Hi I just bought my second WJ with a 4.0 I6 and it's got oil pressure problems.
when i bought it it had too much oil in it and ticked like crazy so i changed the oil and filter to 10w 30 mineral oil.
The ticking disappeared and it ran fine but when it's reached operating temp the oil pressure goes down slowly and finally to 0 and the check gauges light turns on.
It started knocking quite badly and i have to rev it to about 2.3k rpm for the oil pressure to raise. I then bought engine flush that i ran for 30 min when driving then changed oil and filter again.
I cold started it 6 hours later and it was quiet no knock that o heard and ran good with the oil pressure in the middle on the gauge so i took it for a drive and when it reached operating temp the oil pressure went down to the last mark on the gauge and the engine was knocking a little.
I am thinking of just replacing rod bearings and oil pump but im afraid more damage has been done with driving it like this.

 

You will know for sure when you get in there. I'd replace main bearings too. If there is metal in the pan, I'd tear down and clean completely. Cut open the oil filter and see what is in the element pleats. They will tell a story too..................