I had a problem develop today on my 98-24V (It's a Freightliner XC chassis diesel pusher motorhome, 5.9, 275hp with Allison 6-speed auto) With 70K miles.

While at idle, the oil pressure gauge indicated normally. When the throttle was blipped, the gauge immediately went off the scale. (Freightliner uses Ford gauges, an "L" and "H" and a middle range with "normal", no actual pressure numbers) The engine had just bumped less than 100rpm off idle when the gauge jumps to the end just past the "peg" marker, but there is no post for the needle to hit. The needle goes to exactly the same spot each time, no further, no less.
I drove it 20 miles or so and everything seems fine. I had to drive it to the storage lot a couple hours after the problem first started When I restarted the engine, the needle went to it's "pegged" position and stayed there. It did not return to the lower part of the gauge on idle like it did earlier in the day.

Oil level is normal, coolant level is normal. Oil was changed a couple months ago. No lights went off on the dash to indicate this condition.
Does this sound like the oil pressure sensor or switch? Anyone else had this issue? Any suggestions on troubleshooting?

Thanks.

 

Sounds like either the sensor is bad or the gauge is bad. Probably could be checked with a multimeter.

 

I once had the oil pressure regulator stick and cause abnormally high pressures. Had to replace the plunger in the regulator. These oil pumps are very high output pumps and a malfunctioning oil pressure regulator will cause higher pressures on this engine than on other engines.

 

I visually checked for loose connections or shorted wires today. Didn't see anything wrong. Tried starting it, the needle for oil pressure reset with the rest of the gauges, but a couple seconds after the engine started, the needle pegged at the end. I think i'm going to try changing out the sensor first, if that doesn't work, then i'll try checking the regulator.

 

What you SHOULD be doing is hooking up a mechanical oil pressure gauge and finding out what the actual pressure is.

 

I called Freightliner service today. They told me nothing in the engine could cause that high of pressure on the ISB and that the problem is probably the oil pressure sensor or the wires to the sensor. If the pressure was really high, I would expect to see a distorted oil filter, or some oil leaks around the filter.
Calling around for the oil pressure sensor part today, called 2 Dodge dealerships. Both told me it was $306 for the part. Ended up calling Freightliner (expecting a much higher price) and the price was $40CDN. So either something is drastically different on the dodge trucks, or both dealerships didn't know what they were talking about.

 

Cummins now supplies a oil pressure switch instead of a sensor and they supply a harness too and, together, they add up to 40$Cdn. The Switch is either ON or OFF instead of the varying output of the sensor. The bad news is that your ECM has to be reprogrammed with the Cummins Insite Scan tool so that the ECM recognizes the on-off signals. All this is explained in the instruction sheet that comes with the switch.

 

On my Freightliner the oil pressure sensor is only used for the Engine Protection System. The oil pressure gauge on the dash is mechanical and they have run a hose from the engine to the dash to operate the gauge.

 

I picked up the part from Freightliner tonight, it's nice that their service and parts departments are open 24/7.

The pressure sensor isn't mounted in the block like I would have expected, it's on top of the oil filter which is mounted high up on the engine, beside the valve cover. I will change it tomorrow and hopefully it solves the problem.

 

Did you get a switch(one terminal) or a sensor(three terminals)?

Let us know how things work out after you change the sensor.

 

I changed the part and oil pressure back to normal. I attached some photo's of the oil pressure sensor, it screws into the oil filter housing and has one wire that goes to the terminal marked "G".

Thanks for the help.