3.8l oil gauge shows flickering oil pressure.

i have been putting a salvage engine in a 96 stang and got it running yesterday and the oil pressure gauge is flickering from 0-3/4 it only shows 0 at idle or under 1,500rpm sometimes, it will drop every minute for 30 seconds or so and jump back up very very rapidly and it falls rapidly also.

i really thought it was a sending unit or gauge/connection issue. so cleaned the connections and it didn't change and then i just let it idle when it showed 0 and listened for engine noise (instead of revving it and getting oil pressure back) after about 30 seconds of no pressure the lifters started ticking and i revved it the gauge showed pressure and the engine got quite and purred.


ruled out
-determined the gauge is reading correctly
-swapped out filters already
-oil is fresh

possibilities
-oil pump pressure relief valve is bad
-the sump is clogged, lamberts salvage put a new pan on it because the original one was cracked.

any other ideas?

I'd say bad motor, cam bearings? clogged screan? these motors suck period. If its not oil problems its head gaskets.