Why does my 91 cherokee 4.0 have alot of pressure in my crank case causing jeep to leak oil... What could be the cause and how can it be fixed

 

Make sure the tubes coming out of the valve cover are free of obstructions.

Otherwise, you just may have an aging engine with leaky gaskets.

Or you could have worn rings, scored cylinder walls, or a broken/cracked piston(s).

 

A stuck/bad PCV valve can cause pressure to build up. Does it run rough at all? Is there enough pressure to push the dipstick out?

 

These don't have PCV valves.

 

Yep, should have read the year of his Jeep first. The early 4.0's just had vents right? CCV?