Fluctuating oil pressure and rough idle

98 cherokee with 4.0 and auto tranny. 194k on the od.

I have a little bit of a rough idle intermittently. The jeep runs perfect otherwise.

I have noticed that when the jeep is cold the oil pressure is erratic. It usually starts up around 40 and will occasionally bounce around until its warm where it will idle around 15psi. The gauge never bottoms out or drops below about 15. Like I said other than that the jeep runs perfectly. Oil pressure around 35-40 psi cruising at 40 - 50 mph when warm.

I have also noticed some of the other gauges will bounce around a bit from time to time as well. Including the temp and volt. Fuel gauge is rock steady.

I am thinking that there may be a grounding issue and intend to go through the grounds on saturday. I have no ticking, banging or othewise nasty noises from the engine bay.

Could faulty ground/grounds cause this issue? I have also read that worn rod and main bearings can cause this issue and the way the pressure is fluctuating matches the symptoms of worn bearings. I would think that there would be some kind of noise associated with bearings that would be worn enough to cause this.

Ideas from anyone who has seen, heard or read about such an issue?

edit to add: Oil last changed by jeep about 1500 miles ago. Mopar filter and Pennsoil 10w-30.

Thanks!

Pennzoil is one of your problems..
You can pull your cluster and clean the contacts.
I would recommend purchasing/renting a mechanical oil gauge and verify your pressure. Maybe rent/buy/borrow a obd scanner to check/verify your other temps/readings.

Im going to change it to Rotella in a little bit.

I had a free oil change from jeep lol

stockli said:

I have also noticed some of the other gauges will bounce around a bit from time to time as well. Including the temp and volt. Fuel gauge is rock steady.

I am thinking that there may be a grounding issue and intend to go through the grounds on saturday.

Click to expand...

The fact that the other gauge readings bounce around is a clue. I would suspect a possible connection issue with the dash cluster. Remove it, clean the electrical plugs thoroughly with electrical contact cleaner, add a dab of dielectric grease and reconnect. Verify grounds for both the cluster AND the engine bay. Grounds are the cause of many electrical gremlins.

Another thing to consider is that your oil pressure sending unit is heading south. They are a very common failure. I recommend purchasing them directly from Jeep for the best reliability/accuracy/mating with your factory gauge. Well worth the extra money.

I don't think the brand of oil is involved in your symptoms, and as long as your oil pressure readings are in spec, (factory spec listed below) you are okay.

*Not less than 13 psi at HOT idle
*Between 37-75 psi over 1600 rpms