1990 f-350 w/351m. loose oil press after runs short time. r&r'd new oil pmp & p.u. screen ttl clean short time ago. wen press drops, lftrs clack. any ideas b4 I drop pan again. thnx 4 ur help --- Ed.

Why are you running 10 - 40 weight oil. You might want to rethink this. As the miles go up the ware on parts goes up. So I would recommend a 5 - 20 or 5 - 30 high mileage oil. If the oil pump is that new and working properly then this will help with the pressure.

A failing oil pump.. but more likely a clogged pickup tube or screen.. can cause this once you get above a certain rpm..the pump can't keep up with demand so to speak. .

Drop the pan..clean the pan..inspect for solids etc.. .. remove the pickup tube/screen.. clean or replace the pickup tube and screen..those parts are generally pretty inexpensive.

Of course it could be the sending unit.. or a bad ground/short.. yet depending on how well the rig has been maintained..or operating environment.. sludge and solids blocking the pickup tube and screen could be the culprit.

It would never hurt to drain and drop the pan.. new gasket.. new pickup tube and screen..clean the pan.. new filter.. new fresh oil.. some recommend sea foam... just follow the directions.

Best of luck!

check the battery terminals. it could be loose or salt formed. if salted pour some hot water on it or tighten the connections

It sounds like you have a valve or rocker issue, I would run an engine cleaner through the engine. I suggest draining 1 quart of oil, pour in the cleaner and run engine for 5 min. Let engine cool and drain the oil. Pretty much another oil change. This will hopefully clean a sticking valve if this is the issue. But I also would check for anything hitting the pulley's or fans that may have came loose. I've seen this a lot. Good Luck. It may take 2 cleanings for the engine, so don't get disappointed.

There may be an excess of sludge blocking the oil pump strainer. This same thing happened to me a couple of years ago. I bought a salvaged 95 Dakota that had been in a flood. The seller may have ran an oil flushing product in the engine which frees oil resides in the motor. However, the product states that the oil pan and pump screen may need to be removed and cleaned in high mileage motors. At the time my motor only had @ 40K on it. I also used the flush trying to clean the motor but it got worse.
Bottom line drop oil pan and clean the pump screen.
Remember, some oils have parifin (wax) in them so use a wire brush and parts cleaner on the screen.
Your problem could also be an engine idle speed problem or electrical so tune the engine and check engine codes before dropping the pan. But do it soon because if it is the screen then it could become completely clogged at any time.
AR in NE

you could have sludge in the crankcase that is blocking the intake screen for the oil pump ... that happens a lot if oil isnt changed regularly .. in some cars it happens even if you do. ...the clatter you hear is the valve lifters collapsing . they need oil pressure to keep them extended properly ... if your oil pump isnt bad it soon will be .. it needs lub also or it will quickly be damaged ...sometimes you can wash out the sludge with kero/oil mix but the safe thing to do is drop the pan .. clean up the sludge and replace the oil pump.while you are there ...once you have the pump working you can first run cheap oil to clean out things ..then drain and install synthetic ...that will do a better job of cleaning out remaining sludge ... of course make sure you have the proper amount of oil to start with .. make sure there is no water in the oil (milky oil) .. make sure oil filter is not clogged ...some oil filters have a one way valve ... that can stick if the car isnt run for a long time .. ....

Could be low on compression, or torque converter may be slipping

If its a rapid clack time then it could be the battery terminals need to be cleaned, it could also be the starter solenoid mounted on the fire wall has loose nuts corroded or the ignition wire from the key switch the round connector can wear out and not make contact. So check those things first if you have a test light I can give you the procedure to test the cables and solenoid.

if you are finding shavings after this many miles i would suugest a crank kit and oilpump the bearings are worn out

Check if fuel or spark problem,..all engines need both to run...use starting fluid in air intake ,..if it runs very shortly-fuel pmp?,,ck for spark at spark plug,work your way back..also ck timing belt-intact? Kev-MN