I tried just the filter, and no difference. Although it does hold pressure just a LITTLE more often, but the idiot light still comes on and it reads 0psi every now and then.

I didn't have time for the oil pressure gauge, but I'm going to do that tomorrow.

Let's assume the gauge is correct.

I know the rod bearings and main bearings are in good condition. Cam bearings? Cracked head? I've read a lot about the 0331 head in these 2000-2001 cherokees.

I'm just curious because I'm thinking about switching it to another head even if it's not cracked, but since I have the coil pack is there any reason I can't use an older year head like a 98? There is one on craigslist right now for $75

 

You'd have to make up coil pack mounts. No big deal. If the head was cracked your oil would look like a milkshake. Check the pressure first....

 

^^^x2 How well does your engine run? Any noises?

 

Cam bearings are a big possibility. Year 2000 had some issues with cam bearings walking out of its bore. Do you see any small metal flakes in the oil? Cam bearings have the GREATEST effect on oil pressure. Believe it or not the 4.0 can survive with a worn/missing cam bearing! Mine reads almost zero and triggers the alarm every time I come to a stop but it has done that for years. Worn lifter bores will have a major effect on pressure too. I have heard of people who have bought re manufactured 2000 engines with low oil pressure from the get-go. The important thing is...do you have oil pressure at highway speed and does your engine run ok. If so, drive it.

 

The engine runs great, the oil was good when I changed it, and it has a tick. I'm pretty sure it's a lifter and I even have on to replace it, I just don't want to take the head off, so if I do I will probably wait until I get another head just in case mine is cracked.

It's got good power the only thing wrong is the tick (which I know is VERY common) and the oil pressure.

Can a blown lifter cause low pressure?

 

No, just one bad lifter shouldn't cause low pressure...BUT a worn lifter bore OR multiple lifters can. Also if the rocker fulcrum pivots are worn enough to allow play (valve lash) this will allow oil to leak out of pushrod rather than being forced through the tiny orifice on the rocker arm.
If THAT is the cause of your low pressure there is no reason to be alarmed. Your engine is still getting lubed. The reason pressure returns when rpm is increased is b/c the pump output is exceeding the leakage rate.

 

I had the same problem with my 2001 (had the cracked head.) But I saw you checked the bearings and oil already....

 

slim chance im sure but any chance this is your noise (hope i dont offfend your intelligence)



sure it isnt the famous flexplate scraping tick? caused by either loose flexplate bolts or a cracked flexplate. click here if you


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