Update: 2000 Jeep Wrangler. I went off roading & the entire engine interior was caked with mud. I immediately started getting a low oil pressure reading on my dash. I figured it was the sending unit, but it doesn't make sense that the sending unit would partially work. When RPM's go up the oil pressure will rise slightly. Also I switched to a higher viscosity oil and there was a slight difference in reading. This leads me to believe it's not the sending unit and it's more likely the oil pump. Any ideas?

More common for the sending unit to go bad on our TJ's versus the actual pump, especially if there is no drivability issues or engine noise.

I would replace the sending unit but go with an OEM Mopar unit.

How low is it reading at temp when idling? It is normal for the pressure to dip after it gets up to temp and not under load, i.e. cruising along. The oil will get "thinner" as it heats up and when you are idling (like at a stop light) the pump is running at a lower speed than when driving (doing 30, 40, 50 mph down the road).
First time I saw it happen I freaked until I talked to some people and found that it is normal. You never really pay too much attention to the OPG unless you get a check gauges or CEL.

What oil pressures are you seeing on the gauge? It is normal for oil pressure to drop a bit once the oil has warmed up, and it is normal for the oil pressure to rise and fall in sync with the engine RPMs.

Funny you say this Jerry, even after my response I have noticed something very weird today on the way to work.

I changed the oil and sending unit yesterday, oil since it was due and sender since I started getting some odd readings as I was driving. (could be doing 60 and the gauge would drop to zero and CEL came on then go right back up to over 40). Driving in I was about 20 minutes into my trip and noticed that when I would slow down from 65/70 to 40 the needle would drop to what I would guess is 10 and as I would accelerate back to speed the pressure would go up. Never noticed this before. I have seen where after driving I would come to a stop light and it would drop down like that but not just when slowing down.

Engine is new and only has 12k miles on it so I am hoping it is not the rings, I know the pump does not make the pressure it just circulates the oil. If it is the rings I can take it back to the mech and have him fix it under warranty. I am leaning toward possibly faulty sender or gauge. Am going to hook up my reader and see if I can get real time data.

Any thoughts?

I don't think I've ever noticed my oil pressure rising and dropping, just FYI.

Oil pressure is supposed to rise and fall in step with engine rpms since the oil pump is engine driven. 10 psi per thousand engine rpms is a good rule of thumb for acceptable oil pressure.

Older TJ oil pressure gauges will show the pressure fairly accurately. The factory reprogrammed the oil pressure gauges of newer TJs so as to not show the real ups and downs of the oil pressure since it was alarming new Jeep owners who had never had an oil pressure gauge before.

Some of the newer sports cars went to gauge controlled by just a pressure switch and when owners complained they programmed in a rpm dependent needle movement that was still just based on a pressure switch with the fluctuation all made up my the computer

Any real analog gauge directly tied to mechanical pressure or a real analog transducer will fluctuate both with rpm and oil temp

But now that all the gauges read off a bus signal from PCM it is whatever they program PCM to sent the gauge

Per FSM, idle oil pressure for both 4cyl/6cyl is 13psi.

If it were the rings I think you would be burning oil. A blue cloud of smoke would be following you. When Mine is warmed up I have about 20psi on the gauge and it rises and falls with the engine rpms.

Rings affect compression and burning crankcase oil but not oil pressure

Assuming adequate oil level bad pressure could not be a ring issue as pressurized oil not sent to rings

Pressure is pump or pickup or bearing ect but not rings

However if suspect low pressure best to verify with mechanical gauge