Positive Crank Ventilation (PCV) is important to the engine to ensure that any pressure that is built up in the crankcase during combustion is released, this use to vent to atmosphere and thus cause additional smog problems associated with car use. Modern cars deal with the problem of venting to the atmosphere by passing the gas back into the air intake, this allows the un-burnt hydrocarbons to have another go at being combusted and are now set up to actually vent the system by use of a vacuum.
The PCV Valve works to use inlet manifold vacuum to regulate the flow as is needed.
Definition of a PCV and the valve and a bit more info.
On the 20vT engine ventilation is done via an exit on the top of the engine right side and undernearth the inlet manifold in the front center for the engine. The vacuum source comes from the middle of the inlet manifold. the pipes are a combination of formed plastics and rubbers or in some cases metal pipes. The valve changes the flow of gases depending on the action of the inlet manifold.
The problem with the system is that over time the oil that is in the gases starts to corrode the pipes and thus causes leaks, in the case of a lot of MK IV this is usually visible by the top pipes becoming torn and releasing gases that can be smelt in the car.
On this set up, the pipe highlighted is a single one off piece that can be re-fabricated without buying the OEM part but it is harder to make due to the angle, buying the original will just cause the same problem again in a few years. A lot of people therefore seek to make their own alternatives which was what I wanted to do, so I bought a T-Pieces and made my own set up however I quickly realised that the pipe going down to the lower crankcase was made of plastic and this breaks, in loads of places.
So I found a metal alternative off of another VAG system, this allows two separate tubes to the top crankcase breather and the other back into the intake.
As the picture above shows the metal pipe in the center of the picture connects to a three way rubber T-piece, to the top goes a thin tube to the inlet manifold for the vacuum, to the right goes a thick tube to the lower crankcase. The three way T-pieces holds the magic PCV Valve, it is a separate part that is housed in thick part of the tube and in this picture held with a jubilee clip.
The valve can get bunged up and all the other parts can split or get damaged so for the sake of this document lets assume that in one day I decided to replace and modify all of the parts discussed rather than chase this damn problem for over 9 months before properly fixing it.
I ordered:
The lower crankcase pipe,
The o-ring that goes with it
The rubber t-piece,
The PCV Valve,
The hose that goes to the manifold,
The metal pipe that goes up to the top
A lot of silicon pipes
New dipstick tube incase you break the old one, if it is old you will break it if you don't have a spare.
The work:
Undo the plate infront of the inlet manifold, this require the two nuts that hold the return pipe for the secondary air system to be undone and two allen bolts that hold the plate to the manifold. I will post more information about the removal of this plate
hereIn the above picture the plate is lose and ready to be removed.
In the above picture, the plate has been moved and you can see the pipe going from the inlet manifold to the rubber t-piece that holds the PCV valve.
Another view that shows the larger pipe for the bottom crankcase breather.
With the manifold vacuum tube removed you can see the PCV Valve, it is the white part in the t-piece. This also gives you a better view of how to remove the lower crankcase breather, there is a retaining clip that needs to be pulled out, the whole pipe actually seats on an o-ring that should be replaced as well.
Here is a picture of the new vacuum that connects to the PCV valve.
This can all be made up out of the car before you put it in and it really does make it easier.
The metal tube however is hard to alinge so I put that in and up to the top crankcase hole, then fitted it up to the other pipes under the manifold. Here is a little video to show how it was put together:
PCV pipes Video
After a little jiggerling I was able to seat the metal pipe close to the engine and therefore make a clean set up. I need a 90 degree elbow silicon pipe for the top engine breather but other than that it all went back together and now looks like this.
After the first trial set up, my engine light went out on it's own and now I have no boost leak issues and it runs much better. I will add that I am replacing all vacuum pipes with silicon as I go so there might be other factors.
Part numbers:
The lower crankcase pipe - 06A-103-213-F
Clip for lower crankcase pipe - 037-121-142-A
The o-ring that goes with it - N-904-673-01
The rubber t-piece - 06A-103-247
The PCV Valve - 035-103-245-A
The hose that goes to the manifold - 06A-103-221-AF
The metal pipe that goes up to the top 06A-103-213-S (From older 1.8T AWR etc).
A lot of silicon pipes
New dipstick tube incase you break the old one, if it is old you will break it if you don't have a spare 06A-103-663B-SJ.
References or sites to read more:
A part source but also a catch can idea
Audi source where I found some part numbers
Loads of information