High Oil Pressure - '99 TJ with 99k miles

Hello All, I have a 99 TJ sport with about 99k miles on it. The engine oil pressure two days ago pegged itself at 80psi on the gauge and has
stayed there. It normally sits between 40-60psi when driving and below that when idling. The oil has been changed every 4-5000 miles, there is no knocking and the engine sounds fine. I did an oil change this morning and the oil was practically pristine so I'm some what confused. Also when I turn my key in the ignition before cranking the engine the oil pressure gauge goes to 50 without the engine running. I also went on a drive yesterday (100miles) and after about an hour of driving the oil pressure at idle would go down to about 60-70. I have heard these little oil gauges are notorious for crapping out so I'm wondering where to start. I have checked for oil leaks since high pressure blows a gasket and there are none. I don't own a pressure testing kit and the only ones I have found are $100-150 so that's out. I don't have the money to throw parts at it at the moment and it is my daily driver so how can I diagnose this issue? Where would I start? Should I actually take it to a shop for a check?
Thank you for any advice/help ahead of time, -Stephen
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Start by replacing the oil pressure sending unit, which is relatively inxpensive and easy to swap out.
With that known OK, it's time to swap out the guage internals. If you're getting a reading of 50 when the engine is off, and the sending unit is known good, it's time to swap this out.
If it's working at all (needle moves), place your bets on the sending unit.
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Cool, thank you for the advice. Since the pressure sensor is not the same place as my old jeep. The manual i have is a tad outta date 1987. Which manual would anybody suggest? Haynes/Chilton some other?
The Dealership one is $130 so thats out.
Thanks Again, -Stephen

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Get the one from the dealer. Its the best! It is availble out there on CD I think. -jenn

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snipped-for-privacy@gmail.com wrote:

If you don't want it to replace it every few years, buy the OEM item. I've discovered this the hard way. Most aftermarket parts are junk.
I thought of something else that may help you. If you disconnect the wire from the sending unit and your guage reads zero before/after starting, you can be even more sure it's the sending unit. Try this before replacing anything.
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wrote:

I sort of agree, but I haven't had your experience. Car manufacturers don't *make* cars - they pretty much just assemble them. (While this is possibly not true for engines, it is true for practically everything else, especially sensors). You *can* buy a quality aftermarket item made by someone whose name you recognise.
Dave
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You're talking about the manual, right, not the pressure sensor?
That's about the going rate for the manual. But IMHO well worth it. No guesswork like you would a Haynes or Chiltons.
wrote:

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Oil pressure sending unit. They seem to go out frequently. I've replaced the one on my 98 3-4 times now. Pegged high is a normal symptom for this, or pegged low too. -jenn

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If the wire to the sending unit is shorted to ground it will peg on 80 psi.
You can rent a mechanical gauge, often at no cost, from many auto parts stores.
You should check the actual pressure with a mechanical gauge before you start replacing parts willy-nilly.

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FWIW, there is a gauge check routine. My '97 FSM says put the key in OFF position. Press and hold odometer reset button. Turn key to ON (not START). Release odometer reset button. Guages should all move through their ranges.

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