Rotax 912 ULS Low Oil Pressure at High RPM

Do not shim it. It isn't the real pressure. I've seen this several times and it was always been a poor ground connection. The symptoms were all the same. Pressure goes down on rpm increase and back up when rpm drops. When I first experienced this many years ago it took me a couple hours to figure it out. My meter said I had a ground, but I decided  to by-pass the old ground with a temporary good solid ground. Problem solved.

p.s.

If this doesn't fix it and you have a VDO sender replace it.

Don't jump the gun on your lab report either. Just wait until the next oil change to do another. These readings can jump up and down at times for different reasons.

Roger, thanks for your reply.  I've always found your advice to be helpful. 

However, did you see that I said I had connected a mechanical oil pressure gauge as well to verify the reading of the cockpit oil pressure gauge?  Maybe I didn't make that clear but both gauges (mechanical, and the cockpit VDO electric) showed basically the same oil pressure performance including dropping at high rpm.  A ground would not be a factor with the mechanical gauge, right?  It was connected directly to the additional port on the oil pump housing right next to where the sender was connected.

So if the mechanical oil pressure gauge shows a problem, I assumed it was real and not an indication issue, right?  Any further ideas you may have are appreciated.  Thanks.

Since both gauges read the same now it's down to ruling out items that could affect pressure and even temps.

If your mechanical gauge showed the same thing then no, a ground would not be a factor. At this point I would do two things. Install the newer style mushroom looking oil pressure regulator and remove the ball bearing one. Change the spring too. This is a fairly inexpensive and easy change. It will only take about five minutes. See if there is any oil hose that makes a sharp bend that may have a reduced radius that would cause a reduced flow. Flight Design has them (180 degree bend) on the oil hose coming out of the cooler to the oil pump. You can feel the flattened hose under the fire sleeve. I have always placed springs in this hose and flow was certainly increased and temps went down 15F-20F. One last item. You may need to flush out your oil cooler if the install of the new mushroom regulator doesn't work. I have seen this in a few engines. Do these cheap and easy things first and try not to just throw high dollar fixes at it. One thing at a time.

Just a question Rodger has just mentioned all I listed in my first group of questions I asked but in a way more friendly  way. I have one more ask  "Have you recently changed your sprag clutch? As sometimes people pull off the waterpump gear but don't heat it enough and tend to hammer it back. This puts a dome in the oil pump cover plate causing a similar issue .... 

Per your suggestion Roger, I looked (again) for oil line kinks and found a bad one stealthily hiding under some fire sleeve on the line from the oil tank to the oil cooler thermostat.  I've fixed the kink and will purge the oil system once I install the new oil pressure relief valve parts you suggested early next week. 

Attached is a picture.  Pretty kinky, huh?  Thanks again for your help.  I expect I will get a good test next time I try it out.  We'll see...