1999 Jeep Cherokee, mileage: 123,000. All six connecting rod bearings failed but the main bearings look like new. All crankshaft bearings are original. Oil pump looks like new. No sludge in engine. I was using 10W-40 oil when oil pressure started to drop to 19 psi at 2000 rpm and then dropped to 11 at idle. I also had added PTF to the oil. I switched to 15W-40 then to another grade of oil but no change in oil pressure. Then I opened the engine and found totally failed connecting rod bearings. Can you suggest why connecting rod bearings failed and everything else seems to be in great shape?
It is not unusual to find connecting rod bearings with more wear than main bearings. The reason is that the rod bearings are much smaller than the main bearings and they take the load from the pistons going up and down. As for your oil pressure, check the oil pressure release spring and valve for proper operation.