Jeep: no oil pressure, main bearings, jeep cherokee

Question
I have a 93 jeep cherokee with a 2.5 engine. It runs good but as soon as the engine warms up, it goes down to zero oil pressure. this is on a guage that we installed-- the kind where the oil runs up  the tube. we have changed the rod and main bearings and they meet plasitiguage specs. do you have any suggestions?  

Answer
Oil pressure is created by close tolerances between engine components and there are lots more  than rod and mail bearings.  My guess is that your engine needs a rebuild by boring, new pistons, new camshaft and bearings, grind the crankshaft with new bearings, and a new oil pump.