2007 4.0 v6. Engine was rebuilt after overheating. It has run fine for four months. All of a sudden, lost oil pressure at a traffic light. Checked for oil, it was fine. Mechanic checked and first tested the gauges. Threw a external gauge on it. Engine starts fine , runs fine for five minutes, then loses pressure. We replaced the oil pump, replaced the oil pump drive shaft, new oil filter, thinking it might have collapsed. replaced the oil filter holder bolt to the block because the o ring looked worn. When we dropped the pan to change the oil pump, the sump was clean, no parts or fragments.

Absolutely stumped. Any one ever hear of this or have ideas. The engine sounds great for five minutes then no pressure.

 

How was the external gauge connected? If you used any of the same connections as the dash gauge then I'd try another sampling point. There should be no reason to lose pressure if the pump is good and there are no breaches.