Unusual Oil pressure issue

I've got an unusual oil pressure issue. Unlike some of the other posts here, my oil pressure seems to have gone higher. Recently purchased a 2000 Cherokee with 82K on it and everything was fine with oil pressure showing between 20 and 50 lbs when fully warmed up depending if being driven or at idle. One morning, went to start it and the check engine light came on and the gauge was reporting 0 pressure. After shutting it off, and restarting it, the check engine light went out, but now the oil pressure gauge reports between 40 and 50 lbs of pressure at all times. I've replaced the pressure sending unit, but no difference. Currently, I'm waiting on a Oil pressure testing kit i've ordered to show up so I can finally see if I should be worried or not. Just wondered if anyone else has had this experience or if I'm in uncharted territory.

did you take the valve cover off to make sure it is still sending oil. this make a mess, but is a really good way to ease your mind about the oil pump. and it's cheaper than waiting to long.

You said it reports 40-50 at "all times"... i assume you mean when the motor is actually on right? If it says that when the engine is off its not the motor. How recently have you done an oil change, what filter do you use, and what weight oil do u use? Many oil filters will net you around 13-30lbs at idle but the ford FL 300 oil filter nets me 50lbs at idle. 50lbs at idle would be a good thing as long as its not due to an obstruction downstream.

fyi, another thing thats common to go bad in the 97+'s is the connector that connects the gauge cluster to the wiring. It gets corroded and the wires lose signal conduction as I understand it. i haven't had this issue in my 2000 but something to be aware of for future reference if your gauges start acting wierd.

Sorry for the misinformation. Yes, the pressure readings are when the engine is running at idle. Also, I didn't mention it, but I replaced the oil filter while I was in the area. The old one was a Fram and I figured, whats $6. The oil was changed about 2K miles ago and is running 10W30 weight. Considering changing it again, but holding off as I think of that as grasping at straws.

As to the rocker cover, I'm holding off on that until I can verify the pressure at the engine. I looked into the filler cap area and everything immediately around there seems to be oiling just fine, but am considering doing this in a few days. Right now, this is a spare vechile for us and just letting it set will not be an inconvience in the short term.

Basically, my biggest issue is trying to find the cause of why the pressure guage is acting differently over the period of a week. I could certainly live with 40-50 lbs of pressure if everything else is ok.

what oil filter did you install to replace the old fram. Like i said, with a freer flowing oil filter (like the ford fl 300) you will get an increase in oil pressure (and that is a good thing. LOW oil pressure is the bad thing because it leads to a lack of lubrication and metal on metal damage.. the 4.0 actually has really low oil pressure at idle compared to a l0t of other motors). If you changed to a different brand or model oil filter ... that is your key to your change in oil pressure. Btw, you should search "oil filter" and you will see a lot of debate about which oil filters are good and which ones suck. WIX filters which are sold at napa as their nambe brand tend to have a really good reputation. This is a pretty neat article that may interest you. http://minimopar.knizefamily.net/oilfilterstudy.html

FYI. since you have a 2000 I'd like to draw your attention to something else you should be aware of. The 2000-01 models came with distributorless ignition systems and to meet higher emission standards the revised the head of the motor and the heads model # is 0331. These heads sometimes crack and allow coolant to enter your engine compartment leading to motor failure. Keep an eye on your coolant and if you have a mysterious loss of coolant over days/weeks of driving, you may have a problem. I feel its better to inform and be prepared in advance than to have you learn about it after serious engine damage may occur. search "0331 head" and you will find a LOT of info. I don't want to scare you, tons of people have high mileage on their xj's and their heads are fine, but it is something to acknowledge. heres a start http://www.naxja.org/forum/showthread.php?t=92545&highlight=0331

I used a WIX filter this time around. But I do want to point out that this sudden change in pressure didn't coinside with an oil change. I changed the filter after, sudden jump in pressure. I HATE when things are suddenly different and I can't find a reason for it.