Actually you want the oil pressure to fluctuate because at 700 rpm it's at 40 psi but as you're engine gains speed, you're oil will circulate faster to compensate and lubricate the moving parts. So really you want that needle to move as you're engine gains speed and goes back down to idle. It shows what oil pressure you have at any given point while the engine is running

 

Normal Jeep 4.0l oil pressures are 10-30 psi at warm idle and 35-55 psi at 50 mph. If the oil pressure really concerns you, check it with a mechanical oil pressure gauge. Cheap Chinese oil pressures senders have spotty quality. It is best to use genuine Jeep sensors. Check the oil pressure sender wire plug and wire harness for corrosion or damage.

 

Try Napa oil pressure sending unit, cheap and easy, make sure you get 2 wire for the gauge. Bought my first from Unadvanced Auto they insisted was correct, not.

 

My 97 XJ was doing the same thing when I got it. I changed the oil, filter, and sensor to no avail. I finally found a write up on here about how oil deposits get built up at the hole where the oil pressure sensor threads into the oil filter housing. This blockage of oil flow to the sensor causes the sensor to read all over the place. I wouldn't recommend trying either of these things until you have changed the sensor and oil and checked all wiring and connections. This can be costly and messy if you do it wrong. That being said, there are two remedies to this problem. They come in varying degrees of difficulty and cost. They are as stated:

1. Remove oil sensor, install small hose into hole, place end of hose in catch can with at least a quart of space, start jeep for a few seconds (5 at most!) This method blows what ever debris may be there out in a hurry but be careful because you're going to lose a lot of oil and fast. Don't let the engine idle more than 5 seconds and don't touch the gas. Remember to top off your oil when you are done!

2. Buy and replace filter housing. This way is probably safest but will cost more in time and money. You might as well do another oil change with this method.

I used method 1. I believe I revved mine to 2500 or something but afterwords decided it was unnecessary. I just lost more oil than I needed to and had a big mess to clean (it blew my hose off). I recommend just letting it idle a few seconds. It will do the trick just fine. Snoop around on here a bit more and you should be able to find the thread I read about this in. Hope this helps, good luck!

 

Thanks for the tips. Gonna get on it shortly.

 

every jeep I have ever had does this my 97 is all over Ive replaced the sensor several times it works good for a little while then starts acting up again. I just picked up a mechanical gauge to put in.

 

I picked up an oil pressure test kit and all is within spec, i also cleaned out the filter housing as recommended and bought a better switch from Jeep. Running fine now. Thanks all for the tips!