I have a 98 2d 4cy with 160,000 miles. When I bought it the oil pressure idiot light was on. I started with the oil pressure sending unit then I went on to replace the oil pump, crank and rod bearings, the instrument cluster with non idiot light version, and finally a mechanical gauge. Oil pressure when cold is at about 55 but as it warms it steadily drops to almost zero once at operating temp. Under acceleration it will be about 20 but fall right back down close to zero. Their is no ticking from the valvetrain and I can see oil getting to the vavles. I am pulling my hair out with this problem. When I pulled the bearings the crank bearings were not that bad but got replaced anyways but the rod bearings were worn into the copper. I may have screwed this up when I just installed new but the same size rod bearings that came out instead of measuring the clearance and getting the right ones. Where do I go from here?

 

Check your cam bearings?

And yes, you may have screwed up with the rod bearings.