To pcv or not to pcv...that's the question

[ollykiwi3]

Have a standard pcv valve setup on my 1992 HO motor. New pcv valve and screen and the baffle plate on intake manifold was cleaned before assembling motor.
Last couple of times I removed the upper plenum I found the intake runners quite wet with oil. Sometimes smell oil from exhaust and tail pipes do show signs of oil burn and stain.

Not strictly MS question ,but could the oil affect my AFR readings?

1) could modifying the engine from standard cause the pcv valve to not work as intended or are they pretty fool proof?

2) Would removing the pcv system and replacing with a vent and catch bottle create any other problems?

The valve cover has a breather nipple that goes into the throttle body upstream and is clean, so no oil coming from the valve covers.
AFR jumps a bit at idle. I will post log in another post along with a hunting idle problem so please don't hassle me for a log on this issue..just after a couple of thoughts from people on this pcv thing.
Cheers

[nathanhardy]

so is this a turbo setup? if not id be worried about the blow by causing the oil spray getting into the intake if its turbo it's more normal because of boost.. I run a boosted car and i have a catch can installed in place of the PVC currently i recirculate it back into my intake but i'm going to change that and just vent to atmosphere because i still get some oil into my intake and id like to keep the engine clean .. to answer your question yes oil will throw off the AFR.. the first time i had my engine built the guys that did it screwed up and honed the cylinders out to .015 instead of .005 i could never get the afr's to be stable.. I don't see installing a catch can on a older style engine being an issue... like i said if its more then a oil film i'd be concerned about clearances.

[ollykiwi3]

Hi
No it's not a turbo.
Leak down test all below 10% so blow by is not a major factor. The valve cover breather barely has anything coming out. I can put a piece of tissue paper over it and it barely moves.
Just wondering if the pcv valve is not compatible with the motor now I've modified it.
I can't feel much air coming out the manifold breather where the pcv sits either. Bit strange really.
Anyhow, I might just disconnect it for a bit to see what happens.
Thanks for your thoughts.
That's a bummer about your cylinder machining. Sux when you pay professionals to do a job and they screw it up.

[Peter Florance]

I've had motors make a little more power with PCV connected.
But oil reduces octane, so you will likely need a separator system.

[krisr]

I personally run a sealed catch can on all my cars with a PCV. It just catches the oil mist from the PCV back into the manifold and I simply just empty the can each oil change (~7000mi). The cans I use are made by Elite Engineering, but i'm sure you can get cheaper elsewhere. Elite's can's are made specifically for LSx motors but I managed to find a bolt hole in my Pontiac cylinder head for the can/bracket.

Not using PCV and venting to atmo either leaves oil residue at the can and/or your engine bay stank of oil I found.

[nathanhardy]

That's a bummer about your cylinder machining. Sux when you pay professionals to do a job and they screw it up.

tell my about it they did it twice to me...

I've always understood the pvc to be an emissions controlling device the early v8 just had a tube going to the ground i do not see any issue with you disconnecting it.. a can i'd look in to is the gen 2 misomoto or build your own. i also perfer to have my drain back into the oil pan that way i never have to deal with it... just don't buy into the myth that that'll hurt your motor.

[ollykiwi3]

I personally run a sealed catch can on all my cars with a PCV. It just catches the oil mist from the PCV back into the manifold and I simply just empty the can each oil change (~7000mi). The cans I use are made by Elite Engineering, but i'm sure you can get cheaper elsewhere. Elite's can's are made specifically for LSx motors but I managed to find a bolt hole in my Pontiac cylinder head for the can/bracket.

Not using PCV and venting to atmo either leaves oil residue at the can and/or your engine bay stank of oil I found.

So how does this system work? Pcv valve, hose , can , hose back to manifold?
Does the can have some kind of internal swirl or separator function to remove oil mist?
Any chance you could put up a pic of your one
Cheers

all good, just found them on elite website..

[billr]

First, use a clear hose from the PCV valve to the intake, see if that is really where the oil is coming from. Yeah, a catch-can will do the same, but a lot more trouble to try. I feel it is best to ventilate the crankcase somehow, to flush out some nasty combustion gases that normally blow past the piston rings. Those old "road draft" tubes could do it, as long as the vehicle was moving, not stuck in traffic a lot, but they were also a great way for road dust and grit to get into the oil. The PCV valve is, perhaps, the only emissions device that is a "win" all the way around for anything other than pure race vehicles.

[ollykiwi3]

Hi again. So I've finally got around to doing something about this pcv issue.
Have been using quite a bit of oil, and I'm not 100% it's all going through the he pcv system as some may be oil blow by, but unlikely at this stage.oil was forming in the intake plenum.
Part of my issue with this problem has been a hunting at idle on first start, and I've tried all sorts to stop it.
I've been curious about the possibility of the pcv valve opening and closing at idle creating a fluctuation, so today I disconnected it to see what happened.
I adjusted the idle screw up 1turn to compensate for the lack of air leak through the pcv, and blanked off the suction bleed on the manifold.

It started right up and went to a steady stable idle which it's never done before,if a little high ,but I adjusted back down to normal speed...great news.

1) Now that I have that figured out after a couple of years, how do I decide on the right pcv valve for the system?

Obviously this one isn't quite right. It's the standard one for the original HO motor, but I guess it was designed with more vacuum in mind than what I have right now. I'm idling at950rpm and 50 - 55kpa. Originally idling at 750 at 35kpa on the standard motor.
2) Anyone have a similar idle condition and runs a pcv valve that they could tell me what it is from?
My one is a motorc raft ev140. Although I think the original one was ev98?

I have connected up a vacuum canister now and reconnected pcv valve, and will run it for a while to see how much oil appears, but it's winter here now so not too much driving at the moment.

Any thoughts appreciated.
Cheers

[billr]

There are some GM-style PCV valves that are simple orifices, no springy poppet; I guess just some kind of restricting orifice can work OK.

[ollykiwi3]

Thanks bill
I was reading up on this and one article states that some manufacturers don't use pcv valve as such ,but use a metered orifice with a baffle to seperate oil/mist. This way it's always got a scavenge, but doesn't fluctuate like mine does.
I may just make a fitting to replace the valve and try some different size holes.

[billr]

Me too! I am always fussing with getting a good idle, your thread reminded me to try eliminating the fluctuating-PCV as an issue.

[ollykiwi3]

I made an aluminium fitting last night with a 4mm hole in it and it seems to have made it a lot more stable. I need to play with hole size and throttle blade set screw a bit now to find a good balance.
I think a smaller hole,maybe 3mm and more throttle blade opening might help to stabilise it.
With the old pcv valve having more flow than the hole I just put in the fitting, I had to have the throttle set screw backed right out so it was barely open. Now I can open up about a turn on the set screw and allow more air in the throttle body.
Will see how it goes
Hope it gives you some inspiration to fix yours.

[billr]

Yeah, I have mine made, with a .050" hole. I'll start drilling it larger when I get the engine running. Do you understand that the disadvantage to a fixed orifice like this is that purging flow from the crankcase will be reduced when the engine is pulling hard and MAP is high? The spring-loaded ones compensate for this by going open more at high MAP. I wonder, how do the boosted guys handle this, where MAP will go higher than crankcase pressure, even ignoring blow-by?

[ollykiwi3]

Yeah. Understand The compromise.gues it's trial and error to see how the scavenging goes. We could always spend the extra money on the Werner adjustable one, but where would the fun in that be.
No idea how the boosted guys get on. I'm having enough trouble of my own

[billr]

Maybe they, too, use an orifice and the boost blows back through the crankcase and out the fresh air "inlet"?

[turbo conversion]

On my boosted engine I have 2 catch cans installed with a stock pcv valve.

The reason I use a stock pcv valve is under boost the check valve will seat under boost so almost no boost into the crank case.

One catch can is between the crank case vent and the pcv valve.

The second catch can is between the breather on the valve cover and the air inlet just after the air filter (pre turbo).

Between the baffling in the crank case and the baffling in the valve cover and the catch cans My intake system is dry.

I have also mounted the catch cans lower than where they are attached to the engine so maybe a little more affect separating oil vapor with gravity.

David

[billr]

So, under boost there is no fresh-air purging through the crankcase, only blow-by escaping back out the inlet? I'm not saying that is a real problem, just trying to understand.

[turbo conversion]

So, under boost there is no fresh-air purging through the crankcase, only blow-by escaping back out the inlet? I'm not saying that is a real problem, just trying to understand.

That is not correct, under boost the crank case is not under pressure due to the low pressure created by the intake.

This is why OEM use this same system but without the catch cans,

Unless there is excessive blow by from worn rings this system works very well.

Some do this without a pcv valve but the basic pluming is the same.

David

EDIT: word

[kaeman]

I fixed pcv and all the associated plumbing by installing a dry sump oil system, I have vacuum on the crankcase at low rpm and higher vacuum on the crankcase at higher rpm... it is a little more costly than the pcv valve.... about 3000 dollars, pump, pump drive belt system, reservoir, oil pan, and hoses.....the shoehorn to make all the parts fit in the engine compartment....
I always understood that the pcv valve was one of the smog solutions that was actually a benefit to a good running engine by allowing the pressure in the crankcase to relieve itself into the intake manifold. unless you have bad rings, then the correctly working pcv will actually help with the engine performance.
Just something that was told to me by old school mechanics for many years.....