Hi all,
Been a lurker here and have had a account for awhile. I have read a lot of great info here in helping on my little build. Anyways, long story short. I have a 89 cherokee 2 door Sport 4.0 w/160,000 miles, its all stock, I bought it for $500 and runs great now after 1k in parts and my labor over the past year.

I was out wheeling a bit and got lost in a area and barely made out before dark(no gps). I was getting on it some because i was in a hurry to get out of this area. I made it home ok and never noticed anything weird at all with the way it ran. The jeep sat for 5 days and i went to start it today and its knocking horribly on the top end area and running very rough. The oil pressure gauge does not respond at all. Whats bugging me is I cant even remember what is normal readings on that oil pressure gauge...duh

So should the first thing I do is get a oil pressure gauge and test at the sending unit? and what pressure should i see and how do I perform this test after I hook up pressure gauge?? Do you start and run vehicle for a bit or? I was going to get a harbor freight one tomorrow($27). This is really bugging me as I have done a lot of things to get this thing purring, now this...lol

Thank you all so much in advance!
Troy

 

There's oil in the pan? You didn't mention whether or not you checked the level.
If yes, then check the pressure. Screw the gauge in place of the electrical sender on the oil filter adapter housing. 13# at idle is what the factory considered minimum, some run fine with less.

 

Thank you very much for the reply. Yes it was only a half qt. low when I checked yesterday after i started it and it was knocking hard. Oil looked good on the dipstick. Will get a tester and report back.
Thank again!

 

Yep, use a manual test gauge. Replace oil pump if it is really at zero. Spec for the 4.0 is 13psi or so at hot idle, so you'll see something above that typically when you cold start it. If it is really reading zero, turn it off immediately, and replace that pump.

 

Is the oil pressure sending unit plugged in?

Just change the oil recently?

If so, what brand of oil filter did you use?

 

Replacing the oil pump is unlikely to do anything. It is more likely there is a dead bearing somewhere. Actually a few. It will require a full rebuild to fix.

 

All the wires hooked up and spark plugs in place?

 

I bet that squirrel has a cholesterol problem