cypher

Hey all
Got some questions about my oil pump. I've got a '96 ZJ with 157,000 miles on it. As of a few weeks ago I noticed that the oil pressure gauge started to dip more than I would think is ok. Usually, while driving even stopped at a light, the gauge usually sits in the middle of the gauge, on the number 40, right in the middle of the gauge. Now, whenever I come to a stop, the gauge has been dipping down to right about the 20 hash mark, maybe just a bit above it. The oil level is fine, however it does need to be changed. The first thing that came to mind was the oil pump is either clogged somehow or it's on it's way out, or maybe the oil filter is clogging...? I don't think I even put 3000 miles on it since I changed the oil last.
So I figured I'd just replace the oil pump. Then I read the process involved just to get to the damn pump. You've got to be kidding me...detach the exhaust pipe at the catalytic converter, remove flywheel inspection cover, remove the starter motor, jack up the vibration damper to relieve tension, remove the motor mount through-bolts then jack up the whole motor to get enough clearance to pull the oil pan out the rear..?! Seriously? What a pita that's gonna be! I don't think I can afford to bring it anywhere and I only have 2 floor jacks with no jack stands yet.
Anybody ever have to change the oil pump on their ZJ? Is this really the only method of doing so? Or, is my pump even the problem? Any insight into this would be much appreciated.
Thanks.

mjonesjr

Once a 4.0 is warm, it will idle with around 20 PSI oil pressure. Under normal driving conditions, the oil PSI will be around 40.

I don't think you have a problem. If there is any problem, it seems to be a bad pressure sensor.

BTW, changing the oil pump isn't as hard as it sounds. It takes about 3 hours total to swap them out.

HCCAFan

Man that sucks. It's a lot easier on a XJ I guess.

mjonesjr

Changing the oil pump on a ZJ or an XJ is the same procedure.

HCCAFan

I've done my oil pump and I didn't do half of what he is talking about.

JeepingDan

https://www.cherokeeforum.com/f51/ho...e-works-82130/

You may wanna watch this.

mjonesjr

Then you must have a lift.

If you don't have a suspension lift of roughly 4", you will have to jack the motor up to get the oil pan to clear the front suspension. Changing the oil pan can't be done without removing the oil pan, which can't be done without removing the starter and transmission inspection cover.

That video is somewhat correct.

All pumps create pressure or the fluid wouldn't be moving. What creates the higher pressure is the clearances in the engine.

Just saying an oil pump doesn't create pressure is not true.

xj2

for me it was easiest to just pull the axle. once thats done i didnt have to pull my starter or inspection cover. it was a little rough getting the pan to break the seal because of the old gasket material. but came out. be sure if you dont have the new one. to pull, spray(carb clean) the oil pump pickup tube and screen clean. the reason for pulling the axle helped me most when it came time to prep to put the oil pan back on. removing the old material was a pain. but can be done effiecitvely with pnematic die grinder or highspeed sander with scotch brite discs.

but as for the low oil pressure problems your having. be sure to hook up a mechanical guage first.

HCCAFan

I have 2" pucks in the front. That's it. THe pan came right out with some wiggling.

Bustedback

They don't create pressure, resistance to flow creates pressure. Oil pumps are rated in gallons per minute, or volume, not in PSI. Low oil pressure is caused by worn out engine bearings, not because the oil pump is not making pressure.