hey guys my 91 xj 4.0 has 233000 miles on it, i was driving it around the other day. When its cold it will hold around 50 pounds oil pressure as it warms up it drops some and willstay anywhere from 20-40 pounds. As i rolled up to a stop yesterday after about an hr of driving i looked down and as i stopped the oil pressure bottomed out but as soon as i hit the gas it went back up to about thirty pounds. It runs great no smoking no knocking or anything, my question is do xjs have any certain problems, as far as oil pressure sending unit or oil pump or gauge. Because to me it sounds like oil pump but i just wanted to check first

 

Oil pressure sending unit. I just had a similar problem. But mine was a little worse. I have to insatll a new oil pump and pickup tube as mine is no longer working 100%. Try the Oil pressure sending unit first. If that doesn't fix the problem, you may be looking at an oil pump.