hi guys,

i have an 89 Cherokee Laredo with the 4.0L and Auto trans with 314k miles. This month the engine started to make a "rapping" noise, sort of like someone is tapping it with a hammer or something. My cousin is a mechanic, and he looked at it with the valve cover off (changed the oil and added mystery oil while we were at it) and he cant say for sure if its a lifter or rod or what. he said rod knock is usually deeper than this sound, and while hes a very good mechanic, he doesnt want to tear the engine apart since its probably easier to just swap it. The oil pressure is low at idle and as the engine gets warmer and the load increases (like going uphill), the oil psi just drops off (gauge on the dash reads 0, and it has stalled in the past, havent driven it much since). He put a "real" oil psi gauge on the engine while it was idling and while it was on the low side, it didnt spell imminent death. it seems to idle fine and apart from the noise, its hitting all 6 cylinders and has plenty of poke.

So my question is two-fold. A) is this a common occurance with these engines when death is imminent? 314k is a lot of miles.
B) if its time for a new engine, what years, etc. should i be looking for? I found a 99 4.0L HO on craigslist, but somethign tells me a 99 engine isnt going to work in an '89 truck. also, how much should i spend? my cousin and i can do the work ourselves so labor cost is not an issue. also, i dont "need" this truck, its just kind of a spare vehicle, but if i can keep it running for a few hundred bucks then i definitely will.

 

Take a long screw driver, have the engine running. CAREFUL! of any moving pulleys! Place the driver around various areas of the engine, one end of the valve cover, other end on your ear[use the handle for your ear]. now listen....front or back end of engine, up top or lower down, try various places. the driver with work like a steth-i-scope [wrong spelling] It will transmit noises to your ear. this can tell you if it's a lower noise or upper.

What was the gauge reading for the oil pressure? The real gauge...let us know.

314000miles is plenty high, so a re-build might not work, check around with engine shops, get a quote. Worse case quote that's what you want, call for used engines as well, use a guy that's been around for awhile.

Hope this helps.

 

yeah i know about the stethoscope, but honestly it doesnt matter if its a top or bottom end noise, it spells replacement either way since my cousin will swap the engine, but doesnt want to take the current one apart and i cant blame him, lol. definitely dont want to bother with a re-build, id be looking for a used engine- i just need to know which years will work- i know the 90s and newer engines are different, but i dont know if that means that they wont still swap in.

i want to say the gauge was reading around 20 at idle.

 

there is a section on engine swaps here in the forum, tells which years and how to's.

Just can't remember where i read it....do a search, there's a lotta good info on this site.

20psi is a good number, but.....if things are rapping.

could be a stuck lifter??? With the cover off, see if any rocker arms are loose...

 

technical write ups/ how to's

try there...i think..

 

nah the rocker arms were all tight... after using the mystery oil, the noise seemed more toward the low end... i think its probably a rod. i looked for the info in the tech section, it looks like 87-90 are the same engine, (Renix?) but i dont know if the chrysler-injected engines are also compatible.

 

not sure on the Chrysler injected....good luck, keep us informed as to your direction with this.

 

well i drove it around yesterday in an attempt to get it to die again for lack of a better term and while the rapping noise is still there and the oil psi gauge on the dash is reading 0, the damn thing is still running, LOL! i thought for sure it would shut down with a 0 reading from the oil pressure, but apparently not. other than the noise and lack of apparent oil pressure, it seems to be running fine.

 

Sounds like what my jeep is doing, I have a video if you want to see it. You can tell me if it sounds like yours.
We just bought the jeep, Im gonna drive it till it blows.
has 205,000 on it..

That video is how I got my sig...
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you prob have excessive bearing clearance..which is the main cause for low oil pressure in HIGH milage engine...315K is alot. id try to pull a 96-98HO motor (NON-CFC) with around 100K (easy to find) and swap it over.

 

yes, thats exactly the sound! i think my oil sender might be bad though, because today i gave it a quick workout and the oil psi stayed around 20-40 and it drove exactly like it did yesterday when the gauge was at 0. someone commented on your video that it was a "piston shroud"? idk, it sounds kinda logical but im not familiar enough with these engines to say for sure.

i guess im just going to run it till it starts sputtering and dying again (just hope im close to home; dont want to get stuck paying for a tow) then look for a motor. my mech thought it was a spun bearing at first, but the valves looked fine, and oil is getting to them so its kinda like... wtf?

i shuold mention that this happened all of a sudden... i was tooling down the highway with the mrs on our way to move a mattress and it squealed, popped, had no power and was knocking like crazy... made it home knocking and dying up any kind of hill, parked it for 3 weeks or so till my mechanic could look at it... its been running fine ever since though. full power and just the crazy noise.

 

welp, im pretty sure its a stuck lifter at this point. it really doesnt sound like a rod, and aside from the noise, the truck is running normally. the oil psi gauge reads normally again too, so im just going to drive it and not wander too far from home, LOL.