I have a Discovery 98 with a Cummins 275. Last several trips my oil pressure gage pegs out on high. No increase in temp. and engine runs fine. I suspect that the sensor is bad. Contacted cummins by e-mail and basically they said I should contact a dealer....surprise.
The wire from the oil pressure gauge to the sending unit is negative current(ground). The higher the pressure the more ground is sent to the gauge. I would bet you are correct, It most likely is the sending unit. The older units were oil pressure pushing against a spring moving a sliding rheostat. The newer ones are a transducer. The pressure range should be on the side of the sending unit. Available at NAPA
My 98 Overland with the C8.3 Cummins did exactly the same thing. I had a really hard time finding the right part number for the oil pressure sender. Neither Cummins nor Freightliner would admit the part was theirs. They both said that it was installed by the OEM. When we removed the sender and cleaned it with the wire wheel we found it was a Seimens/VDO part. I ended up getting an equivalent replacement from www.egauges.com . None of the local big truck places had anything in stock which cross referenced.
Me, the DW, 2 dogs and more.
1998 Overland Larado, 41', one slide, 325 Cummins, '02 Jeep Liberty Upgrades we've done: SMI-Air Force 1 towed brake system, replaced all 3 TVs with new hiDef LCDs, inst. Xantrex 2Kw Inverter, Prog. Ind. HW50 surge protector
I also have a problem with my sending unit. It needs to be changed by someone that can reprogram as it goes from one wire to two wires or something like that.
I had the gage changed but that did no help. Mine goes to 0 on starting but the red light goes off so I know there is pressure there. I turn off engine and restart and it is ok.
AeroP
Same problems on mine. Bought a sender from NAPA for around $50, fixed problem. I first installed a temp. mechanical gauge to be sure, I'd say just replace sender. Bob
Mine was two wire, one for gauge, one for oil light. Made by VDO
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