HI Lately my PSD has been losing oil pressure!! My truck is a 2004 PSD CC SB Lariat, It was made in June It has 90,000 miles. I had an edge module but removed it 4000 miles ago. It has an AFE stage1 Magna Force air box, 4 inch Magna Flow exhaust with no Cat., zoo dad mod, dieselsite coolant filter. The needle on my gauge goes to low when my RPMs are low(650rpm) and my check engine light illuminates but as I speed up it goes quicky to normal. It only happens on occasion but last nite it happened several times as I slowed down to make turns my oil pressure would drop to low but as I push on the gas and my Rpms get higher my oil pressure returns to normal quickly.On another occasion when my oil pressure dropped I turned off the truck and restarted it twice and my pressure returned to normal. Today I used my truck several times but everything was ok. During this low oil pressure situation my truck seems to run fine. A little bit of history on the truck: 2500 miles ago it had the FICM replaced and OIL COOLER replaced, 1000 miles ago it had the head gaskets replaced. My truck runs fine except for an annoying exhaust drone that I never had before the Head gasket change. Now 1000 miles later I am having this oil pressure problem. Any ideas? Oh yeah I have not been using the Edge module .Thanks in advance. Oh I am not sure if this an issue but I always run Synthetic oil 15w40 in summer and 5w40 in our cold winters, BUT when the dealership change my Head gaskets they changed the oil and used non synthetic 15w40 .Last nite we used the truck again and once again (once the truck was somewhat warm)as i slowed down to make turns and as my RPMs went to idle (650 RPMs) I LOST oil pressure and check engine lit illuminates . The gauge went to low. As I pulled up to the turn it would hold the oil pressure at 650 RPMs for a few seconds and then drop to low on my gauge. But If I put the truck in neutral I can rev her up, creating Higher RPMs and the oil pressure rises with the RPMs . As soon as I rev past 650 the pressure quickly. I drive further and it happened at all 3 turns. I shut the truck off and oil pressure was normal again and she kept normal oil pressure for rest of my trip. I parked the truck for approx. 5 hours ,started it and did not really let her warm up and drove 10 miles with no issue,Any help would be greatly appreciated, . Thank you and cheers Mike

 

mike as I said you have one of two things going on. to me it sounds like the oil senfding unit though. the other issue I had mentioned does not normally happen at random times. it will drop to 0psi hot idle every time

 

Where would the oil sending unit be located? Whats involved in repairing or changing it? cheers Mike

 

Attached is a file that shows all the major sensor locations.

 

Looks like cheezit is offline - so, your sending unit is next to your oil filter bowl on the front top of the engine. It just screws in. Should be a piece of cake to change it.

 

That looks like a valuable document, but page two is not displaying for me. And that must be where the EOP sensor is shown, because it is not on page one.

Got another link?

 

Thanks for pointing that out. I uploaded the wrong document - names are too close. This one shows both the oil pressure and the oil temperature sensor.

 

It's interesting, I've noticed before and on this document as well, they call that an Oil Pressure Switch. Which is exactly what it is, not a sensor. It is just on or off.

 

I believe the proper term is switch.

It is "on" or "off" based on the amount of pressure being either under or over the amount specified.


A sensor, on the other hand, suggest a more graduated scale and range rather than just two states.

 

Good points on the definition of a switch and a sensor. They are separate and distinct. This switch is listed in Ford's parts catalog as an Oil Pressure Sending Unit with part# F81Z9278AA. The last time I bought one they were about $35.00. I occasionally see them on eBay cheaper.

 

Ford used the proper term of art "sending unit" which can mean either a switch or a sensor.

However, I think all 6.0s are equipped with an oil pressure gauge that reads continuously on a scale.

Therefore, it is not an "on" or "off" device.

The cheaper part is used on cars with the idiot light on the dash.

Bet you Ford used that term so they can put in the cheaper switch if they ever decide to eliminate the oil pressure gauge ... LOL

 

No, we have an idiot gauge, just like all other Fords.

 

The oil pressure instrumentation acts like a switch w/ the "idiot gauge" we have, but IIRC the PCM does see actual pressure values from the sending unit (hopefully a tech can confirm this or set me straight).

FYI -
The oil pressure switch for the gauge activates at 5 psig.

 

I don't think it does. I'm basing that on a study of the schematic. The EOP switch is one of the few sensors that does not feed the PCM. It feeds directly to the instrument cluster. Now it's possible that the cluster relays data to the PCM, but I don't think it does.

Other sensors that feed directly to the cluster include the brake fluid level switch, air filter minder, fuel level sender.

I bet you could unplug your oil pressure switch and the PCM would happily continue to run your engine. Anyone care to try?

I think this confirms it:

 

This would make sense for 2 reasons:

A) It give the fastest / most reliable warning of loss of oil pressure.

Going through the PCM means more risk of signal being filtered / PCM bugs / software errors.

B) It is a legacy subsystem

PCMs were imposed on the old mechanical designs, and some things were deliberately left "as is" or not changed for different reasons, including (A).

C) If oil pressure were to drop, other sensors that the PCM reads will signal trouble (e.g. ICP, coolant temperature) soon enough.


Whether the panel feeds data back to PCM.... theoretically possible.. hmmmm



Is there 2 different sensors?????

i.e. One that is a "idiot light" that indicates loss of oil pressure only

A second one that feeds the oil pressure gauge?