[chiphead]

Cut the oil filter open first. If there is no metal in the filter pleats, this is a good sign. Usually if an engine is going away, the shredded bearing material gets trapped in the oil filter pleats. I cut my filters, and have a tool for doing it, kind of looks like a big can opener.

No metal in filter means either the checkball in the pump is stuck or maybe the engine was built with very loose clearances. I had this happen with my current 400. I had done a cam change, and then shortly after the oil pressure was like 10 PSI at idle, no higher than 35 PSI at 2500 RPM cruise. I guessed the ball was hung up, so I gave the engine 2 or 3 good revvs and shut it off. The next time, magically it had the proper oil pressure again. I then cut the filter open and found a wadded up piece of masking tape. I had used blue painters tape as a pattern to clearance the valley pan to fit the intake. A piece of blue masking tape got hung up in the ball and bled off a bunch of oil pressure. A few revvs blew the tape from under the ball and it was all good.

The other thing that is likely, is the shop built the engine with very loose clearances. Pontiacs have very big main and rod bearings (compared to other makes), and if you set the clearances loose, the oil pump has trouble keeping up. There is no high volume pump for Pontiac, like there is for chevy. And if the shop set the engine up like a performance BBC, (greater than .001 per inch of journal) it's going to struggle to maintain pressure. A BBC has a 2.75" main journal, a Poncho 455 is 3.25".

*edit* Does the engine have valvetrain noise? The shop could have used chevy lifters, which have the oil band in the wrong place vs a Pontiac. That would bleed off oil pressure.