Do I have this PCV thing down?

Ok the PCV valve opens (not sure when) and vent's to the intake manifold, right? And the breather hose vents to the intake hose after the MAF. What discerns what goes through the PCV valve and what goes through the breather hose when the PCV valve is open? I'm buring a lot of oil and have siginifacnt turbo lag (due to I think some boost leaks). I know a bad PCV valve will cause extra oil to be blown out the oil cap/dipstick and breather hose, but is that also considered a boost leak?

I talked to a couple of techs here and they said that (at least on most German cars) the breather hose is sourced from a specific location via channels in the VC.

 

[Bimmubishi]

Good post. I think that the breather's always open wheras the PCV valve is vac operated. Since they're both on the valvecover, i have no idea when one works and one doesn't. If you have oil coming out, the seal on the cap could be bad, the rings could be bad on your pistons too. Is your dipstick blowing out?

 

[Ian M]

The PCV is supposed to be closed during WOT boost/heavy load,and idle conditions.

Its basically a one-way check valve. Under light cruising,when theres no vaccum present,the ball inside will drop into into a cavity and allow air to pass. Thats the rattle you hear when you shake a PCV valve.

Once vaccum is present (idle),the ball should be pulled up onto its seat,blocking air passage. If theres a backfire (or boost in our case),the ball will go to the other side of the cavity and seal the other end.

 

Quote from Bimmubishi:"I think that the breather's always open wheras the PCV valve is vac operated." the term "PCV" stands for Possitive Crankcase Ventilation, so when the preasure in the crankcase become possitive it blows out of the pcv valve and when it becomes negetive it sucks the pcv valve shut so it can suck FILTERED air through the breather hose. so yah you hit it on the nose.

 

[spoulson]

Any air going in through the breather or PCV are both filtered. So what is the difference between air going in/out the PCV versus breather? i.e. if the PCV is broken or clogged, why does it cause problems when the breather is open all the time?

 

[RayH]

I think the problem is if the pcv valve is not working, intake pressure under boost will leak into the the valve cover pressurizing it. This dissipates through the breather and possibly causing enough pressure to push the dipstick out? So a bad pcv valve ends up being a boost leak.

 

[spoulson]

Is it reasonable to reloate the PCV hose to a non-pressurized source, such as where the breather hose goes before the turbo?

 

quote:Originally posted by Bimmubishi:
Is your dipstick blowing out? My dipstick used to blow out, so I put a little duct tape around the worn rubber where it seals, and that fixed it. But I was still using a ton of oil. So I checked the PCV valve and it rattled, but didn't seem to seal, so I replaced it. That was yesterday so I don't know what effect it will have on my oil consuption problem yet. I think my rings are probably worn so thats more than likely where most of my oils going. I have a JDM motor with only about 10k on top of what ever it had to begin with, and didn't rebuild it, so that's a factor. But it didn't start going through so much oil until recently, like somethings happend. I always thought blow by due to poor compression was more of a gradual thing.

 

quote:Originally posted by spoulson:
Is it reasonable to reloate the PCV hose to a non-pressurized source, such as where the breather hose goes before the turbo? There are some guy's over at DSMTalk that use a catch can for the breather and PCV. Not sure how that works out though.

 

I use a catch can. I have the VC breather and PCV both routed into a brass "T" fitting, which then goes into the catch can. A line from the catch can then goes to my Dejon intake pipe. The charcoal canister just vents to atmosphere. I got my catchcan from RRE, and it came with a filter on the top, but I removed that and closed it off. The VC breather and PCV were both designed by the factory to see vacuum, so they could vent into the intake, so I thought I'd retain this system, and just put the catchcan in there to remove the oily crap.