[Biturbos4] Unholy smoke
keman at interwolf.net
Sun Jul 31 23:36:10 EDT 2005
Well, a PCV system for a turbocharged engine is an interesting thing. PCV
stands for Positive Crankcase Ventilation. The sole purpose for a PCV valve
in the past was to allow the vacuum from the intake manifold to draw in
vapors from the crankcase, but prevent things like a backfire (pressurized
intake manifold) from blowing into the crankcase and pushing the front and
rear main seals right out of the engine.
The multiple tubes are for drawing the vapors away from multiple sources--
both valve covers, for instance.
Now, here's the interesting part, and where it gets tricky.
The intake has vacuum on biturbo engines. Sometimes. When it does, air is
drawn from the valve covers and the crankcase. Air out must equal air in
though. So if air is drawn out and there isn't enough cylinder 'blow by'
(air that sneaks past the pistons) to account for what the intake manifold
is drawing in, air is let in. Air being let in must be metered, so the upper
Y pipe is the source for air to enter the engine.
Well, that's fine and all, but what about when there is boost? The intake
manifold is no longer sucking. It's trying to push. So there is a valve
there. No problem! Well. Actually. Wait. There is a problem! Where is that
cylinder blowby going to go? It can't enter the intake manifold- there's
boost there. It can't be trapped. It can't be vented to the atmosphere,
nope.. EPA won't allow that. So it's gotta be burned. Only source in that's
still at remotely atmospheric pressure is the Y pipe. So... in it all goes,
all the cylinder blowby. And along with it, a little bit of oil. The oil
travels along the drivers side of the y pipe, where it gets sucked in by the
drivers side turbo and this is one of the reasons why you see a wet drivers
side bypass valve, typically.
There is a seperator for the crankcase, designed to baffle the blowby and
prevent excess oil from being consumed. That seperator may be messed up on
In addition, there are other potential sources of failure in your PCV
system. The valve itself is supposed to prevent boost from getting into the
cylinders. If it doesn't, it'll push lots of air in and where must that air
go? Into the Y pipe, along with lots of oil. Just like what you're seeing.
So... you have this.. giant.. octipus looking thing. You might wanna try
replacing it. All of it. It's available as one giant assembly. You'll need
some new pinch clamps. You want to replace it all, because it tends to get
brittle and when you start trying to pull it apart, it'll shatter and break
in various areas that you didn't want to replace. :P
Good luck .. there are other things that could cause this, like REAL blowby.
But you shouldn't be seeing that, not without burning a ton of oil and
having an engine with a million miles on it.
----- Original Message -----
From: "Chris Newbold" <chris at newbold.org>
To: "Keman" <keman at interwolf.net>
Cc: <biturbos4 at audifans.com>
Sent: Saturday, July 30, 2005 6:57 PM
Subject: Re: [Biturbos4] Unholy smoke
: Keman <keman at interwolf.net> writes:
: > Any misfire codes? How do the plugs look? PCV system?
: So I tore into the upper part of the induction system this afternoon
: to see if I could find a likely source of oil. The inlet and outlet
: hoses on the driver's side bypass valve were all "fuzzy" with oil, so
: I pulled it: there was enough oil to start a small drip. Little sigh
: of relief here, since it's clearly coming in through the induction and
: not internally.
: So with a sizable quantity of oil making it's way through the driver's
: side of the induction system, I started dismantling bits of the PCV
: system which appear to be plumbed to the driver's side of the Y-pipe.
: Bingo. Pulling that connection at the Y-pipe resulted in another
: drip-drip of oil. Again, not a flood but what seemed to me like a
: significant amount.
: I don't really know what these bits are, but I took pictures so
: hopefully someone can comment and have some ideas about why oil would
: suddenly start getting sucked in this way.
: This one here http://www.newbold.org/~chris/pcv-1.jpg shows the
: doohicky I disconnected from the Y-pipe (red arrow).
: The doohicky above is connected to the thingamibob in this picture
: http://www.newbold.org/~chris/pcv-2.jpg, highlighted by the red arrow
: on the right. This is down near the firewall, in line with the center
: of the V in the block. (The red arrow on the left shows the
: [out-of-focus] point where I disconnected the doohicky from the first
: This thinamibob has five connections: one to each valve cover; one to
: the Y-pipe via the doohicky; one to the underside of the intake
: manifold; and one to the block itself.
: The thinamibob is also all "fuzzy" with oil residue, so it seems
: likely that oil is going in this way...
More information about the Biturbos4