OK here goes, I pulles an engine from a 1998 zr2 that was from canada, everything was in metric, after figuring it out it had 75k miles on it, and little over 60 psi of oil pressure, i did the engine swap into my 99 zr2 started it and it reads 10 psi, get it to 4k rpm and it jumps to 20 then but not smoothly, ran it for 30 minutes never knocked or anything and has good flow, and is cooling ect. Where is the pressure sencor located? do i need to change it because of it being from a metric unit? didnt knwo if sensors were different, thanks, also no kincked lines or anything, allready rechanged those and the filter and filter unit in case of clog.

OK here goes, I pulles an engine from a 1998 zr2 that was from canada, everything was in metric, after figuring it out it had 75k miles on it, and little over 60 psi of oil pressure, i did the engine swap into my 99 zr2 started it and it reads 10 psi, get it to 4k rpm and it jumps to 20 then but not smoothly, ran it for 30 minutes never knocked or anything and has good flow, and is cooling ect. Where is the pressure sencor located? do i need to change it because of it being from a metric unit? didnt knwo if sensors were different, thanks, also no kincked lines or anything, allready rechanged those and the filter and filter unit in case of clog.

First thing get a manual oil pressure test gauge on it and check actual pressure.

Where was it when you changed the engine?
4.3 V8 engine?
If so.
Look on back of engine by dist.
Was the oil pressure reading good on old engine?
If so.
Try the oil sending unit that was on your old engine.

Post back how it goes.

I read somewhere that GM has two different oil pressure gauges. One is 0 to 80 and it seems the other is 0 to 60 or something like that . If you are using the sender from one engine type and the gauge from the other that might be your problem.