89 XJ no oil pressure

Alright, well I got the jeep started, and noticed there was no oil pressure. The other night while I was taking things apart I noticed a good ammount of carbon build-up under the valve cover, tore it apart real quick and gave it a quick cleaning. Today I got it to the point of turning over, turned strong and tons of black smoke came out, it actually stained the driveway! Now tomorrow I'm going to be pulling the oil pan, theres no leak on the rear main seal, but i want to cover the bases on this. What should I look for when I pull the pan? I threw some marvel in the oil the other day when I changed it out & put a new oil filter on it today. I'm thinking after I change the pan I'm going to throw a quart of atf in there, it worked for me on other engines in the past. I don't hear any knocking or ticking from the enging, there is a clank but it seems to be from the mechanical fan. Any advice is welcome, Ive only driving it about 200 yards and let it Idle for about 15 minutes to help break up the carbon. Anything else I should do?

Well cranked it up before i went to the park with my wife n boy and had steady pressure, so im guessing its just gunk building up on the pick up, we'll see when i pull it tomorrow.

Before pulling it apart I would use a mechanical oil pressure gauge to confirm what pressure I had.

If/when you pull the pan don't forget to re-torque the main and rod cap bolts/nuts, they work loose.

Depending on your pressure readings from the mechanical oil pressure gauge and the mileage on the engine you might consider replacing the oil pump. I recommend using a HIGH-VOLUME oil pump in the 4.0--the gears are cut better than in the OEM stock pump and the HV pump at NAPA is just a few bucks more than OEM.

If this were my vehicle, I'd like to understand the root cause for this.

1. As Joe mentions, use a mechanical oil pressure gauge for this (can be rented from many big box parts stores).

2. What is the history of routine oil changes on this engine? That is a common cause for "sludge" in an engine. If that is the case, frequent oil changes can help alleviate this.

Below is the specs for oil pressure on the Jeep 4.0

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

i just bought this jeep for $500 a week ago, the sludge isnt as bad as I would have thought for a 200K+ vehicle, but it is a high mileage vehicle. I did test it with a mechanical pressure guage, while it was running & expelling the carbon it didn't register; no pressure, but later when I tried again it was fine around 15 psi at idle. Thanks for the input, I might replace the pump, ill have to think about it. I'm trying to keep it as low-buck as humanly possible, I'll def. go through and re-tourqe everything possible though, thanks!

I think if you are going to go thru the trouble of dropping the pan. I would get some plastic gauge from napa and check the rod and main clearance. I think your oil pressure @ 200k is evidence there might be a little extra clearance there. Just my .02 cents. I just put rods and mains in a 2005 gmc with a 5.3 and picked up 20 psi hot at idle. Good luck

cashsxj said:

I think if you are going to go thru the trouble of dropping the pan. I would get some plastic gauge from napa and check the rod and main clearance. I think your oil pressure @ 200k is evidence there might be a little extra clearance there. Just my .02 cents. I just put rods and mains in a 2005 gmc with a 5.3 and picked up 20 psi hot at idle. Good luck

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deffinently will look into it, just another hour my wife will be pissed at me!