f115 oil light/alarm on

[Git-R-done]

oil light/alarm comes on while skiing. when idleing it goes off.oil level on full mark on dipstick.stopped using it.pulled it on to trailer and brought it home. what could be going on? what are my first steps? Is it sensor, or oil pump? Is this common?Its a 2000 f115 EFI. Installed pressure gauge on idle it jumps from10 psi to 40 psi. when i rev engine up to 2500-3000 rpm gauge drops to 10-20 psi. it constantly jumps up & down.Worried!!

[boats.net]

Need to check compression and leak down test on engine.