2000 xj with 127K, drops to 0 at hot idle,50 at cold startup,verified with mechanical gage, main and rod bearings are good, plasti-gage showed "desired" clearances according to haynes manual, head was cracked so I replaced it along with the oil pump because the screen was gunked up with sludge. The only thing I can think of is someone already changed out the bearings, but the oil pan didnt appear to have ever been off. Ive run it about 400 miles with 3 oil changes to get the gunk out but still hasnt improved oil pressure. Im at a loss,anyone know of anything else.

Ive inquired about a rebuild locally but the only guy that can do it wont touch a shortblock rebuild, he'll only do long blocks, anyone know of a reputable place to get a reman shortblock?

 

Bearings still the primary suspect here...............

 

Bad cam bearings.

 

I thought cam bearings as well, but it just doesnt make sense when the rod and main bearings look and measure as good as they do, Ive heard all my life it takes a lot to wear out the cam bearings. Im not saying theyre not bad, its just hard to believe they could be with what the others are showing me.

 

As you stated, the rod and main bearings may have been replaced, perhaps the cam bearings were not. Rod and Main bearings are easy enough to replace by just dropping the pan. The cam bearings are different can of worms.

 

it is true that cam bearings do not go bad very often, but if you have low oil, or run to thick of oil in cold weather, this can lead to premature failure. also running at high RPM's for a long period of time in high temp could cause this.

 

Can of worms, you got that right. Im looking for a reman shortblock but with all the junk coming out of china, I dont know who to trust buying one from. 4.0s are really scarce around these parts too,Ill just have to sit back and see what comes along.

 

call these guys http://www.atkvege.com/content/

 

I had the same symptoms with my 96 Grand Cherokee 4.0. Changed the oil to 20/50 and installed a NAPA Gold oil filter. Also put in a pint of Motor Honey additive. Hot idle pressure went from zero to 20 lbs. This is a 205K mile motor and I'm just trying to get a little more life out of her.
Good Luck!