Bypassing PCV

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dlundblad

dlundblad

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This was asked on Jeep Forum and got me to thinking..

Would there be any issues bypassing half of the PCV system. The Jeep 4.0 has 2 elbows attached to the valve cover. The front runs into the air box, but the rear runs into the intake and (I assume?) allows the crankcase fumes/ gases to get burned off with everything else thus allowing cleaner emissions.

Would there be any issues removing the rear line and just installing some sort of crankcase breather filter?

(Those filters remind me too much of K&N and look like a great way to get particles into the engine.
21.gif
)
 
The line from the air box is designed to allow filtered air in, the rear line is the "out" which is vapors/smoke etc.

PCV is almost all benefit with little cost, first question is why? It allows for more power, and decreases oil consumption in properly designed and operating systems.

You could vent the rear tube to the atmosphere, but unless you had some specific problem there would be no benefit...
 
Originally Posted By: SteveSRT8
first question is why?


I think folks think additional power/ fuel efficiency is gained.

I am not looking to do the conversion. My curiosity was only sparked.

My new PCV has less than a year of use on it and operates flawlessly. The grommets are actually rubber that creates a seal and not the hardened leaking plastic stuff.
laugh.gif
 
Originally Posted By: slacktide_bitog
Does your Jeep happen to have a TDI engine swap?


Shhh.

Dont tell Obama.
 
Removing the PCV feed to the intake will dramatically shorten oil life due to a lack of fresh air being drawn through the crankcase. Especially if short trips are involved, as it won't get moisture out of the crankcase as effectively.

It's entirely possible that an engine that sees a lot of short trips but is running a 5k OCI safely might be down to 0 TBN and noticeable moisture in the oil after 2k miles without the PCV.
 
If you are concerned about the liquids making it to your intake, you can put a catcher inline. Its just a tank that you put in between the PCV and the intake that allows any liquids to drop out.
 
I did that as a young (and foolish) man back in '76. Replaced the PCV valve with a road draft tube, thinking it would "run better". Big mistake. After a little while, when I went to add oil, I noticed a build-up of yellowish gel under the oil fill cap. The inside of the engine was becoming a mess. Replaced the PCV valve right away.
 
Originally Posted By: SteveSRT8
The line from the air box is designed to allow filtered air in, the rear line is the "out" which is vapors/smoke etc.

PCV is almost all benefit with little cost, first question is why? It allows for more power, and decreases oil consumption in properly designed and operating systems.

You could vent the rear tube to the atmosphere, but unless you had some specific problem there would be no benefit...


More power?? In 49+ years of working on vehicles that's a new one on me...

As already stated what they do is recycle the blow by back into intake to be burned, vs venting into atmosphere(are first pollution controls to be introduced in late 50s)... I'll agree a properly designed the system doesn't increase or decrease oil consumption...

A plus is the system pulls fresh filtered air into crankcase that will help reduce deposit build up, a properly designed/working PCV system is a win-win...
 
Originally Posted By: dlundblad
This was asked on Jeep Forum and got me to thinking..

Would there be any issues bypassing half of the PCV system. The Jeep 4.0 has 2 elbows attached to the valve cover. The front runs into the air box, but the rear runs into the intake and (I assume?) allows the crankcase fumes/ gases to get burned off with everything else thus allowing cleaner emissions.

Would there be any issues removing the rear line and just installing some sort of crankcase breather filter?

(Those filters remind me too much of K&N and look like a great way to get particles into the engine.
21.gif
)



PCV is a win/win for the engine. It started out as an emission requirement, but it very quickly became obvious that its a GREAT method for keeping the oil cleaner and the engine much freer of sludge. Keeping that line that goes from the crankcase through the PCV valve is ESSENTIAL for sucking the blow-by, moisture, and acid-forming gasses out of the crankcase (its actually a CCV orifice in the case of a Jeep 4.0, there's a subtle difference but it really doesn't matter).

Now the other tube- the one that comes from the airbox, matters a little bit less. Its done the way it is so that in those heavy-load moments with the PCV/CCV system can't keep up, the blow-by that squirts out of the normal PCV inlet will still go into the intake tract and get burned, it just goes in upstream of the throttle instead of into the intake. If you put a GOOD air filter on that inlet line, you can suck the air in from anywhere you want, it doesn't have to come from the intake tract. But there's no real downside to it, and no benefit in re-locating it.
 
Originally Posted By: dlundblad
This was asked on Jeep Forum and got me to thinking..

Would there be any issues bypassing half of the PCV system. The Jeep 4.0 has 2 elbows attached to the valve cover. The front runs into the air box, but the rear runs into the intake and (I assume?) allows the crankcase fumes/ gases to get burned off with everything else thus allowing cleaner emissions.

Would there be any issues removing the rear line and just installing some sort of crankcase breather filter?

(Those filters remind me too much of K&N and look like a great way to get particles into the engine.
21.gif
)


There are several equally valid trains of thought on this... Ultimately, some form of vacuum on the crankcase is a good thing but wether the vacuum comes from the intake or the exhaust is irrelevant re evacuation, although exhaust evac. is better for intake cleanliness...
 
Since we have a PCV teaching seminar going here, let this dummy ask a quesion....
What is the real purpose of the PCV valve itself? What if the PCV system remained exactly the same except that the 'valve' was taken out and the vent side was just 'straight piped' instead?
what is actually opening and closing the valve? Yeah....I know it is pressure differential, but my 3 brain cells are having a hard time grasping exactly what is going on. can someone give me a step by step description?
 
The PCV valve closes in case of backfire, so the pressure pulse is not sent to the crankcase. Also, the vapor is combustible, you do not want to light it and blow off the pan. The orifice used in jeeps is to me a BAD idea.

Rod
 
PCVs cut the flow to a lot less at idle. Otherwise it'd be a huge vacuum leak. If the orifice were idle sized it wouldn't be effective under load. Exceptions abound.

PCVs get blamed for high idles when they stick open. They make sludge when they stick closed. The engine at least can force blowby out the fresh air tube. If you had a breather filter in its place it would ooze oily grime down the valve cover, and, typically, onto the exhaust manifold to stink up the world.
 
But jeeps don't have a pcv system, they have a ccv system.

There is no valve, just a fresh air in and a metered orifice out. Essentially a restricted draft tube. Its almost identical to the older modified cars with the breather filter, except the filtered air comes from the air box and isn't as shiny.
 
I might have to take a couple pics and post a thread. My CTS-V has a aftermarket intake manifold+throttle body which eliminates a valve cover vent tube from connecting to the intake. I installed a mini K&N on the valve cover vent that is left with no where to go. There is still a tube coming from the valley cover to the throttle body.
 
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