Ok first let me say I tried a search but server was overloaded so I decided to try a post. I have a 86 b2 with a 2.9 replacement jasper engine with 50k on it. It was giving me no trouble until I tried to start it after letting it set for a month or so, It started right up no troubles then started clattering like the lifters werent getting any oil then got worse so I checked the aftermarket gauge that I installed after the original engine shot craps and it had dropped to like 5 psi so I shut it off. Started it up again it ran for about 3 min and oil pressure dropped. So I pulled the valve covers thinking that the oil valleys clogged but they looked good other than the pass side was a little tarry looking for lack of better word. I then ran some sea foam thru the engine thinking that the oil screen is clogged it seemed like after I changed the oil that had fixed it but after about 10 min run time it starts up again. here is the sceniro I start it it runs good at about 40 psi then after awhile not when engine is warm it starts to drop and If I hit the throttle and rev the rpm the pressure drops quicker then after the rpm slows down it goes back up but not as high as it was before then rev it again it drops farther then levels out lower then before until lifters clatter then I shut it off. let it set then it will do the same thing.. Is there anything in the oil pump that could be slipping or by- pass type pressure regulator that could cause this? Oh and my son says he hears what sounds like to him a electric fuel pump running {only louder} running down by the oil pan. any chance a gear on distrubutar is slipping or something like that? Sorry for the long post.
Thanks for your time

 

I would suspect a pump issue or a cam bearing problem but the gear could be it too, the only way to know is to pull it out and take a look.

 

pull out the distibutor or pull out the oil pump? Do you have to pull the engine or can you just un do the motor mounts and raise the engine a bit?

 

If it's a 2wd they say you can get to the pump without pulling the engine but from what I've heard it's easier to pull the engine out, 4wd requires removal.