Alright. I have been searching all over the forums here and I think I have an idea what my next step it.

I just picked up a 93 xj 4.0 with almost 200k miles. And the oil pressure showed 0 and was told the pressure sender was bad, checked the plug and it had oil on it like it has been leaking internally. I figured if it did have low to no oil pressure the engine would make some God awful noise but it sounds like normal valve train noise and I drove it home about 40 miles away no problems no extra noises.

I did hook up a manual guage and low and behold the pressure wouldn't climb.

I can almost hear a knock I think but it's so faint compared to the rocker/valve train noise.

I got bored and did a high volume oil pump and new 10w30 with a quart of Lucas oil stabilizer and the pressure went up like 5 psi.

By the looks of things the next best bet would be to do main bearings and rod bearings? I should have checked them while I did the pump but I didn't have access to a small enough torque wrench to put it back together.

Thanks again.

 

Before you go any further take the oil pressure sending unit out. Then run a pipe cleaner in the hole and down through the elbow.

Assuming you didnt already do that then you might be extra lucky and just have a simple blockage to the sensor.

You could also jam a piece of hose over the fitting, run it into a bucket, and start the engine to see if there is any flow at all

 

I used some wire to "clean" the oil pressure sender port and it felt clear, and the engine seems clean (no sludge or any build up of anything in the pan) but anyways... Alright had time to do the rod bearings, attached is the ones that I pulled out. Starting from the left is cylinder 1 lower then upper ect. I did plastigauge them prior and never got a reading over .002ish so I wasn't convinced it was the problem but still replaced em.

Well according to the pressure sender nothing changed. Got rid of a knock tho so I'm getting somewhere. Going to head to a machine shop next week to find some main bearings or should I pull the whole filter housing and clean it out?

Ps it's running a FRAM filter I know I should try a different one.

Pss. It doesn't sound like it has low oil press, my buddies 2.5 is Hella noisier with over 40 psi... will hook up mech guage tomorrow to re verify psi.

Psss thank you.

 

Well found the problem and I'm a dummy. Apparently these run really good on 5 cylinders. I should've been smarter and used my head as my oil pressure was not building at all, not falling off when warm kind of no oil pressure and taken the small missfire as a clue. Anyways my intake push rod is a lot shorter than the other on cylinder 1. And it pushed the lifter out of the hole and that's where all the oil pressure is going. I think.

Tell me I'm on the right track haha

 

I’m far from an expert but I have read many times on this and other forums that the cam and it’s associated parts are what have the greatest affect on oil pressure.

 

Agreed! But it was a mix of main bearings and rod bearings and cam bearings from what I read and re searched about oil pressure. But all of them were once the engine got warm the oil pressure would drop.

Mine just wouldn't build pressure at all regardless of temp or engine oil type. I just didn't put 2 and 2 together and should have looked sooner. Gotta keep it simple.