My 2004 5.4 has about 275K miles on it. Once in a while the low oil pressure warning buzzer comes on. Always while I'm stopped at a red light. I accelerate, buzzer goes off. Might not here it again for weeks or months. The oil pan is full to stick mark.
Is the pump failing? I just had the gage cluster rebuilt.
Is the pump within the pan? Should I go with a stock pump or one for a high mileage engine?
Thanks for your help.

 

Most likely the oil pump sensor is faulty. Easy fix to just replace the sensor. Best if you could put a mechanical gauge on it to confirm.

 

Please report back your oil pressures at:
1. Cold start idle
2. running temp. idle
3. cold driving 15-2500k
4. warmed up 15-2000k (freeway rpms)
I suspect you are seeing normal wear & tear lower pressures.
What oil viscosity are you using
Any idea on oil consumption

 

I'd lean toward the oil pressure sending unit. They tend to leak up into the connector and cause erratic pressure readings. I'm on the 3rd in my 2007.

If you change the oil pressure sending unit and still have the problem, the o-ring in the pickup tube may be no good causing air to be drawn in. Also a common issue.

This can also be caused by excessively old oil or skipping a filter change when changing the oil.