PCV Question(s)

[Grim0013]

I am in the process of getting my '87 GN legal for Northern Virginia emissions, and need to get a PCV setup on the car. I don't know a whole lot about what I need to do to get it legal, not to mention the way things are right now seem a little odd to me.

First, there are currently breathers on the valve covers. From what I have been able to gather, it sounds like I need to get a hold of some stock breathers or the equivalent in order to plumb into the passenger valve cover.

Something I noticed when checking out the vacuum lines; On the rear, passenger side of the vacuum block, there is a line a little larger than the others which goes straight down. It looks like it is connecting to a tube coming up from the block. Is this going to the crank case? Also, if it is, I'm not sure if there was a check valve on there. If there isn't, wouldn't that be pushing boost into the crank case? aka, a bad thing? I blew out the rear main seal not long ago....makes me wonder. Also, if this is plumbing the vacuum block straight to the crank case, wouldn't I then only need to plumb from say, the valve cover to the pre-turbo intake to complete a closed system?


Ultimately, I was thinking it should be set up as such:
(Valve cover) --> (Catch can) --> (Pre-turbo intake)
(Crank case or valve cover) --> (Check valve) --> (Intake manifold) before or after the MAF?

I'm really just basing this on a little internet reading about the purpose of the PCV system and how it is supposed to work. In practice, I have little idea what I should be doing to get this handled. Any help is certainly appreciated.

 

[TR Custom Parts]

Sounds to me like you already have the PCV. It is located on the passenger side of the intake manifold.

 

[Grim0013]

Yeah, I dug out my shop manual CD-ROM, and after looking at that and a few vacuum routing diagrams on gnttype.org, it does look like the PCV is there. What I think they are flagging me on is the valve cover breathers. I think that instead of breathers, they want it plumbed to the PCV or intake, as I assume it is in stock configuration.

So, given that, it looks like I need to figure out what I need in order to get from the valve cover(s) to the pre-turbo intake.

 

[Grim0013]

Another quick question about this: Once I get the parts to go from the valve covers to the intake, should I plumb it in before or after the MAF? The obvious first thought is to put it before the MAF, for more accurate measurements, but I'm not really sure it's the best idea.

If I understand things correctly, when the manifold is in a vacuum state, the PCV will open and draw air from the crankcase into the intake manifold. When the manifold is under boost, the PCV valve will close, preventing boost from reaching the crankcase. It is as this point that the valve cover portion of the system comes into play. In the case of breathers, it allows blow-by gasses to vent to atmosphere. In the case of a system plumbed to the pre-turbo intake, the slight vacuum before the compressor draws the blow-by gasses out through the valve covers and into the intake.

So, my reason for wondering if I should plumb the valve covers before or after the MAF is that the PCV portion of the system goes from the crankcase to the intake manifold, bypassing the MAF. So, since that part of the system bypasses the MAF, should the rest of it? (post-MAF) or should it be measured? (pre-MAF) Does it even matter?

Another consideration I guess is the concern over oil mist. I'll be inserting a catch-can to minimize it, but I'm sure some tiny amount will still get through. While it wouldn't be enough to really bother the compressor and intercooler, could it potentially bother the MAF?


Thanks again for the info.

 

[turbojd]

I have open breathers on my car, and oil misting is not a problem, but if oil misting is a problem you could always use valve cover extensions to raise the breathers some.

 

[Grim0013]

I have open breathers on my car, and oil misting is not a problem, but if oil misting is a problem you could always use valve cover extensions to raise the breathers some.

I was referring to oil mist after I change to a closed system, routing that air back into the intake. An open system, aka breathers, it turns out, will not pass Northern Virginia emissions requirements, PCV or no PCV.