Well, back to the drawing board. I replaced the upper bearing in the bad journal, as well as the lower bearing halves of all journals. I plastigauged it after swapping them out, and found myself toward the top of the acceptable bearing clearance range (Standard main journal oil clearance 0.019 - 0.035 mm, Maximum journal clearance 0.10 mm). My reading was approximately the 0.038 mark on green plastigage but may have been a little looser than that. It was, however, under the 0.051 mark. Chalking it up to doing the test with reused main studs, I put it back together to see if it had any impact on my oil pressure. I also installed a new oil pickup tube at this time, as well as a K&N oil filter.
Fire it up, 56 psi. Again. Did not break 56 psi for one second, only dropped from there. I shut the car off when the coolant was 174* and the oil was at 16 psi and dropping. Sigh.
So here I am again, asking myself questions. Even if that main journal was trashed, it still plastigauged at a reasonable value. Combine that with the fact that I added lower bearing halves to all of the other, unaffected journals, you would think that I would have seen a higher cold start pressure (even if just for a few seconds) than the same 56 psi I have been seeing. Again, before all of this, I used to see 82psi at cold start up. Now, I make several changes to components that would affect the oil pressure, and I see the same exact number. This takes me back to when I spun a rod bearing on my ms3. I had a bad rattle and low OP and prayed I could replace the bearings and be ok. I replaced them, and even though the crank was trashed, it still made better pressure after the new bearings. They failed again after a few miles of driving, but there was a change.
This is kind of pointing me to oil pump at this point, but I don't know why or how that could have gone bad. I took my old pickup screen and cut it into pieces. It is entirely intact. Nothing should have been able to pass through the pump.
I am running out of options at this point.
