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PCV System and Maintenance

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There are lots of bits and pieces in threads here and there about the Subaru PCV valve. Mmaybe my search game isn't up to snuff but I had a hard time finding what I needed. So after trawling through various forums, I wanted to consolidated the information that I’ve gathered regarding the Subaru EJ255/7 PCV (Positive Crankcase Ventilation) system. I will add additional posts to this thread with more information, and some pics as well.



Bottom-line up front:


AFAIK there are no specific maintenance intervals for the PCV valve. Some places say check/replace every 30K miles. The biggest thing that made me look into the PCV system was finding oil in my intercooler piping, as it’s one way for oil to wind up in that tract.


If you run an FMIC the PCV Valve/system is actually really easy to get to, while a TMIC will require removal. Look behind the intake manifold, under the main engine harness bracket, and between the throttle body and the turbo inlet. Voila, you should see a 3-way black plastic assembly with a silver nipple pointing towards the throttle-body, an end terminating into a white plastic piece connected to a sensor, and the final end pointing down towards the crankcase. Once you get to you have to deal with the “click-r” clamps to separate it from the bottom hose. There are special tools that can open this, but it’s easy enough to shimmy it open with a small, correctly-placed flathead, and somewhat difficultly closed with a small channel-lock (at least that’s what I used). The white plastic piece can be disconnected from the hose that runs under the intake manifold, then can be unclipped from the 3-way plastic piece.


The actual PCV valve is stuck in the plastic housing (I’ve read that people are able to remove it, I wasn’t so fortunate). Some OE manufacturers sell the whole assembly as one (Standard Intermotor part V576 for the 2007 LGT), otherwise Subaru sells the plastic assembly and valve separately.


How do you know if your PCV valve is bad? Give it a shake. If it rattles you are good to go. If not, either replace it, or give it a shot of brakleen to open it up. It’s a one-way valve, so you should be able to blow through the threaded end without issue, and should be unable to pass air through the nipple.


Something that not many people have noted was the secondary PCV system that connects breathes/vents from the valve covers to the turbo inlet pipe. The plastic pipe that runs between the valve covers and connects to the turbo inlet can get really gunked up with love-juice. I don’t know how important it is to repair/replace, but it looks like an overlooked area that could cause some bad juju if clogged or cracked.

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General Information


- What is the PCV System? In short, it’s an engine-protection, emissions-related system that vents blow-by gasses (gasses that pass from the cylinder combustion chamber, through the ringlands, and down into the crankcase) back into the intake system (as opposed to venting to air).


- At the very basic level, a PCV system is a one-way valve out of the crankcase that allows the excessive pressure from blow-by to normalize.

- The EJ255/7 PCV system is a little more complicated than a single one-way valve due in part to turbocharging. There are actually 2 components of the PCV system, and both systems behave differently depending on intake manifold pressure.

- That being said, a faulty PCV valve that fails to open would result in decreased volumetric efficiency, and makes it into the FSM as a “sometimes” cause for: low output, hesitation and poor acceleration; surging; after-burning in the exhaust system; and excessive oil-consumption. The FSM also includes the PCV valve as a “rare” cause for: stalling after combustion, as well as a rough idle and engine stall.

- Despite being a part of several issues outlined by the FSM, neither the 2007 LGT Manual nor FSM dictate a PCV inspection/valve replacement maintenance interval.


So let’s take a look at the 2007 Legacy GT EJ255 PCV system. The specific parts can vary both per model year, as well as per EJ255/7 vehicle utilization, but will basically follow the same pattern. I’ve marked off the 2 systems in different colors. The system is located underneath the TMIC, behind the intake manifold, and under the main engine wiring bracket.



System Orange:

- Here gasses travel from the crankcase into a PCV Assembly (3-way plastic housing with the metal PCV valve branching out into the intake manifold. Blow-by gasses can travel freely to the turbo inlet no matter the condition, and can enter the intake manifold only under vacuum/no boost. Once the intake manifold starts making boost, the one-way valve shuts down.


- The remaining branch connects to a white plastic “PCV Diagnostic Sensor,” which acts as a pass-through that connects to another hose that leads to the turbo inlet. This white piece clips onto the PCV Assembly, and has a socket that literally just grounds the connecting pigtail.


System Yellow:

- While this is part of the PCV system, this actually involves the valve cover gasket. I still don’t know exactly how or why, but according to what I read under vacuum/no boost air will travel from the inlet and into the valve covers and prevent the crankcase from having negative pressure (again, I’m not 100% on this, but people more attuned to the ways of Subaru have spoken)

- Under boost and higher blow-by pressures, this system will act as a secondary path for gasses to escape.


Edited by Subsandwich
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PCV Inspection/Maintenance


System Orange:

- Required Parts: PCV Valve (Subaru Part 11810AA040), PCV Connector (Subaru Part 11821AA580). If you are able to remove the valve from the connector, lucky you, otherwise you’ll need both. Standard Intermotor makes a replacement part that has both pieces, V576, for cheaper than the official Subaru valve alone.


- Other Subaru pieces may work with some finangling, but will likely not connect directly to the “PCV sensor” pieces. Again, this just grounds the connected pigtail, so you don’t technically “need” this part for a functioning system, as long as you ground the pigtail with something else.



- To inspect, give it a shake. If it makes a noise, your valve is just fine. But hey! Might as well replace it while you’re here right? Or at least clean it. I didn’t have the complete assembly when I did mine, so I ended up just cleaning it out with some brakleen until it rattled again. Luckily I have an FMIC so it’s not too much of a pain to get to.



System Yellow:

- I haven't seen anyone really discuss this, but it may be worthwhile to inspect the PCV Pipe that connects the 2 valve cover vents to the Turbo inlet. Mine had weird orange gunk caked to the walls of the pipe, but it wasn't even 20% occluded so I think it's fine.

- Be wary of messing with the pipe too much though! I tried removing mine (AFAIK it's held on by bolts that go to the Intake Manifold) but one of the bolts wouldn't unscrew (I think the metal threaded fitting in the intake manifold may have separated from the actual manifold, and now I can't actually take the screw out despite using extractors and prying and stuff).





Edited by Subsandwich
adding info of PCV Pipe
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