stop oil pressure build up & blowby

I believe I have found the answer to the never ending battle of oil in the air box and excessive leaking from the rear main seal. do not be confused most jeep with over 100k will leak some from the rear seal, but i have been able to stop oil from entering the air box, and stop the rear seal from leaking. look on the top side of the intake manifold you will see two small vacuum lines on the outer edge of your intake, they are very similar in size. take both lines of your intake making sure you know where they go back. replace these, you can buy replacement lines at napa cheap. while you have the lines off remove the two couplers from the intake where the lines were connected. spray them with intake cleaner, and blow them out with an air gun. most times the one on the left will be completely clogged, causing you build in pressure. once they are clean put them back and connect your new lines. hope this helps, it has worked on mine no problems for over a month.

I would add to this that the early 4.0 had sharp 90 degree elbows in the vacuum line. There was an upgrade replacement with gentler curves in the elbows and it seemed to help. The vacuum lines themselves build up a sort of arterial plaque inside and replacement or a thorough cleaning can help a lot.