Blocking Rb25Det Pcv

[Trozzle]

Did a search, most results were for RB26 and none seemed really relevant enough to bump with my question.

Recently I began to hear a hissing type of sound from my engine bay, and upon inspection of the PCV hose I've noticed there was a small split where it went onto the rocker cover. At the time I just too it off, cleaned the end of the hose, and stuck it back on - hissing sound appeared to vanish even though I didn't fix anything (just didn't have time then). However recently my car has begun idling at around 1200rpm even when warm, it's starting to drive me insane. I'm guessing that it's likely an air leak post-throttle body and I'm gonna point my finger at the PCV first anyway. Worst case is it's something else.

I'm currently running a catch can setup where hose connects the two rocker cover outlets, and then the catch can is plumed into the exhaust side. Catch can is also plumbed into intake piping before the turbo. If I'm correct, I should be able to block the PCV and not worry at all about pressure buildup since the catch can will take care of that, yes?

If so, what do I need to get to block it off??

[Room42]

Sounds like your iac valve. (Idle air control) Mine does the same thing but I have been too lazy to fix it as it isn't as bad as yours yet. Lazy I know and I'm going to do it now. If you know nothing about it then here is a link to help you. http://www.skylinesaustralia.com/forums/topic/110431-diy-aac-valve-cleaning-idle-reset/page__hl__iac+clean

If you are going to block the pcv valve (positive crankcase ventilation valve) then you gotta block of the bit on the intake manifold so it doesn't suck in air. It might throw your tune off, I don't know.

[bubba]

You can't block the PCV valve and run a closed loop breather system.

[Trozzle]

Sounds like your iac valve. (Idle air control) Mine does the same thing but I have been too lazy to fix it as it isn't as bad as yours yet. Lazy I know and I'm going to do it now. If you know nothing about it then here is a link to help you. http://www.skylinesa...__hl__iac+clean

If you are going to block the pcv valve (positive crankcase ventilation valve) then you gotta block of the bit on the intake manifold so it doesn't suck in air. It might throw your tune off, I don't know.

Yeah I figure it's likely to do with that anyway, just thought I'd consider the PCV first up since I need to replace the hose anyway. IAC can suck my balls, I'll look at it....some other time cheers for the link though bud

You can't block the PCV valve and run a closed loop breather system.

I don't entirely understand how the PCV works, but I can't see why what I suggested wouldn't act the same way. Unless of course the idea of the PCV going to the manifold is to create vacuum in the crank case? Otherwise my idea will simply see it at a neutral pressure since anything positive will simply vent through my catch can setup and back into the intake.

[Room42]

You can't block the PCV valve and run a closed loop breather system.

Would you just run the rocker covers to the can and then back to the manifold?

Anyway I just went outside and took the iac valve off, pulled it to bits, noted how many turns the screw was in, cleaned it out with clr clear, dried it with the compressor and put it back in. I put the screw back in a couple of extra turns. The car started with less of a rev and is idling nicely at just under 800 rpm. Easy as

[bubba]

No, you can't do that.

If you want to run a closed loop system (plumback, recirculating, whatever you want to call it) then you use an oil/air separator (baffled catch can) and plumb it inline between the cam breathers and the intake pipe.

If you want to block the PCV you HAVE to run an atmo system or you will pressurise the hell out of your crankcase and start spewing oil out places.

When I bought my car the guy thought the turbo was fkd, it would blow HUGE clouds of oil smoke when it hit boost.. he had the breathers set up incorrectly. I fixed the breathers and the turbo was still going strong when I upgraded it.

My current setup is atmo: PCV valve blocked, cam covers vented to an atmo breathing catch can and a vent from the dipstick to the catch (NOT a drain).

[Room42]

On the iac subject, I went for a quick drive to get it to operating temp. It was a lot nicer to drive and shift gears just cruising. When I got back it was idling at 550 rpm. I fixed it with the hand controller and its now at 700 rpm. I cant believe I was too slack to fix it when it was that easy. Haha I earned myself a beer

[DaveO74]

Why can't you just put a new hose on the pcv? Would cost you what, max 10bux from supercrap or whoever.

[Crans]

Where do you buy a new hose and valve?

[gotRICE?]

The valve new from Nissan, and the hose, get one from a wrecker.

[jjman]

nissan genuine- any dealer can get it for you (rip off).

Or just set the venting up right n block off the PCV n stop bad oily vapours going into your inlet manifold n doing things it shouldnt.

Especially an issue now when cars are getting higher in the k's n more blowby n vapours in the rocker covers to then end up in the intake plenum.

-oil vapour in the intake charge is a terrible creator of detonation... N whats one thing that RB's hate?....

[Trozzle]

No, you can't do that.

If you want to run a closed loop system (plumback, recirculating, whatever you want to call it) then you use an oil/air separator (baffled catch can) and plumb it inline between the cam breathers and the intake pipe.

If you want to block the PCV you HAVE to run an atmo system or you will pressurise the hell out of your crankcase and start spewing oil out places.

When I bought my car the guy thought the turbo was fkd, it would blow HUGE clouds of oil smoke when it hit boost.. he had the breathers set up incorrectly. I fixed the breathers and the turbo was still going strong when I upgraded it.

My current setup is atmo: PCV valve blocked, cam covers vented to an atmo breathing catch can and a vent from the dipstick to the catch (NOT a drain).

EDIT: reading what you've said for the third or fourth time, I'm starting to think that's exactly what I'm describing (though I'm unsure if my can is baffled - don't know what was put inside it when it was made by fabricator). In any case, my can is in-line with the breathers and intake piping, and has never collected a drop of oil anyway.

I still can't fathom how my setup won't work. the hose from my exhaust rocker goes to the bottom of my catch can. Then from the top of my catch can is another hose that leads to the intake pipe BEFORE the turbo. There are no 1-way valves between my exhaust rocker outlet and the intake hose. Nothing to stop any pressure from the rocker cover from escaping all the way through to the intake (and ultimately running back through the engine and out the exhaust).

To further confirm this, when I had my turbo off last I blew into the intake hose of the system with my mouth, and in turn received a splatter of oil in my face from the turbo oil drain.

To me, this says that any pressure inside my rocker covers will be able to equalise via my catch can intake return hose.

[jjman]

that system still works because the gases/oil from the rocker cover still needs to go through the catch can meaning the oil is separated or at least mostly separated from the air before it ends up in the intake pipe.

if in doubt pull the hose off where it attaches to the intake pipe n see if there is any oily residue making it to there. If not, it is doing its job. If there is, more baffling needed (or it is residue from before the catchcan was plumbed in- so wipe of the residue, n check for residue in another 1000-2000km time)

make sense?

[Trozzle]

that system still works because the gases/oil from the rocker cover still needs to go through the catch can meaning the oil is separated or at least mostly separated from the air before it ends up in the intake pipe.

if in doubt pull the hose off where it attaches to the intake pipe n see if there is any oily residue making it to there. If not, it is doing its job. If there is, more baffling needed (or it is residue from before the catchcan was plumbed in- so wipe of the residue, n check for residue in another 1000-2000km time)

make sense?

Yeah, that's my thoughts exactly. Currently there's only a small amount of residue in the first 15cm of hose after the rocker cover, and absolutely nothing drains from the can. I don't believe the can can be opened, so hopefully it doesn't require any baffling. I don't anticipate it actually getting anything in it, though after a short trial we'll see what happens and if needed cut it open to put baffling of some kind in.

I was just trying to work out how the system could possible pressurise itself if my setup has no restrictions between the rocker and the intake pipe, allowing free-flowing of gasses. Perhaps Bubba was just misinterpreting what I was saying, or the other way around

[bubba]

You were talking about removing the PCV valve.. you CAN'T do that if you have a plumbed back breather system.

If you look in one of the engine manuals, you will find a schematic of how the breather system is supposed to work.

[Trozzle]

You were talking about removing the PCV valve.. you CAN'T do that if you have a plumbed back breather system.

If you look in one of the engine manuals, you will find a schematic of how the breather system is supposed to work.

Now I'm confused....I think I've either used the wrong name for something, or misunderstand something.

From what I understand, there's a hose going from the inlet rocker cover to the front of the plenum, with a one-way valve in it that allows flow from the rocker cover side through to the plenum side but not the other way. Blocking/removing this valve and hose will cause pressure to build up inside the oil system, correct? I mean completely doing away with it. Not just removing the valve but leaving the hose. Blocking off flow in EITHER direction.

Here is a picture of my engine bay (please ignore the black squares, just hiding previous edits as they're irrelevant)

In RED is what I'm talking about. I am suggesting that the flow in either direction of that hose be cut off.

In GREEN is the hose going from my exhaust rocker cover through to the bottom of my catch can

In BLUE is the hose going from the top of my catch can back to my intake piping, BEFORE the inlet of the turbo

As you can see, my inlet and exhaust rocker covers are connected by hose as well, allowing gas to equalise between them both. I know this may not be a PROPER catch can setup, but I didn't set it up and it works.

How will I be pressurising the crank case if I remove the ability for gasses to flow between the two points on the red line??

[bubba]

You will be forcing the blowby gasses to find alternate paths instead of being drawn straight up the intake side of the block and into the intake manifold.

What you are doing, while not technically correct, isn't BAD. It's when people run atmo systems and DON'T block the PCV valve that you get really bad issues.

[gotRICE?]

You will be forcing the blowby gasses to find alternate paths instead of being drawn straight up the intake side of the block and into the intake manifold.

What you are doing, while not technically correct, isn't BAD. It's when people run atmo systems and DON'T block the PCV valve that you get really bad issues.

This is assuming your running an AFM..

Mine is Vented atmo, each breather running into a large can with a filter thingy on it.

I still run the PCV, as when i had it blocked, i was getting blowby at high vaccum, and taking off from lights.

Unsure why, im guessing at idle it wont push it out the breathers?

[bubba]

This is assuming your running an AFM..

Mine is Vented atmo, each breather running into a large can with a filter thingy on it.

I still run the PCV, as when i had it blocked, i was getting blowby at high vaccum, and taking off from lights.

Unsure why, im guessing at idle it wont push it out the breathers?

Yes, only an issue when there is a device metering the incoming air.

Do you have a breather from your crank case to the catch can? IMO this one is pretty critical if blocking the PCV valve and running at atmo system.

The approach I take is to equalise the pressure between the crankcase and the cam covers to prevent any build up of pressure and to ensure the returning oil has a clear path (not fighting gasses moving back up the drains). So I run each cam cover to the catch can and the dipstick to the catch can so that the blowby gasses have a nice easy path.

[gotRICE?]

Yes, only an issue when there is a device metering the incoming air.

Do you have a breather from your crank case to the catch can? IMO this one is pretty critical if blocking the PCV valve and running at atmo system.

No i didnt.

It was a catchcan bought from RIPS. And i was under the impression that they knew how it worked

After researching on here, a member asked to take a look at it and suggested re-instating the pcv. And it solved it.

Works great now. And have since had the plenum apart and its dry as a bone, and silver. So in my case, theres bugger all vapor at idle. So not concerned.

But, just a question. The PCV valve isnt magically connected to the block. its Just a hole in the cam cover. So whats would cause it? Is it just because there is no vaccum to pull the pressure out at idle?

And as i thought,m pressure equalization takes the easiest path. And im f**ked if that would be past the rings as apposed to down a smooth pipe to atmosphere?

Edited August 25, 2011 by gotRICE?