Erratic Idle

[Teutonic_Tamer]

No idea then, you know better than me, but it is all the talk over on the 'other' forum about remapped car's PCV valve's failing

So just 'cause someone on another forum got it wrong, but everyone agreed like a following flock of sheep - then that makes it 'correct' then?! 

Which 'other' forum was this?

and what is the best way to upgrade to prevent carbon deposits building up on the valves.   

Ahhhh, that is a completely different issue - but has nothing to do with remaps or turbo boost - or any other similar 'off-tangent' hair-brain ideas!

Presumably the more power you run the more pressure you have in the crankcase? You tell me as i'm not a technician!! 

Pressure in the crankcase has nothing to do with the turbo boost, nor 'power'.  I suggest you go to a library and read some propper textbooks. 

You seem rather belligerent T_T  for someone whom people are asking your expert opinion about something which appears to be your profession? 

Huh - how the fcuk can I be seen as belligerent?  Someone asked a question > someone gave an answer > I disagreed with said answer and gave my detailed opinion > someone disagreed with my opinion > so I told them to do some research in a library. 

Hey ho.  Are you still breast fed, or have you made it to the bottle of formula milk yet? 

I am not a mechanic/technician/workshop monkey so my above suggestions were purely speculative based on a number of GTi owner's having the same problem with a particular component. Far to co-incidental for me.

Maybe an understandable reply to us mere mortal's about exactly why this could be of no relevance to said problem, would be a little more useful to the topic, rather than shoot anyone down in flames on the basis you have a far superior wealth of knowledge!

Sam

But I HAVE given an 'understandable' reply - you disagreed, so I told you to look elsewhere - because it seems that to a few minority on here - no matter what I say, you wont believe me.  So go and buy a text book from an academic bookshop - and not some comic from the newsagent or WHSmiths.

[topher]

i've not taken one from a mk5 to bits (yet ) but surely it needs a vac feed from the inlet mani to function? or have they used a different method to the 1.8T on the fsi engine?

[Teutonic_Tamer]

toph, the clue is in the actual full meaning of 'PCV'   

[sambo]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

Huh - how the fcuk can I be seen as belligerent?  Someone asked a question > someone gave an answer > I disagreed with said answer and gave my detailed opinion > someone disagreed with my opinion > so I told them to do some research in a library. 
Hey ho.

That reply in itself say's it all really 

But I HAVE given an 'understandable' reply - you disagreed, so I told you to look elsewhere - because it seems that to a few minority on here - no matter what I say, you wont believe me.  So go and buy a text book from an academic bookshop - and not some comic from the newsagent or WHSmiths.

Would you care to direct me to said understandable reply, one with a some context would be great

Oh and as for 

Are you still breast fed, or have you made it to the bottle of formula milk yet? 

Still on the good stuff, who ain't?



Sam

[topher]

toph, the clue is in the actual full meaning of 'PCV'   

yeah i know what it is, i had one from an audi s3 in bits in my hands most of today and the pcv check valve is operated by a feed from the inlet manifold.. and pressure in the manifold obviously increases with boost requested from a remap. Just wondered if they worked differently on a mk5!

[Teutonic_Tamer]

toph, the clue is in the actual full meaning of 'PCV'   

yeah i know what it is, i had one from an audi s3 in bits in my hands most of today and the pcv check valve is operated by a feed from the inlet manifold.. and pressure in the manifold obviously increases with boost requested from a remap. Just wondered if they worked differently on a mk5!

All flavours of FSI engines, turbo or not, ONLY use positive pressure in the crankcase.  That earlier comment about the crankcase working on a vacuum is just pure HS, and nearly had me falling from my high chair! 

Yes, you are correct that the actual PCV works from the 'inlet manifold', but technically, it is just a pressure 'difference', rather than an out and out vacuum.  Because FSI engines generally don't have much of a manifold vacuum, by simple virtue that FSI engines are not 'throttled' in the traditional sense.  That is why FSI engines now use a vacuum pump for the brake servo, just like oil burners. 

[topher]

yeah it doesn't need much vac to open the check valve.. but under boost when its closed, is that not where the valve fails? in a similar fashion to the old plastic diaphragms on the dv's?

i wouldn't need to be asking these questions if i could get my etka working again and could see how it all went together

[Teutonic_Tamer]

yeah it doesn't need much vac to open the check valve..

Which valve?  There are actually two valves in the PCV unit, one small one which just acts as a bypass for the cyclonesm and the larger diaphragm valve.  And there is also a piston in it too, which is operated by pressure, not vac.

but under boost when its closed, is that not where the valve fails? in a similar fashion to the old plastic diaphragms on the dv's?

No, because dispite what the 'big boost numbers boys' will tell you, in the inlet manifold, there isn't actually that much pressure - if there was, engines wouldn't pass emisssions tests, because the charged volume in the combustion chamber would just be pushed out the exhaust valves during the valve overlap phase.  (I think?  It's getting late, and I'm feeling decidedly dodgy - so I might be talking BS too!)

i wouldn't need to be asking these questions if i could get my etka working again and could see how it all went together

Look in the Mk5 maint + info section, and download the 'self study guide' for the GTI engine - it details how the PCV works. 

[topher]

i'd rather just get my hands dirty and investigate it for myself by taking one to bits

can i borrow your car?

[ukdub]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

The PCV valve has NOTHING to do with turbo boost!    It is ONLY the DV which is affected by turbo boost, unless you have modified your engine to work on the two stroke cycle!

The PCV valve may have nothing to do with boost,  but it can be affected by it.  Therefore increased boost can damage it.

Crankcase Ventilation

The crankcase is maintained in a constant
vacuum while the engine is running.
The crankcase breather that supplies
this vacuum is connected to the intake
manifold.
The crankcase blow-by gases are separated
in two stages. In the first stage, the
primary oil separator in the oil filter module
takes most of the oil out of the gases. A
second separator in the cylinder head cover
removes the remainder of the oil from the
gases.
Since a turbo engine requires a more
sophisticated pressure control system, a
two-stage pressure control valve is located
on the cylinder head cover. If vacuum exists
in the intake manifold, blow-by gases flow
directly into the intake manifold.
If a boost pressure is present in the intake
manifold, a one-way valve in the pressure
control valve housing closes and the blowby
gases flow into the cylinder head cover
ahead of the turbocharger. The system can
detect faulty installation of the pressure
control valve. Unmetered air is detected by
the reaction of the oxygen sensor.

Where - exactly did that blatant cut, copy and paste come from?  Because that categorically is NOT from a Volkswagen Group FSI engine?  And there are some serious, and fundamental basic errors with that!

And I will categorically state again, boost pressure has absolutely NOTHING to do with the PCV - nothing!  Furthermore, it can NOT be affected by boost either.

But hey, you read and stole the above from some other internet forum, so that then means it must be true! 

Didnt say it wasnt a copy and paste.

It was copied and pasted from the 'self study guide' for the GTI engine

Have you read it

Plus YOU got that guide from from the SAME internet forum as I did so it must be true.

Page 8 I think you will find. 

Still stand by your
Because that categorically is NOT from a Volkswagen Group FSI engine?  And there are some serious, and fundamental basic errors with that!

http://www.golfmkv.com/forums/golfgoodies/mk5golfengine.pdf - Self-Study Programme