First post and I'm looking for some tips on troubleshooting my 01 XJ. I've owned it since new. It was my wife's daily driver, completely stock and without any major issues, current mileage at 175K. My wife retired it last month meaning its my toy once again

During a few recent trips I discovered that it makes a load whirling sound when 4 hi or lo is engaged. The sound doesn't start until after the Jeep reaches approx 10 mph+ and stops as soon as I let the gas off. No noise in 2wd and 4wd seems to work (minus the noise). I've read a variety of posts with similar symptoms and see everything from CV boots to blown transfer cases.

Another issue that recently developed is the oil pressure drops to zero during idle and rebounds as soon as I accelerate.

Any tips on what I should check 1st for either issue?

 

Any ideas? Just looking for the order of things I should check to diagnose the issue. Haven't wrenched on anything driver train related so I have little experience to fall back on.

And to add to the 4wd symptoms... It seems the sound started a year or so go according to my wife (who tells me this now). She said that she would hear the whirling/grinding sound when 4wd was first engaged; however, it would decrease in intensity and eventually end following by a thud...

 

How loud of a whirl is it?

The oil pressure dropping to zero doesn't sound good. You should get that verified with a mechanical gauge. The pressure sending units do go bad.

 

Oil pressure and transfer case are completely unrelated.

Start by checking you have the correct amount of fluid in your transfer case, your engine, and your front differential. Try it then. Next step would be to check related components such as u joints and other rotating parts. Someone else will have to chime in on the oil issue, I'm less experienced in those regards.

 

Agree with Jerry for the 1st issue. Check your fluid levels, (it is probably a good idea to replace it anyways), my XJ whined very loud in 4wd until I replaced the axle u-joints.(one had a bunch of play (minimal needles left in the cap), the other was quite seized). Certainly check the u-joints to make sure there is no play, and they otherwise look alright. In 4WD, you can certainly tell its there, in regards to noise, and especially at higher speeds. If it seems excessive, or significantly more than before, it's probably worth checking out.

 

Linkage might need adjustment. x2, 3, whatever on fluids and joints.