PCV spring tension w/ valve cover breather? (L28ET)

[tyson]

My L28ET gives some smoke out of the valve breather while driving around, not a terrible amount but I can smell it at times.

 

Yesterday I checked & cleaned the PCV valve under the intake and noticed that when blowing compressed air through the valve it takes a moderate amount of pressure to open (I have no idea what PSI).

 

Now, if the valve cover breather is vented to the atmosphere, the lower end shouldn't have much more (if any) pressure than the top end correct? I'm wondering if the PCV valve never opens because of this, and therefore sends all the fumes/vapor out the valve cover breather?

 

Thoughts?

[BluDestiny]

Valve cover breather is under a vacuum, that's why it's supposed to go to the intake. and that's also why the pcv should be easier to open, it has a vacuum acting on it since it's connected to the intake.

 

The crank case can build up pressure, and if you can blow open your pcv valve with your breath, then it's more than likely good. It is possible for gunk to get in the spring area and harden from what I've been told. Never experienced it myself.

[tyson]

Valve cover breather is under a vacuum, that's why it's supposed to go to the intake. and that's also why the pcv should be easier to open, it has a vacuum acting on it since it's connected to the intake.

 

The crank case can build up pressure, and if you can blow open your pcv valve with your breath, then it's more than likely good. It is possible for gunk to get in the spring area and harden from what I've been told. Never experienced it myself.

 

Blu, the valve cover just has a filter breather on it. It's vented to the air.

 

I didn't try blowing the valve open with my breath, and I doubt I'd be able to.

[NewZed]

The PCV valve is more complicated than it looks. From what I can figure out,the spring is actually tuned for the application. In most cases, the valve sits slightly open, and is moved either way by vacuum or backfire (or boost, I assume). You should probably be able to blow through it when it's off the engine. I know that you can blow through the NA valves, I doubt that turbo valves are much different, if at all, at zero intake vacuum (between WOT and boost).

 

Google some images of "PCV valve" and you'll get some ideas.

[Tony D]

First incorrect ass u mption in this thread is that the valve cover is vented to air. It's not. Blu & NewZed got it right each in parts

The PCV SYSTEM keeps the crankcase under VACUUM at ALL TIMES.

Hence POSITIVE Crankcase Ventilation (PCV)...

If you read the FSM they explain the function of the manifold valve is to regulate and control how MUCH vacuum is supplied. Obviously at WOT there is NO vacuum in the manifold to positively evacuate the crankcase, and the valve shuts completely. Likewise due to internal machining on the body and the shuttle inside with combination with the spring, when at idle the valve is close to being fully closed to prevent entrainment of excessive oil into the manifold.

Where it's full open is under moderate throttle and load situations like light cruise, allowing medium vacuum in the manifold to draw from the top, filtered air into the crankcase and evacuating it through the combustion process. This happens because the vacuum present at the manifold is higher than the vacuum present in the intake at the front of the carbs or throttle body.

When you go WOT, or an ET goes on-boost, the PCV Closes and built up blobby crankcase pressure it evacuated by the low pressure present in the intake tract between the Air Filter and the Throttle Body. This is several inches of water vacuum, and effectively siphons out the then sealed crankcase to similar pressure if your rings are in decent shape.

Ideally the crankcase is maintained at marginally negative pressure of 1-4" WaterColumn at all iMessage. Generally without a plugged air liter you won't see that under WOT. You won't see that with a K&N in the stock housing nor with a similar substitute CAI due to the lower filter restriction.

Yes a CAI makes oil leaks...I digress...

[Gollum]

So what you're sayin' tony... is that I should go put a clogged filter on my car to fix my oil leak!!! Man I've been hunting that one down for a long time.

 

Sounds to me like your PCV valve might need replacing, and guess what? They're CHEAP!!! Just for giggles I'd buy a new one, pull the old one, and them compare them side by side with a vacuum gauge and a air compressor to see at what points it seems to be operating. Then you'll know just how bad, if at all, your old PCV is. Also keep in mind that like CHT, or O2 sensors bought from your local autoreillyapa, your mileage may vary. I've known people who've bought sensors in batches of 5 just to find ONE that's "close" to FSM spec. Sometimes NOS nissan parts ARE worth the extra coin, just for less hassle.

[Randall]

So what would be the best way to set up a PCV on an L28et setup without the original stock emissions/throttle body on the intake manifold?

 

Im guessing easiest would be to hook the stock PCV valve up like normal to the side of the block and run the valve cover to a spot between the air filter and the turbo compressor...

 

Or would it be easier to just ditch the PCV valve and run the exit on the side of the block to an exhaust evacuation and again run the valve cover to a spot between the air filter and the turbo compressor...