I just recently got low oil pressure warnings under wot. Pressure at idle is between 20-25 psi hot. When I get up to about 4500 rpm the oil pressure stops climbing at 40 psi. From that point on, the pressure drops slowly as the rpm's increase. At wot I have seen the pressure as low as 20 psi.

I have just changed the oil (15w 50 mobil 1) and filter, there was no sign of metal shavings. On cold starts the pressure will be 40psi and I can rev it up to as much as 60psi.

The pump is a ported ls6 unit. Is the pump going bad or do I have a faulty oil pressure sending unit? I have done several searches on this subject, but can't seem to find anything related to the above symtoms.

 

Start cheap. Change your oil filter, the bypass could be bad.
I would be a cheapo mechanical guage tee it into your sender line and set it on your dash. See if the same symptoms appear.
The fact that you are loosing pressure at WOT high rpm puzzles me. This is not generally a symptom of a bad oil pump, more like a faulty pressure relief valve.

 

I just changed the oil filter and the same symtoms still exist. I will try the mechanical guage to verify the pressure.

 

Try running a heavier weight oil and see if the problem still exists. The same sorta things were happening on my engine but it was built loose for a huge nitrous shot, so u're not gonna get great pressure in that scenario anyways (or if you're getting blow-by).

 

I was running 10w 40 prior to when these symtoms started occuring. I then changed to mobil 1 15w 50 and it increased the pressure a little, but the pressure still starts to drop at wot.

It seems more and more like the pressure relief valve is bleeding off the pressure at wot.

 

....bad pump ...swap it out is my suggestion....