Have an 03 FX4 5.4 with about 260K on it. That said, whenever I use it I glance at the gauges and give a listen just to take stock before setting out with it.
Noticed I suddenly had no oil pressure. Needle didn't move a bit and the light was on. No knock and motor sounded and idled fine. Figured it was the sensor, but could be the pump given the age and miles.
So got a new sensor for about $14 and went to change it. Well, I couldn't get to it very well and being so old (the truck, that is) I figured I was gonna break the connector trying to get it off.
So to check if it really was making oil pressure, first I pulled off the oil filter and drained it. Quite a bit of oil drained out the flange, like what I remember it usually does when doing my oil changes. I put the oil filter back on, topped off the oil and ran it for about 3 minutes. Pulled the oil filter again and it was full of oil and it drained from the flange for a bit, same as before. Right now I'm using a Fram TG2 filter.
Based on this, can I assume the pump is working OK, pressurizing the crankcase and feeding the top end, and it's a faulty sensor? Or should I not drive it at all until I'm able to swap the sensor (I think I can get it when I have more time and can bribe an extra pair of (small) hands), and check the pressure with a gauge for sure?

 

If you don't have valve train noise it's probably the sending unit, if you don't feel comfortable driving it until you change the sensor, then don't. I would use a Motorcraft filter instead of a Fram.

 

The 5.4 uses a siphon type oil pump so you have to use the right oil.5w30 I believe. Otherwise you have a leak around your front cover.

 

Get RID of that Fram filter right now! It's the orange can of death for Ford modular V8's.

5W20 is the specified oil, but 5W30 is okay to use in a 2 valve engine.

 

glc's back.

Yea, if it's not too late for that engine, use the correct filters. Motorcraft, Purolator...

Most orange cans lead to an early grave unfortunately.

Search "Orange Can of Death"