I noticed today after changing oil and filter, I turned the key on and while wait to start light was on, oil pressure came up to normal position(about 40), w/out starting the engine. What's up w/this. Gauge always reads same no matter the rpm or temp.

 

I read on these forums that the stock fuel pressure gauge is actually a computer controlled device, set to run off of a simple switch instead of tracking actual oil pressure. As long as the sending unit sends an OK to the ECM (I think), the computer will adjust the guage based on a program that takes in to account other readings like RPM's, Temp., etc. So, it really doesn't do much for us but say that there is pressure of some sort that meets the minimum requirements of the sending unit switch.

 

....my factory OP gauge stays put until the engine is running, then the pressure registers - I would assume yours SHOULD do the same?
I had an old Ford Ranger that started giving me strange gauge readings, turned out that some vehicles have a device that "conditions" the signal from the various sending units, and goes bad on a regular basis - and yes, that truck showed oil pressure while the engine was off, until I R&R'd this little gem of a device ...(parts store called it a "instrument panel voltage regulator")

 

KISS - Keep it simple stupid!

Change your oil pressure sender...

Then... try other ideas...

I had a OP gauge start dropping out on Mom's 96 and thought that I lost the oil pump or blow the gasket on the filter. Well I never found any oil on the ground. So I changed the oil pressure sender and the problem went away!