pcv after maf?

Matt82

Matt82

Matt82

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13 Mar 2004
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just got a question about the location where the pcv system reconnects to the intake.

on the various engines i can remember the layout of, it appears it would connect anywhere there is vacuum. i cant see that why the system wouldnt work, as long as there is vacuum

the reason i ask is my golf 1.8t doesnt have a catch tank of any sort so any mist/crud ends up straight back in the intake and blown into the engine

ive done a lot of monitoring and i notice i get most knock detected on cyl 3 and 4.

my theory is that this is due to carbon build up. more specifcally, crap from the pcv blown back into the engine and due to the extra mass it is carried further and ends up in cyl 3 and 4

therefore. i want to inspect cyl 3 and 4, decoke if necessary.

then why cant i redirect the pcv to the start of the airbox, ie before the air filter, so that any mist/crud gets caught by the filter, cyl 3-4 stay clean and i can make more power
 
The PCV has a nipple (immature giggle) on the intake manifold itself. It's typically on the underneath towards the middle. Needless to say this puts it way after the turbo.

As far as I remember you can actually scrap the PCV altogether but it's sensible to put a catch can in to replace it. A few guys on Audi-Sport forums have done this, might be worth asking over there?
 
vacuumdiagramug9.jpg


I hate the vac layout on the 1.8T it sucks, yes you can ditch the PCV system but i wouldn't, i also wouldn't route to the intake pre filter, due to it getting covered in oil quite quickly.
 
A PCV valve requires vacuum to operate it - if you plumb it in at the airbox it will never see any vacuum so it won't work.

You could dispense with the valve altogether and vent the crankcase into the airbox like early carbed engines used to do, but this is then relying on crankcase pressure to blow the fumes out, rather than manifold vacuum creating a lower than atmospheric pressure in the crankcase. This will give significantly worse oil control and you risk contaminating the air filter and MAF sensor. I wouldn't recommend it.

Oil mist will lower the octane of the inlet charge anyway, so can cause detonation without there having to be a build up of carbon. However, if oil mist is causing this sort of problem then either your engine is running on the ragged edge (i.e. CR, boost or inlet temps too high) or the engine is damaged or just plain worn out.
 
even if there is the oil filter between pcv and maf??

LSP3. i have already ditched that.

dog breath, why wouldnt there be a vacuum in the airbox? there is a 1.8 litre engine and a blower suckign on the airbox
 
For the love of God don't put your oil breather before your MAF, that'd be a pretty 'special' thing to do.

The air filter won't catch all of the tiny droplets of oil, and you'd end up on first name terms with your local parts counter with the amount of MAFs you'd destroy.

A MAF is a massively sensitive bit of kit, and will not appreciate being blasted with oil vapour :p
 
Matt82 said:
even if there is the oil filter between pcv and maf??

LSP3. i have already ditched that.

dog breath, why wouldnt there be a vacuum in the airbox? there is a 1.8 litre engine and a blower suckign on the airbox
Click to expand...

that filter wont stop it all and will block up fairly quickly anyway
the only thing in front of the maf should be the airfilter, even a clean oiled K&N can give problems with oiling up a maf
 
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Firestar_3x said:
Wrong side of the turbo.
Click to expand...

airbox is before the turbo, of course there will be a vacuum there

as for the mist vs air filter vs maf.... god knows.

i can see the logic that the maf wont be happy. maybe another foam filter could be put in place at the end of the pcv before it goes to the airbox.

long and short of it is... install another catch tank. still no promise that oil wont get in (even if its baffled) and they have to be emptied which is agro


as for knock detection and the fuel rail... ive seen it on practically every 1.8t ive worked ont hat most knock occurs on cyl 3 and 4 and the first logical reason i can think is piston deposits.
 
Current system works on a feed from the intake manifold which goes through a splitter then into the crank case which exits into the non presurised air intake side of the turbo after the MAF via a one way diaphragm valve.

You either need to remove the lot and fit one of those stupid halfords crank case filters, or forget about it.

If 3 & 4 are last on the fuel rail they stand a chance of getting less fuel, whats the odds of all 1.8t's having deposit buildups?
 
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