Erratic oil pressure

[Ethan92GSX]

Alright so I have the strangest problem. I just finished putting my car back together after building the motor and everything runs and sounds great except my oil pressure is all over the place. At idle on a cold start it will be a little jumpy around 20psi then all of the sudden jump to 80psi and bounce between 20-80 very quickly and randomly. When i'm cruising the pressure goes to about 40-80 but it still jumps around very quickly. This is on an aftermarket mechanical gauge and I have also hooked up another gauge to the head and it is doing the same thing. The stock one isn't jumpy but it does wander all over the place. Anyone have any ideas what would cause this? I'm thinking air is being pulled into the oil pump through the sump or the oil housing somewhere.

This video kinda shows the same problem i'm having except mine jumps around 30-50psi not 5psi, and its never steady.

Strange oil pressure behavior - YouTube

 

[Mickey6]

Sounds like a bad oil pump. Best guess for the oil pressure being all over the place is cavitation, you wouldn't have any air getting in b/c its a pressurized system. Did you replace the front cover with a new water and oil pump?