids don't seem contaminated, already replaced the valve cover gasket) so probably not a head gasket or valve cover gasket issue) and at various other seals. Sounds like crankcase pressure may be too high and causing the oil leaks? 

In any case, could a problem with the rear pcv cause misfires at WOT? Any way to tell for sure that the rear pcv is having problems, or should I proactively remove the check valve?


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## howardc64 (Jul 26, 2013)

*Only way the rear PCV with check valve can make sense*

I've worked on turbo Volvos and have a complete understanding of the PCV path when intake manifold is under vacuum or boost. Its actually very simple and true for all turbo cars. Now working on the friend's 2.0TFSI and trying to understand this rear PCV breather with check valve design.

First, a quick explanation of blow by gasses and why all this vacuum stuff. When cylinder combustion occurs, some gasses will leak past the piston rings. This basically blows air into the crank case and need to be vented to prevent the pressure from pressing out of weak spots like oil seals. Crankcase has open air path to the head so common leak places are oil filler cap, cam seals and rear main seal depending on the different turbo engines. So how do we vent this pressure? On turbo cars, it needs 2 paths

Path 1 is intake manifold when there is vacuum (pistons draws in air creating the vacuum). This vacuum will suck out the blow by pressure into the intake manifold and crankcase/head pressure will become negative or neutral. But what happens when turbo is boosting and pressurizing the air into intake manifold? There is no more vacuum so what do we do?

Path 2 is to vent this pressure to between the air filter and turbo. Usually just before the turbo. There isn't much vacuum here since air filter doesn't restrict much air to create high vacuum. But it is clearly a good place to dump excess blow by pressure.

On 2.0TFSi, path 1 is what is commonly referred to as the front PCV and path 2 is commonly referred to as rear PCV.

Path 1 has a check valve suppose to stop sending pressurized air into the head+crankcase whenever IM is pressurized! The check valve suppose to closes and relies on the path 2. This check valve in path 1 seems to have high failure rate. People use 2 solutions 1) add a stronger check valve (Digital Hippie Mod) or 2) choose to block off path 1 and just rely on path 2 (I think simpler and less failure) Lots of "PCV delete" kits out there for solution #2.

Now ontp path 2. This is NOT a vacuum source. It is mostly a venting source. When turbo pulls in the air, there is plenty of air supplied from the air filter path. No huge vacuum will be created, maybe the tiniest. But you can certainly vent blow by gasses in here without any issue. And when venting, crank case pressure will be slightly positive but not enough to push past any oil seals so its fine. This path has to vent when ever IM is pressurized. Any check valve in this path has to 1) open whenever there is positive pressure coming out the valve cover port for this path 2) probably closes whenever there is vacuum at this port. In any case, this pipe has to be able to blow air towards the turbo intake whenever the port is blowing pressurized air.

In reality, I think path 2 sucking some air back into the crank case from front of the turbo is not an issue. You just want to equalize crank case pressure. If IM suction is so high that it draws air from front of the turbo. Probably not a problem. Volvo turbos I worked on works this way. How much air flow all depends on pipe/hose/inlet sizes rather than check valves.

Furthermore, the air flow rate of path 2 is important. The higher the flow rate, the more blow by gas it can vent and reduce crank case pressure. On Volvo turbo cars, people have up sized path 2 to handle higher crank case pressure as engine got older and rings allowed for more blow by.

Anyhow, this is the only sense I can make of the check valve inside the rear PCV breather (path 2) and which way it opens and closes.

And of course for those who doesn't want to dump oily crank case gas into the intake path, a catch can is installed.

Here is a diagram that helps with understanding. All my comments are in green with green arrows

https://flic.kr/p/R2iGL5

The blue channel around spark plug hole #2 in the valve cover is where blow by gasses will be, this channel is open to the head and also the crank case. Vent path 1 goes to the intake manifold whenever it has vacuum and the high failure check valve should stop the pressure from entering whenever IM is pressurized. Vent path 2 dumps pressure just before the turbo. Any check valve there has to allow the air to flow towards the turbo.

The other problem that affects this PCV air path is the failure of the valve cover internal PCV channels. Seams crack and lots of oil dumps into the pre-turbo air path. My friends car would collect oil at the lowest part of the air path (near the intercooler) and when filled up, gulp it down the intake and a big white puff of smoke. Just a guess but perhaps the alternating vacuum and pressure cycles weakened the glued plastic seams inside the valve cover. Delete path 1 probably makes this system much more consistent and simpler/reliable.


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## kjr6306 (Sep 12, 2007)

Don't understand much about the PCV system, but can a faulty rear check valve be a pathway for boost pressure? I have a low boost issue (P0299) that I have been chasing for months....


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## howardc64 (Jul 26, 2013)

kjr6306 said:


> Don't understand much about the PCV system, but can a faulty rear check valve be a pathway for boost pressure? I have a low boost issue (P0299) that I have been chasing for months....


Looked at the diverter valve? quick google suggest this is the common problem for this code on this engine. Here is how the diverter valve works https://www.eurosporttuning.com/blog/diverter-vs-blow-off-valve/


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## kjr6306 (Sep 12, 2007)

Yes the DV was the first thing I changed. I get a surging at wide open throttle feels like a loss of boost. Other than that, cars drives fine. DTC code is P0299.... I am losing boost somewhere at high RPM. I've had the turbo off and inspected the wastegate, rod and actuator. All of that is solid and looks to be right. Checked vacuum system for leaks....none found. Just curious if an issue with the PVC system can lead to a boost leak?


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## howardc64 (Jul 26, 2013)

kjr6306 said:


> Yes the DV was the first thing I changed. I get a surging at wide open throttle feels like a loss of boost. Other than that, cars drives fine. DTC code is P0299.... I am losing boost somewhere at high RPM. I've had the turbo off and inspected the wastegate, rod and actuator. All of that is solid and looks to be right. Checked vacuum system for leaks....none found. Just curious if an issue with the PVC system can lead to a boost leak?


I think the answer is you CAN lose boost from failing front side PCV. Basically, the front side PCV has has a check valve that is suppose to stop intake manifold from leaking/pressurizing the engine internals whenever boosting. This check valve is high failure item and you will probably lose boost if leaking. Here is a relevant link http://deviantspeed.com/the-ultimate-20t-pcv-fix I believe the author just eliminated the front side PCV.

Below is a paragraph from my previous post that explains this.

A simple test for you is just to install a front side PCV delete kit to eliminate that potential leak path and see what happens to your high RPM boost lost issue. I see kits on ebay for like $20. Pretty simple design.



howardc64 said:


> Path 1 has a check valve suppose to stop sending pressurized air into the head+crankcase whenever IM is pressurized! The check valve suppose to closes and relies on the path 2. This check valve in path 1 seems to have high failure rate. People use 2 solutions 1) add a stronger check valve (Digital Hippie Mod) or 2) choose to block off path 1 and just rely on path 2 (I think simpler and less failure) Lots of "PCV delete" kits out there for solution #2.


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## ROH ECHT (Dec 9, 2010)

Yes...you can lose boost if the "front-side" PCV check valve leaks...you can blow into the intake manifold to PCV tube to check. There is another valve inside the PCV that opens and closes depending on crankcase pressure. This valve directs to the intake manifold under vacuum and to the rear breather tube under boost/pressure. That valve, built into the large diaphragm inside the round disc on the PCV, can also fail and the PCV needs to be removed to test...but if it has failed causing a boost leak, then there is already a problem with the first check valve and you will need to replace the PCV regardless. The check valve inside the rear breather tube, that was originally inside the front PCV just before the route through the valve cover, shuts under vacuum and opens under boost and can also be tested if removed.


Are you diagnosing a boost leak...loss of power...or just getting an understanding of the PCV on the MK5? 

Now, there is another version of PCV out there on some older 2.0t FSI(BPY) having both check valves in the PCV and nothing in the rear breather tube. You don't want to leave the valveless check valve on if you upgrade the PCV to a newer PCV requiring the rear breather with a check valve. This could allow intake air to bypass the turbo and go from the turbo inlet, through the valve cover, and into the intake manifold.


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## kjr6306 (Sep 12, 2007)

Ron, Thanks for your input....always insightful. I have a P0299 DTC code. The DV is good and I have removed the turbo and inspected. All seems fine with it. I clearly have a loss of boost under high RPM's and WOT. The engine surges almost like the waste gate is opening and closing. I did replace the PCV valve with another know good valve. If I am reading your post correctly the PCV valve and the rear check valve part numbers need to be compatible for the system to work correctly....right?


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