Oil Pump Failure

My '94 Cherokee's oil pressure gauge is almost bottomed out while running. At 160K I think that's pretty unheard of. I threw in a new pressure sending unit ($40) which didn't change a thing. I've heard that a clogged oil filter can do the same thing. Is this a fact?

Before being aware of how noisy the 4.0 is, I complained to the dealer where I bought the vehicle about the noise when it was new. As a result they threw in a high volume oil pump at no cost. Perhaps this is a quotient to the early failure?

Doing a search didn't bring up anything so I'm assuming this is a pretty rare issue with the 4.0. It sounds like a pretty straight forward job:
1. Jack up the car on stands so the axle droops
2. Remove the starter
3. Remove the oil pan
4. Remove the pump
5. Replace the pump
6. Replace the oil pan and starter
7. Crank the engine with the coil wire removed to check pressure
8. Start the engine and check for leaks.

Is this it? I've also read where the exhaust downpipe needs to be removed. Are there tricks to getting a good seal on the oil pan gasket? Not a bad time to replace the rear main seal either.

I'd appreciate everyone's thoughts and thanks in advance.

Are you sure your pump failed? The 4.0 pump is a very simple unit, 2 gears a check valve/spring and the housing.Hook a mechanical oil pressure gauge up where the sending unit is and see what you are getting. You can pick up a cheap gauge at Oriellys for $20

IMO more likely to be a few things that add up rather than an oil pump failure. Connecting rod bearings are the easiest to check and change if necessary, raised my oil pressure to acceptable.
I've also taken the cover gasket off the oil pump and resealed the bottom cover with a little silicon. The oil pump often wears more on the face rather than the gears. Tightening up the lateral clearance of the gears by removing the gasket helped some. Just make sure to turn the oil pump over with a screw driver from the top to check if it doesn't get too tight if you remove the oil pump cover gasket.
A seriously clogged up oil pump screen can also starve the pump. My pressure relief valve (inside the pump) was seriously gunked up and hardly moved at all.
Like I said, IMO it is likely to be many things that add up instead of just the pump, though anything can fail

XJtrailrider: Thank you. The only reason I haven't bought a pressure gauge is that is it seems there are only 3 failure options: The sending unit went bad which I replaced, the pump, or a clogged oil filter. The gauge is working because its not showing no pressure: just very little and the needle just wobbles near zero.

8 Mud: Thank you. That still means removing the oil pan which gets back to my original post: Minor surgery. Also please know that this happened rather suddenly (I think). The car sits for long periods of time. I've been teaching my 16 year old how to drive a stick. OMG!!! Since he was behind the wheel I'm not sure exactly when in happened but the symptoms were not gradual.

What brand of oil filter are you using?

Don't know about the filter. Its whatever junk the quicklube throws in there.

By the term NOISY do you mean the usual piston slap that most earlier XJs were known to have or are we talking about the impending destruction of the engine?
The bottomed out oil pressure could also be caused by a plugged oil pressure port. If the engine is gunked up as was previously posted then the port for the oil pressure sending unit could be obstructed too.
Several years ago a local Jeep owner posted about no oil pressure and even after replacing the sending unit; there was no pressure observed on the gauge. Using a dental pick I found that the port was plugged with gunk and after clearing the port and bumping over the engine; oil squirted out. Once I installed the sending unit oil pressure was read on the gauge.

CharlesS said:

By the term NOISY do you mean the usual piston slap that most earlier XJs were known to have or are we talking about the impending destruction of the engine?
The bottomed out oil pressure could also be caused by a plugged oil pressure port. If the engine is gunked up as was previously posted then the port for the oil pressure sending unit could be obstructed too.
Several years ago a local Jeep owner posted about no oil pressure and even after replacing the sending unit; there was no pressure observed on the gauge. Using a dental pick I found that the port was plugged with gunk and after clearing the port and bumping over the engine; oil squirted out. Once I installed the sending unit oil pressure was read on the gauge.

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Thanks for the good info Charles: I was referring to the normal piston slap. I'm the original owner of this vehicle and the oil has been routinely changed every 3500 miles with few exceptions so I can't imagine that its gunked up but its always a possibility. Never say never, right? I think I'm going to buy a gauge and get a reading, toothpick in hand.

Before you button it back up check the oil ;ick up to pan clearance.

I just finished replacing my oil pump. I had no psi at idle. 200000 on the odometer so I thought worn bearings. removed pan and found one of the pump bolts was out letting oil bypass right back into the pan. plastigauged my bearings and they are within spec. new pump has 20 psi at idle vs. less than 5 with the old. You never know what you will find so tear it down and check it out.

lofin0704 said:

I just finished replacing my oil pump. I had no psi at idle. 200000 on the odometer so I thought worn bearings. removed pan and found one of the pump bolts was out letting oil bypass right back into the pan. plastigauged my bearings and they are within spec. new pump has 20 psi at idle vs. less than 5 with the old. You never know what you will find so tear it down and check it out.

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Thankyou. I plan to do so.