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Discussion Starter #1 (Edited)
This tutorial is marginally related to my other tutorial just posted about valve cover gasket replacement. It makes sense to carry out this one (or at least check the valve) if you're doing the former, but can also be done separately.

What is a PCV valve?

The valve cover of the BPD/BPE engines has the positive crankcase ventilation (PCV) valve integrated right into the cover. The function of this unit (ie. that of the PCV valve) is to allow any extra pressure (resulting from blow-by) building up under the valve cover to escape from it.

This extra gas, which might also contain diesel/oil fumes, is routed back through a relatively thin hose (detailed in step 3 of the previous section) into the intake path, right after the MAF, but before the turbo, gets sucked into the engine again and hopefully gets burnt there.

For this to work correctly there has to be a valve involved, which will only allow the extra pressure and gases to escape, but not allow fresh air (or the previously expelled gases) get sucked in. This is what the PCV valve is doing.

The valve diaphragm

The valve works by having a rubber membrane in it, which on one side has the outside atmospheric pressure pushing against it, and on the other side the pressure of the crankcase. Depending on which pressure is higher, the membrane is pushed in one or in another (opposing) direction and closes or opens a hole through which gases can flow between the valve cover and the intake.

This ensures that if the pressure in the crankcase is lower than the outside atmospheric pressure, and thus air would rush into the crankcase through the pipe, this does not actually happen, because the valve closes. However, when the relation between the pressures reverses, and there is a higher pressure inside the crankcase then outside of it, that extra pressure (actually, the gases causing it) can escape through the ventilation pipe.

How the PCV valve fails

The PCV valve usually fails when the diaphragm in it gets torn, because then it can’t separate the inside and outside pressure areas from each other anymore and won’t move depending on which pressure is higher. Also air and gasses will be able to freely move in both directions through the diaphragm itself, which – depending on the construction of the valve – will allow crankcase gasses to possibly escape right through the valve, and allow fresh air to get sucked into the crankcase, leading to all kinds of problems with the fuel mixture and the metering of different intake gasses.

The solution to this problem is to replace the torn diaphragm with an in-tact one, which will restore the proper functioning of the valve. Unfortunately, most of these valves and especially the valve cover is not designed in a way that would make it easy to replace the membrane. Still, it’s doable, and allows you to save quite a few bucks, because eliminating the need of having to buy a whole new valve, or in this case, a whole new valve cover assembly, for several hundreds of bucks.

The repair

Tools needed

There’s really only one kind of tool you’ll need to replace the valve diaphragm:
  • several picker tools (at least 3 of them)
Parts needed

Again, you will only need one part to fix a torn diaphragm:
  • a new PCV diaphragm

Unfortunately, not only is the PCV diaphragm not sold separately by VW, but it doesn’t seem to be available through “official” aftermarket OE channels either. I got mine off eBay, and I’m not aware of there being any other source for it.


Replacing the PCV valve diaphragm can be done either in-situ, with the valve cover still on the cylinder head, or when the valve cover has been removed. The latter is preferable, because for one it allows you to inspect the valve cover in more detail, and to look for possible cracks or other damage on (or even inside of) it, which will obviously have the same effect as a torn PCV valve diaphragm, and make replacing the latter futile. It will also grant you access to the PCV valve itself from all angles, which will make disassembly a lot easier and safer. You’ll also not risk losing any parts or tools into the engine compartment.

  1. In order to replace the diaphragm you will need to somehow pry off the cover cap of the PCV valve, that’s fastened onto the valve cover and is hiding the diaphragm and the valve mechanism. The cover is fastened using not less than 8 (!) separate clips, which are all very stubborn. What you’ll need to do is to bend these clips away from the protruding “claws” that go into them, and then lift the PCV valve cover cap off.


    However, because of the clips being so close to each other and being very tight you’ll not be able to do this one-by-one, but you’ll somehow try to bend at least 3 off them at once in order to move the cover just a little bit off on that side. Then when you’ve done that, you can go to the next 3 clips and do the same, gradually lifting more and more sides/parts of the cover cap, until you go fully around, and can remove it.

    I found that the best way to do that was to leave one of the picker tools under each of the 3 clips (not depicted in photos), which would keep them pushed away from the housing with the claws and then allow me to lift/pry the cover a tiny bit off/upward on that side. (If you pry less than 3 clips at once, you’ll not be able to lift the cover, not even a tiny bit.) The rocker cover itself seems to be reinforced under the clips, but if you’re worried you can also put a piece of thin metal there in order to distribute the force on a large surface and help avoid cracking the cover.

    Also be very careful with prying the clips themselves, because if you bend them too much, they might just break off, which will be fatal for the valve and make the repair impossible. And try all this in decently warm temperatures, not in the cold, which again, would make the cover plastic brittle and easier to crack accidentally.

  2. Once you’ve successfully pried off the cover cap from the PCV valve, carefully lift it off to expose the diaphragm and the inside of the valve mechanism!


    Make sure you do that indeed carefully, because there’s a metal spring inside the valve, which you don’t want to loose!


    If you lift off the diaphragm you can finally see the inside of the valve and how it works:


  3. Now you can replace the diaphragm. Note the yellow plastic piece at the center of the diaphragm, which at first sight seems to be integral part of it and glued onto it, but actually isn’t. You need to transfer that to your new diaphragm after you pulled it off the old one.


    The valve might possibly work also without this plastic piece, but it will definitely wear out sooner, because the metal spring will rub directly on the rubber diaphragm.

  4. Now you can reassemble the PCV valve by putting in the new membrane and putting back the cover cap over it. Make sure you put back the new diaphragm with the right orientation, meaning with the portruding piece and the yellow plastic part pointing down, and going right into the center of the metal spring. Then carefully put back the cover while making sure the the diaphragm stays centered inside of it and over the hole of the valve.

  5. Once you put the PCV valve cover cap back and the claws start to catch into the clips, you’ve to go around the cap and push at each clip position down with medium to heavy force until you actually hear them „click in”. You should also visually inspect each clip to make sure that they’re all engaged properly. If any one of them don’t, the valve might pull in false air and not work properly.


    If the cover cap is sitting tight on the PCV valve with all clips engaged, you’ve finished the replacement. If you’ve done this all in-situ with the rocker cover on the cylinder head, you are finished – and if you’ve done this while the rocker cover was removed, you can proceed with its reinstallation onto the cylinder head.

Note: Obviously the rocker cover most likely has a second valve/diaphragm under the larger cover cap, too. However, because I found no replacement diaphragm for that one (not even on eBay), I didn’t bother prying that one off, because all I could possibly achieve was breaking the cap and make things even worse than they are now. And because I had no indication there was something wrong with the valve in the first place.

Actually, the diaphragm I’ve replaced also seemed fine, but because I already bought the new part, I just went ahead and replaced it anyway (because I obviously had no use for the new one otherwise). Interestingly enough my engine seems to idle smoother now, but I’m not really positive that this is in any way related to or the result of the PCV diaphragm having been replaced, and if anything, might have to do with the cleaning of the valve cover (ie. the rocker cover) itself and the replacement of the valve cover gasket.

Anyway, if somebody comes across a damaged valve cover that he can take apart or just wants to see what’s under that larger cover cap, I’d be happy if he could let us know and send some pictures of what he found there. If there’s also a diaphragm and he could take measurements of it, that would be even better, because then we could possibly try and look for a replacement diaphragm.

1,086 Posts
Discussion Starter #2
Leaving these measurements here for future reference, for the case that the original product becomes unavailable, and/or somebody will need to look for a replacement with a matching size:


Full outer diameter seems to be 53mm, the diameter of the actual valve part (where the yellow plastic part goes on/around) 14mm. Of course because the diaphragm is made of rubber the measurements might not be fully accurate.
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