I have a 383 SBC (block is from a '94 Suburban). This engine has less than 500 miles on it. Last weekend I noticed that on moderate acceleration (between 2500-3500 RPM) my oil pressure drops to about 10-12 psi. I changed the oil and filter, but this did not resolve the issue. I took a few videos to show what's happening.

The oil pressure gauge isn't quite accurate. The sender is down by the oil filter, for sake of simplicity I connected a mechanical gauge to the oil port at the rear of the block (by the distributor) and I have similar results. Sorry about the sun glare.

When I got back to the house, I sat in Park and brought the RPM up, but it held pressure in Park/Neutral.

The oil pump is a Melling 10552 pump (only 10% increased volume, not the 25% increase HV pump) with Canton bolt on pickup to match the Canton oil pan and Melling pump. There is 3/8" clearance from pickup to pan. If I give it more throttle the pressure will rise about 10 psi or so. When I changed the oil and filter I cut the Wix filter open and found small bits of blue rubber in it. I can only guess that this may be part of the FelPro one piece oil pan gasket and that perhaps it has contacted the crank and got tore up on the inside.
My next step (I think) is to pull the pan and do some visual inspections. Before I go that deep am I overlooking anything else? A friend says I need to check crank end play, so I will get that measurement as well. When cruising the oil pressure stays around 40-45 psi, this seems to begin to drop when I accelerate moderately and maintain that RPM range. As soon as I let off or give it more throttle, the pressure rises.
Any ideas?

 

Crankshaft end play is .010", a little high for a fresh engine build , but I still don't see/understand how there would be any correlation between end play and oil pressure.

 

Did the pump pickup get secured in place, or is it possibly loosening/sucking air?

 

Oil pump pickup fell off, loose or installed to high off the floor, low oil level in the pan.

 

There are 2 bolts that hold the pickup to the pump inlet, with a 3rd bolt that goes through a support bracket (one of the pump body, bottom plate bolts). It was 6 months ago, but I am pretty sure that I used loctite on the threads because I didn't want them to come loose.

 

Maybe you have a partially blocked oil port on the china wall of the block from some of that blue rubber. If you have a pre oiler, I would pull the distributor and use the pre oiler and see if you can replicate the problem. If it does, I would then drain the oil and look at it to see whats all in there. Then if need be pull the pan.

 

Because of the rapid increase in thrust wear, I replaced the main bearings. I found no mechanical cause for the loss of oil pressure. Other than the thrust wear, the bearings looked fine. I modified the upper thrust bearing to direct feed the rear thrust face and put it all back together. This time with only 5.5 qts of oil instead of the 6.5 qts I was running. I don't have the oil pressure problem anymore.