Crankcase Ventilation Flow Diagram

[UrS4boy]

Revised ABY Crankcase Ventilation Diagram

? geez yes the N80 is on the tee pipe that goes into the back of the inlet manifold so it can vent fumes to be burnt under combustion, it never sees boost as that's where the 1 way valve is on the ABY

Thanks Jamo, Newsh and A80Avant. Not having an actual ABY to run out and look at is a disadvantage. Thanks for your help. I *think* this next revision has it sorted (let me know). I added flow from the N80 Evaporative Emissions Valve *TO* the "tee" hose connection. (I am pretty sure the ECU closes the N80 when the engine is under boost so the bleeder valve being closed doesn't really come into play). I would still like to see a photo of where the inlet to the underside of the ABY/ADU/3B intake manifold takes place. See attached for the current revisions:

[Jonas_R]

Your assumption about the N80 valve is correct. The ball valve (one way valve) is located so it does not have any effect on the N80 valve.

[ChrisAudi80]

I think one of the problems in this discussion is the over/mis-use of the term "PCV" to describe the two valves involved. As per VAG, they are called "bleeder valve" and "pressure regulating valve".

The bleeder valve is a one way ball valve. Under vacuum the ball is sucked upwards, out of its seat (but still contained in its "cage"). This allows the oil vapours and blow-by from the crankcase to be drawn into the intake manifold under intake vacuum.



In normally aspirated engines, that is the end of it. However, our 20Vts are different in that the crankcase and cam cover still need to be ventilated, even when the intake manifold is under boost pressure. This where the pressure regulating valve comes into play.


It contains a spring-loaded diaphragm. Under vacuum, when the bleeder valve is open, the pressure control valve is CLOSED with the spring pushing the diaphragm against an orifice. When the intake manifold is put under pressure (boost), the bleeder valve ball is pushed against its seat, closing that path for the blow-by and oil vapours. All is not lost since, at the same time, the pressure control valve is opened by the vacuum created by the higher flow going to the turbo AFTER the MAF, pulling on the diaphragm, against the spring pressure, lifting the diaphragm off the orifice, allowing the vapour and blow-by to be draw in to the unpressurized flow from the MAF to the turbo inlet.

When you let your foot off the accelerator pedal, the throttle plate shuts, creating a high vacuum situation. At that point the pressure control valve again closes under its spring pressure and the bleeder valve ball is lifted off its seat and opens.

I don't think I can explain it any better without creating more diagrams.

I am still trying to get my head around how the Pressure Regulating Valve (PRV), p/n 034129101B just to be clear, operates.

I have looked the diagrams again and again. Last night I changed around the install of the PRV. It was connected wrong according to the AAN ETKA and the other AAN diagram. I have the 034 catch can system on the S6 and have always wondered why it has always been dry. Turns out until a few weeks ago one end of the hose from PRV to can was not connected. Whole other story.

It was a PITA to change it around because of the position of this infamous PRV and I had to change one of the clamps. Which I dropped but got out.

I looked at the valve and it is quite clean inside, bought a new one a few years ago, and I can blow through it in both directions. The spring holds the diaphragm up against the head part. I just don't understand this valve.

I would say that it would have to be closed during idle/light throttle, but it is not.
I no understand. I understand the check valve under the IM.

My idle has been erratic since reconnecting the hose to the PRV. Especially when AC is on. When engine is hot and I shift from N to D and tip in lightly, the engine almost stalls and sometimes does. The RPM really dips. If AC is not on, no issue.
I have cleaned the ISV. The T hose which sit on top of the check valve is OK.

Will test today how it runs with the PRV connected correctly.

[UrS4boy]

C4 UrS 20VT Crankcase Ventilation System Info

Have a read through the full PCV info at this link (click on the link and then on the words "Crankcase Ventilation" in the box in the lower right corner:

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

[ChrisAudi80]

I have. Several times. Still don't understand how the valve operates.

Why can I blow through this valve in both connections? It is open bi-directionally unconnected (1bar absolute)

[UrS4boy]

What part of "closed under engine vacuum" don't you understand? Sounds like the valve you are testing is busted/ broken/ borked/ kaput/ dood/ tot/ guasto/ 死んだ/ νεκρός/ inoperante/ мертво/ muerto/ gone to meet its maker.

[Pirvu Eugen]

I have. Several times. Still don't understand how the valve operates.

Why can I blow through this valve in both connections? It is open bi-directionally unconnected (1bar absolute)

look here.. http://www.sjmautotechnik.com/troubl...oost.html#hose

[ChrisAudi80]

look here.. http://www.sjmautotechnik.com/troubl...oost.html#hose

Thanks. I looked at sjm a while ago about this, but forgot about it. This explanation is slightly clearer. So, there is always some flow though, but under enough vacuum it closes partially.

Dave, thanks for your input. I will check in a moment if it is borked.

[ChrisAudi80]

PRV is not borked. Changing it around to correct connection made all the difference.
Idle with AC on is way better.

I was not the one that put the PRV in the wrong way around.

[UrS4boy]

Thanks. I looked at sjm a while ago about this, but forgot about it. This explanation is slightly clearer. So, there is always some flow though, but under enough vacuum it closes partially. Dave, thanks for your input. I will check in a moment if it is borked.

I probably need to update my post with the info from the SJM site. Re-reading one of your posts, I think the problem was you were testing by blowing, not sucking. (There is a joke there but I will let it pass).

[ChrisAudi80]

I probably need to update my post with the info from the SJM site. Re-reading one of your posts, I think the problem was you were testing by blowing, not sucking. (There is a joke there but I will let it pass).

Sucking and swallowing is not my thing. Especially not hot man ...errr.. 20W50 oil

[vertigone]

Hi guys,
need a litle support about all this things
A hose on my 3B was cracked
so I decide to buy this from 034 :


But here is what I find in ETKA about 3B :


Seems to be 2 different system :
Mine was the bottom one (with little hose connexion to cam cover #13)
034 hose seems matching the upper system WITHOUT the little hose to the back of the cam cover

I have installed 034 hose but of course need to "blank" the little pipe on the cam cover with a screw.

What is the purpose of this little hose on the back on the cam cover on 3B motor ?
Why ABY/ADU motors don't have it ?
What kind of problem can I have ?

many thanks for you help.

[UrS4boy]

What is the purpose of this little hose on the back on the cam cover on 3B motor ? Why ABY/ADU motors don't have it ? What kind of problem can I have ? many thanks for you help.

The 3B, AAN, ABY and ADU all have a vent to help remove oil vapours from the underside of the cam cover. The ABY vent it larger than the 3B (AFAIK). This plumbing is shown in pink in this diagram:

[newsh]

What about parts 1A and 4A? What have you done with them?

[UrS4boy]

What about parts 1A and 4A? What have you done with them?

"4A" is No. 3 in my diagram, the pressure regulating valve.