I just bought a 93'Bronco XLT w/172K miles in fair conditions. The oil pressure works fine (60 psi cold, 20 warm) and stays this way for long time (2h) IF the truck is sitting in my driveway. As soon I start driving it, the pressure (orig. electric gauge) drops to zero with some intemitent recoveries but finally stays in zero. So far I can't relate it to bumps or sharp turns. After 1-3 mins w/o pressure the hidraulic valve lifters start to clacking with increasing noise. I drive back ASAP. Oil level checked OK before, during and after this episodes. Oil sender replaced. pressure confirmed with mechanical bourdon manometer when normal. Oil & filter changed and filled w/6Qts Quaker State 20-50W. Accuracy of oil dipstick confirmed. After 1 or 2 days, I start the engine and may or may not get pressure the 1st time, but after few tries, the presure shows up again like nothing has happened the engine runs smothly and no noise at all, until you drive it again. No smoke, no overheating, nothing else. I repeated this experiment about 3 times with the same result. I'm convinced the pressure drop is real. Also I thing the engine is not damaged yet. Any simmilar experience? Something loose at the pump? or sucking air?. What about the Hidraulic lifters? I am sure the lifter noise appear about 1 min AFTER the pressure drops, I think it is a consequence and not a cause. Sorry for such long message, any help will be highly appreciated. Frank

It sounds like you may have a sticking bypass valve in your oil pump. This is a fairly common condition, esp if the oil was not changed as often as it should have been. The only way to correct this is to replace the pump. Also, check the condition of the pump drive rod, they can and do fail. If the pump and/or drive rod are not the cause of your problem, then it gets tougher, as you will have to disassemble the engine and check all bearings, including the cam bearings. If you do decide to tear down the engine at some point, pay special attention to the thrust plate at the front of the cam, the oil galley plugs, and the plug at the back of the cam bore. These are known trouble spots. Mike

It sounds like you may have a sticking bypass valve in your oil pump. This is a fairly common condition, esp if the oil was not changed as often as it should have been. The only way to correct this is to replace the pump. Also, check the condition of the pump drive rod, they can and do fail. If the pump and/or drive rod are not the cause of your problem, then it gets tougher, as you will have to disassemble the engine and check all bearings, including the cam bearings. If you do decide to tear down the engine at some point, pay special attention to the thrust plate at the front of the cam, the oil galley plugs, and the plug at the back of the cam bore. These are known trouble spots. Mike