Thanks to all the help posted here--both in direct answer to my queries and in previous posts, going back several years.
The 1998 4.0 is running, and seems surprisingly gutty.
However, I had no history with the Cherokee, so I don't know if the issues are new or old.
Starts and runs well, but oil pressure drops after it gets fully warmed up. I can maintain the required 10 PSI for 1000 RPM, but at idle it drops below 10 PSI. I also hear what I think is the infamous lifter tap- although it could be a con rod.

My plan-- I plan to drop the pan and replace the oil pump. Since I am already in that far, I will also do the main and con rod bearings as well as the rear main seal.

My questions--
1) I read that the cam bearings at high mileages allow oil to escape and that lowers oil pressure. Should I use a hi volume oil pump?
2) Does a hi volume oil pump put excess load on whatever drives the oil pump? Is this a concern?
3) Is there any downside to installing a hi volume oil pump?

Your comments are encouraged.

Thanks,
Michael

 

Have you tried a new oil pressure sensor? might be worth the $20-30.

Low oil pressure is going to be caused by either a bad pump or bad cam bearings. I'd start with a new standard volume pump and see what happens.

if the cam bearings are worn to the point that your pressure is that low, a high volume pump ain't gonna fix it. Save your money.

 

Thanks. I generally shy away from Hi Volums oil pumps---
I respect the OEM engineers, and I question the extra HP to drive the Hi Volume pump--was the drive system designed to handle that extra load.( Early small block Fords drove the oil pump off a too small hex in the bottom of the distributor, and the extra torque req'd to drive a hi volume pump could round off the corners of the hex drive--Ford later corrected this with a larger hex--but it illustrates the problem s associated with swapping out oem parts for "better" ones.

My only question was whether the cam bearing would now make the hi volume pump a better choice.

You answered that, Thanks.