99 and up 4.0 had issues with the cam bearings wearing prematurely. This will cause low oil pressure but no knock.
I'd wager at that mileage you will have a combination of both oil pump wear and also cam bearing wear.
The oil pump replacement would also allow replacement of the rear main seal (probably leaking) and oil pan gasket. That could address multiple issues at once.
The cam bearings however require complete engine teardown.
Id wager $200 worth of oil pump, RMS and gaskets against putting another $3500 (reman engine + labor) into a 218k mile XJ.
