ok guys need some help with this one.
I have just recently put a s5 na motor with the s5 intake in my 88 s4 vert.
got it running running yesterday and noticed that when I give it gas and hold it at 4000 rpms that the oil pressure goes up to what looks like to be a normal rate and then it starts to slowly fall back down while hold the pedal down at 4000 rpms.

There isnt any oil leak externally.
Im also using the s5 oil pressure censor and running a stock ecu and ive checked the oil level as well and it good.
also this s5 motor was rebuilt before i bought it and the oil system was sealed before I put it in my s4 vert. I never opened up the oil system at all.
I keep the front timing cover and water pump from the s5 and used a block off plate for the omp.

 

The sending unit is bad, replace it.

 

hope so. Ill try swaping out that one for one i know works that i have laying around
(wiping swaet from my forehead)
hope this works.