I've been having an itermittent problem where oil pressure idiot gauge and idiot light go to the nogood setting, usually for a second or two and then pop back to good setting.

I was thinking it may be just a clogged pressure switch but then last night both gauge and light went to nogood and stayed there and almost immediately the engine started making knocking noises. It continued this way for a couple of miles and then I shut it off. The engine noise seems to indicate it's not just the gauge/pressure switch.

Now this morning, it's back to the more usual symptom of running and sounding normal and the gauge and light dropping to nogood for a second or two every couple of minutes.

My probably dumb question - is there something that can stick intermittently and cause the oil pressure to drop out and then come back when it unsticks? I read somewhere about a bypass spring in the oil pump. Because it seems like the oil pressure really does drop out at times based on the engine noise and then comes back and it's not a gradual thing - it's either okay or really gone.

Background:
'97 Expedition with 4.6L
120K miles
Sludged-up engine (my fault)
Oil currently in engine is 5W30
Several oil changes recently to try to clean it out a bit
Peps Boys put a mechanical gauge on it for about a half hour and it showed about 10PSI at idle and about 20PSI when reved to about 2500. Pressure never dropped out totally during this half hour.
Oil pressure switch replaced after problem started with no affect.

Any advice would be greatly appreciated.

 

I would bet there is a loose connection, either the gauge end ore the sender end. Your oil pressure is ok, They say 10psi for every 1000 RPM.

 

That's what I was thinking also... but last night there were serious engine noises that started just a couple of seconds after the gauge dropped to nogood. Then this morning when the gauge reads okay the noise is gone.

 

I just dropped it off at the dealer. Service rep said maybe the oil pan has enough sludge in it that the oil pickup can sometimes pull some sludge and get clogged up and then when you shut it off the sludge settles and it's okay again.

They're going to check pressure with a real gauge and he suggested maybe what they should do is pull the pan and clean it out for about $200.

 

On My 460, I am able to look up at the pickup screen thru the drain plug hole with a flashlight. I check the screen every time I change the oil.

 

How did you sludge up the engine, using different types of oil or prolonging oil changes?

 

I sludged-up the engine by general lack of attention. I didn't change the oil very often and when I did I used whatever weight and brand the oil-changer generally used. Sorry, I'm sure these are blasphemous words in this forum but maybe my confession will cleanse my soul if not my engine.

 

Your confession will free you from your sins. Just keep the oil and filter changed every 3000 miles from now on and you will be rewarded with a longer lasting engine.
Jimmy

 

I'm seeing a very similar situation with a 2001 5.4 50k 5-30 Mobil One changed fairly often -avg 5k
For no apparent reason several times now the oil pressure has dropped to nothing, according to the gauge, and oil light came on.
In what seems like forever (a few seconds) it goes back to normal. Happens only in town usually cold. No 'bad' engine noise however.
Will add a good mech gauge this weekend and see what is really going on. Suspect faulty sender or wiring.

 

Welcome to the forum badgerc.
If there are no engine noises, I would suspect the sending unit first. Mechanical gauges don't lie, so you should know for sure after you check it.

Jimmy

 

This goes on so long I'll only put in the high points. 1999 Expedition 5.4L, 73k, Mobile 1 every 5k. Going down road and oil pressure dropped to nothing and engine stalled. Restarted and ran as everyting fine. Approx. 4 miles later same thing happened. Had towed to Ford dealer and they didn't find anything wrong and so replaced the IAC and said the oil pressure sending was bad. I declined to have the Oil pressure sending unit replaced. On the way from the dealership oil pressure light came on again and engine locked up when I ignored light and guage. Had towed back to dealer and they found a laundry list of possible problems including bent valves, burnt valves, cracked head, no compression on 3 cylinders, etc., as engine would hardly run. They wanted to tear down engine at my expense. I had taken to an independent garage and they found oil pressure does drop out and not sending unit. Engine floods and runs runs lean at same time. To be continued.

 

Continued... Oil diluted with fuel to viscosity of water. Replaced injectors, sensors oiled cylinders to get compression back up. Engine just ran horribly and oil pressure drops to 0 in couple of minutes after starting. Ford and dealership ignore me and my attorney. I Had another shop replace the complete engine with new fuel rails, coils etc., same symptoms but has oil pressure and no engine codes. Two shops have given up working on. I'm going to replace the PCM next. I hope eventually the dealer will eat the old engine as it is fully intact. Reimburse my expenses and loss of use for over a year. All this from a faulty oil sending unit!

 

I'm having a similar problem with a 98 navi 5.4l 4x4 does anyone know where the oil sending unit is located on this vehicle?

 

The oil pressure sending unit is located at the lower left (driver's side) corner of the engine, near the oil filter.

I have the same problem on my '00 Exp 5.4L Although no noise when the oil pressure light comes on. Seems to immediately go back to normal with a light rev of the engine. It may do this four or five times until the engine warms up. Once the engine is up to temp the O.P. light stay out. I am planning to replace the O.P. sending unit.

 

I located the unit and replaced it over the weekend. It was just above the front transfer case. The problem still is there. I'm assuming there is some sludge in the oil pan the the pump is picking up and causing it to drop pressure. Would anybody know if there is any problems with pulling off the oil pan and cleaning it out?

Thank You
Michael