This is a bit odd and kinda opposite the way oil pressure gauges and/or sending units goof up but mine reads off the scale while underway. After warmed up it will read about 20 psi at idle and will peg out as soon as you come off idle.
1.) Is this a common issue w/XJ's?
2.) My first thought is to replace the sending unit.
*No, I haven't connected a mechanical gauge to it.....yet.
Really I'm wondering if there are issues with the OEM gauges.
I believe I have a similar issue/question, My 99 Sport with 174,000 decided to idle at around 40psi of oil pressure and goes up to nearly 80 psi while highway cruising. Seems to be running fine, but, the oil pressure seems way high. It used to run in the 40-50 range. What is up with this??
My '93 XJ County had the same problem. I nearly messed my shorts the first time the gauge pegged. It took me about 5 minutes to figure out that every time I changed my oil filter and ended up hitting the sender that I was ruining the wires. I never did get around to fixing it when I sold it at 200k.
failsafe feature. a dead gauge or bad ground always pegs the needle.
according to factory manual, disconnect wire, and gauge will peg. reconnect and it will go to zero with ignition on/no running condition; if gauge is ok.
they have been known to temporarily peg when starting a previously warmed up motor on a hot day, but as soon as idle is established, gauge should go to around 20 psi or so. rule of thumb: 10 psi per 1000 rpm.
I replaced the sending unit ($23 @ O'Rielly's) and that fixed the problem. While I was at it, I tie-wrapped the wire (and wiring loom) to the mounting bracket for the oil dipstick to keep it out of the way of the filter.
They can cause the oil pressure gauge to be inaccurate. And they can leak oil. Short of falling out and becoming a road hazard, that's the extent of the problems that a "bad" oil pressue sender can cause.
yeah, tell me now. mine blew off after an oil change. i look down and the guage reads full, i look up and see smoke coming up my windshield..i pull over immediately to find the sender dangling over the starter.
new unit and more oil and its fine....until last weekend when it died.