i have an 89 mj with 4.0 auto 215,000 miles. has a loud knock espicially when first cranked up after sitting. just hard to tell where the gremlin noise is coming from. knocks under accelration up till about 35mph then goes away unless it downshifts. tried the seafoam in oil trick, runs a little smoother now, took off valve covers rockers and pushrods where fine, seemed to be squirting oil like a champ. with valve cover off noise doesn't seem to be coming from top end. after running for a while when stopped the oil pressure dummy light starts glowing. does this sound like a rod/main bearing, oil pump, flexplate/flywheel crack? any help would be appreciated

 

so after reading a lot of threads, it sounds like a flexplate issue to me, but that doesnt explain the oil pressure light

 

4.0 engines are known for engine noises.... valve train noises,wrist pin chatter, piston slap ,broken piston skirts ,lower end noises(excess bearing clearance),loose flex plate bolts, cracked flex plate ( i've seen pictures of this ,not pretty). just drive it till it blows up! 96 cherokee 4.0 249.000 miles doesnt burn any oil ,leaks a little. engine knocks a little until fully warmed up(15 mile drive) daily driver,plus ive heard other high mileage 4.0 s make the same noises.

 

Mine sounds wonderful!
Its always nice hearing your engine knock echo off buildings in the morning.
It quiets down when warmed up, but is never gone. We think its a cam/lifter.

 

i figured ill check the torque converter bolts anf flex plate for cracks. if i dont find anything, oh well. go or blow. 4.0's are cheap to replace, or there is always the small block swap

 

no knock is normal by any means. You probably had low oil pressure, personally i would never even own a car without a proper oil pressure gauge i mean...thats just asking for trouble. I had low oil pressure issues with my XJ and i now run Mobil1 oil filters with cheap wallmart synthetic oil and did more frequent oil changes for 10,000 miles. Works FINE. The I6 in our cars especially non HO ones (a lot less cases of rod knock in non HO motors) will run forever if properly maintained.

Hook up a mechanical gauge to anyone that has any kind of "knock" pull the sender out of the block and screw in a mechanical gauge i will guarentee that knock has been caused by low oil pressure.

My wish to you is its carbon deposit buildup causing the knock.

 

so if it is bad oil pressure, yall think its just a pump/bearing problem? not used to working on these engines, give me a subaru wrx or toyota supra engine and im good, but the 4.0 is new to me.

 

Mine sounds like a diesel when I start it up...haha. Burns a lil oil too, then as it warms up gets quiet and stops burning oil. I jus let it warm up for a good 10 min or so before I drive usually...no biggie

 

After running 3 full quarts of lucas oil treatment in the past 2 months honestly all my knocking and little engine noises have stopped. the main thing you can hear is the exhaust that has a leak and my fans going

 

maybe it will just hurry up and break then at least ill know where the noise was coming from exactly.