So I have a 2002 Expedition EB with the 5.4 with a little over 355,000 miles (ye s I know that's allot) We purchased it at 230,000 and was fleet owned and maintained before that. It had given us 20,000 miles of trouble free use, from long vacation trips to 200 mile trips pulling 5,000 lbs. But let's get to the problem... Recently went down the interstate, all of a sudden check engine light comes on, oil pressure drops, engine starts shaking/knocking. Get it to a shop, they look at it, change oil, and wasn't for sure but figured engine was maybe a gonner. Tow it home, and when you crank it, starts out fine and oil pressure on dash is good, then after a few seconds drops down, then goes back up and eventually stays up and truck will run fine besides a light knocking sound. Not for sure what is wrong, figured maybe oil pump, but figured motor would have blown already. I seen something about a oil sending unit, could that be the culprit? I have no idea, and with that many miles it could probably be numerous things that failed. Thanks in advance

 

A failing oil pressure sensor can make the gauge fluctuate or drop to zero, but it wont make the engine run poorly.

You need to get a mechanical oil pressure gauge installed temporarily so you can monitor the actual oil pressure at cold and hot. From there you might get a clue on which direction to go.

Sometimes a bad oil pump can mimic the symptoms of a worn out engine, so without tearing into the bearings it could be tough to figure out what's wrong.

Ar that mileage , it could just be worn our. But with that said, those 2v 5.4's have gone over 1.2 million miles before they are shot, so it depends on maintenance and how it got used previously.

 

And don't rely on the oil pressure gauge in the dash, it's not a real oil pressure gauge. It's just a glorified "low oil pressure" lamp. It only has two readings - "normal" and "low", nothing else. The "sensor" in the block is actually just an oil pressure switch which only has two states, on or off. If your gauge is fluctuating between "normal" and "low", it means either that the switch or wiring to the switch is bad, or that the oil pressure is so low that it barely makes the pressure switch turn on. If it's the latter, then it could be either low on oil or something clogged, such as oil pickup tube, filter or oil channels. Other causes for low oil pressure is a failing oil pump, or worn out journals or main bearings, which basically means the engine is worn out.

 

Sounds like a spun main or rod bearing.