PCV valve in a 4.0?

[JeepNoob]

Yeah, I know they don't have one. Some people don't though. Case in point, was looking at another Jeep that came by the school shop (a YJ with a 4.0 to be exact) and this thing was a mess, especially under the hood. One thing I noticed was the rear fresh air hose that runs from the valve cover to the intake manifold was missing. One of my instructors made the comment that the PCV valve/system needed to be re-installed. I pointed out that they never came with a PCV valve. The response I got back (after a bit of arguing and explaining in regards to the fresh air system) was "Why the Hell not?! If there's one engine that needs a PCV valve, it's these things!"

That got me thinking, why don't the 4.0's have a PCV valve and has anybody ever tried installing one? Seems to me like it would be easy enough to splice one into that rear-most hose/line on the back of the valve cover... If anybody has, what sort of PCV valve did you use and how did you install it? What were the positives and negatives of installing a PCV valve?

 

[ehall]

A PCV valve is literally just a weight that sits on an orifice in the valve cover. When you rev the engine, intake vacuum builds up and sucks the weight off the orifice, thereby allowing outside air to draw the combustion gasses into the intake manifold. It also works if combustion gasses build up their own pressure, they will push the weight off the orifice and make their own release. Its basically a regulator.

Jeep motors use a system called CCV that is always open, fresh air can always come in one and get pulled into the intake as pressure in the system changes. There is no valve, its just open. However it does have a small hole so that it is restricted, so it only works when pressure is there.

You can put a valve in the rear if you want, some people have done it when they couldn't find an elbow. No reason to do it except as a patch job.

Ask your teacher, what is the benefit of having the valve closed

 

[JeepNoob]

My understanding was a PCV valve allowed some vacuum to remain in the crankcase/oil pan/wherever when the engine was shut off, thereby helping alleviate oil leaks. But I guess it is a silly idea since 4.0's never leak oil. Like, never ever. *roll eyes*

 

[ehall]

PCV and CCV both go to neutral atmosphere through the valve cover inlet if nothing else (undesirable)