# Faulty PCV Valve - A Cautionary Tale



## steveupton (Mar 23, 2010)

Sorry for this lengthy tale and particularly to those members who are already clued up on this but thought it might be of use to other members who have experienced similar problems without knowing the cause.

The Positive Crankcase Ventilation Valve is a very cheap part, cost about £7 from Audi, but if it stops closing when it should, it can cause all sorts of problems as I recently discovered.

It all started out when I noticed that the cam chain tensioner started to rattle on start up, so I dropped the sump to check for debris on the oil pump pickup strainer and found nothing - clean as a whistle. Next I suspected that the non-return valve in the oil filter housing was not working and allowing oil to drain back into the sump, replacing this - pig of a job - solved nothing. An oil pressure check showed pressure was good, so was thinking may be the cam chain tensioner itself needed replacing and was steeling myself for an expensive repair job. Also, the new injector seals I had fitted last year were weeping again.

Last week, I thought it's about time I got round to replacing the PCV valve as I had a replacement that had been sitting in the garage for several months, what had put me off doing it was that one of the silly Audi single use clips had been fitted with the crimp part in the wrong place to get a screwdriver in to release it. Eventually managed to cut it off with my dremel and replaced the PCV valve, I also fitted another set of injector seals.

1 week on and the engine is now totally silent on startup in the morning and I can only think that because the old PCV valve was not closing properly, excess pressure build up under the valve cover was preventing oil from getting there on startup and probably causing the injector seals to leak.

I really only have myself to blame because Morgan at Vagcheck did tell me last year that he thought it might need replacing and there was a post some time ago, that I can't find now, explaining that injector seal leaks can often be attributed to this fault.

Needless to say, this is an item that will be very high on my preventative maintenance check list now.


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## nordic (Apr 26, 2010)

Glad you've sorted it 
Question, was it stuck open or closed?
I've noticed it is such a poor quality part, that it never seals fully, allowing pressure to slowly go into crankcase. However crankcase and top end are connected quite well, pressure shouldn't differ from each other...

Although I don't have PCV valve anymore - all goes directly into oil catch tank now.

Thanks!


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## steveupton (Mar 23, 2010)

nordic said:


> Glad you've sorted it
> Question, was it stuck open or closed?
> I've noticed it is such a poor quality part, that it never seals fully, allowing pressure to slowly go into crankcase. However crankcase and top end are connected quite well, pressure shouldn't differ from each other...
> 
> ...


Was sticking open intermittently, checked it with compressed air. Noise from cam chain tensioner was only on cold start at low ambient temperature for about a second and even then not every time, so presume once pressures equalised oil could circulate properly.

Which oil catch tank kit have you got because was looking at the Forge kit but believe this retains PCV or if you fabricated it, would you mind posting up the plumbing diagram please.


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## nordic (Apr 26, 2010)

I see... PCV system on these engines is well designed, except that all suffer from oil excess in the intake. Oil fumes not only lower octane of the fuel, but also deposits where it shouldn't.

Adding catch tank makes system less efficient, but gets rid of oil nicely. I'm quite sure there are many oil catch setups, mine is rather simple.

I've got forge oil catch tank from ebay, for a fraction of what they cost - they do cost a leg or two! But they do the job it seems.

Engine has two breathing points, one at the bottom and one at top, I've just connected them together and routed into the catch tank. Then routed clean catch can's output into preturbo hose, just where the hockey puck (PRV valve) connects, instead of it. So there is no PCV nor PRV valves anymore. The PCV connection to manifold is blocked.

The drawback of this approach, is that crankcase gases are no longer being sucked out (as per original design), but rather push themselves through the catch tank. It does compromise the ventilation a bit and system needs checking that it is not getting blocked or tank needs draining now and then, but since I change oil precisely every 6K, there should be no problem.

All hoses, T or angle joints are 19mm in diameter.

Kind regards


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## Jurpo (Jun 24, 2009)

034 Motorsport makes metal replacement valve.
Ought to be better.
http://www.034motorsport.com/engine...-21834.html?osCsid=69q4n8ur9mg3emadsjkr76imn5


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## steveupton (Mar 23, 2010)

Thanks Nordic for a very comprehensive answer, food for thought I might just go this route when time allows.

Thanks Jurpo, that looks much better than the poor quality Audi item, think I will invest in one of those for the short term at least


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## steveupton (Mar 23, 2010)

Jurpo said:


> 034 Motorsport makes metal replacement valve.
> Ought to be better.
> http://www.034motorsport.com/engine...-21834.html?osCsid=69q4n8ur9mg3emadsjkr76imn5


Just went to order one of these and minimum shipping cost is $60!! Is it available from another supplier in the UK?


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## shaneh (Apr 4, 2011)

steveupton said:


> Jurpo said:
> 
> 
> > 034 Motorsport makes metal replacement valve.
> ...


I'm pretty sure it's possible to get hold of a replacement so long as it's just a check valve :?

I'll check at work tomorrow and post back here if i can get them and see if anyone is interested.

Is much pressure put through this?


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## steveupton (Mar 23, 2010)

Pretty sure it is just a check valve but don't know what pressure is in the crankcase, will try and find out.


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## shaneh (Apr 4, 2011)

I can't see it being much, but it would have to overcome the spring pressure in the check valve.

A rough figure would be great mate.


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## ricer (Dec 4, 2010)

How hard is this to replace? anyone got a how to?


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## nordic (Apr 26, 2010)

Just to clarify, crankcase pressure doesn't have to over come spring tension. Spring there is just to keep the blocking plate under tension. This PCV valve is open (spring compressed) only when there is a vacuum in manifold, sucks crankcase fumes into combustion. So at worst, the tension must be weak enough for vacuum to be able to open the valve. During boost PCV valve should be sealed tight and crankcase gases travel to preturbo side via PRV valve (hockey puck).

The quality of PCV valve is such, that it never seals and boost leaks into crankcase, but not much. It may also be done purposely to help gases to escape by replacing them with fresh air... Just a thought.

Kind regards


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## steveupton (Mar 23, 2010)

ricer said:


> How hard is this to replace? anyone got a how to?


It really depends upon how the single use clips fitted by Audi are situated, if the crimp piece is visible on both clips, it isn't too bad as you can get a screwdriver in and by forcibly levering from side to side, the clip will open up and with some long nosed pliers, you can then remove them. The problem I had was that the larger of the 2 clips had the crimp piece in a place that was not visible and I had to cut through it with a dremel very carefully so as not to damage the breather hose.

It's located underneath the inlet manifold on the right hand side (looking from the front) and is hidden inside a breather hose that is connected to another T shaped hose.


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## steveupton (Mar 23, 2010)

nordic said:


> Just to clarify, crankcase pressure doesn't have to over come spring tension. Spring there is just to keep the blocking plate under tension. This PCV valve is open (spring compressed) only when there is a vacuum in manifold, sucks crankcase fumes into combustion. So at worst, the tension must be weak enough for vacuum to be able to open the valve. During boost PCV valve should be sealed tight and crankcase gases travel to preturbo side via PRV valve (hockey puck).
> 
> The quality of PCV valve is such, that it never seals and boost leaks into crankcase, but not much. It may also be done purposely to help gases to escape by replacing them with fresh air... Just a thought.
> 
> Kind regards


Thanks very much nordic for a very good explanation of how it works and I think I'm going to copy your catch tank installation to get rid of it along with the PRV valve.


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## GroverUK (Dec 2, 2010)

I belive Andy (yellow-tt) is selling a forge catch tank. Think he said it had never been used and wanted less than the rrp.


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## steveupton (Mar 23, 2010)

GroverUK said:


> I belive Andy (yellow-tt) is selling a forge catch tank. Think he said it had never been used and wanted less than the rrp.


Thanks GroverUK, will contact Andy.


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## Johnclem88 (Aug 22, 2011)

nordic said:


> I see... PCV system on these engines is well designed, except that all suffer from oil excess in the intake. Oil fumes not only lower octane of the fuel, but also deposits where it shouldn't.
> 
> Adding catch tank makes system less efficient, but gets rid of oil nicely. I'm quite sure there are many oil catch setups, mine is rather simple.
> 
> ...


Sorry to bring this topic up again.

But does this mean all I will need is a long length of 19mm hose? and run one length from the outlet at the bottom underneath the inlet (I think there is a 90 degree hose there as standard (BAM)?) and then one from the rocker cover?

Thanks

John


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