96 cherokee 4.0 engine noise/knock
 

96 cherokee country 4.0 ho 4 W/D auto trans, 246.000 miles .i have a noise from my engine that sounds like a rod knock. the noise is most noticeable when engine is cold. it seems to diminish when the engine has warmed up a little, but is always there. just about every jeep 4.0 i have heard running has this noise , so i did not worry about it to much. recently i changed the oil (10w/40) castor oil high mileage 4.69 aquart...ouch $$$$. now my engine noise/knock seems louder? i have heard about 4.0 having a issues with piston slap ....could this be the noise? i have also heard of the torque converter bolts coming loose causing quite a lot of noise. any help or experience with this problem would greatly be appreciated!:icon_confused::sad:

Is the noise constant through all rpm ranges or does it get quieter as you accelerate?

typically if it is a rod knocking it will get louder as the engine warms up. check the converter bolts to rule that out.

cherokee 4.0 engine noise
 

the noise disappears as you rev it mainly because of the fan and engine noise. when you hold it at say 1500 rpm you get kind of a rattle noise like wrist pins rattling? i dont hear the noise when driving , just at idle or under the hood.:icon_smile:

at 1500 in park or neutral you are at no load. any "rattle" or "knock" could be main bearings or flywheel/converter. when driving, the drive line is under load and will tend to quiet the noise.

If the noise stays constant then it could be torque convertor bolts making contact with the bell housing. If it gets quieter as the rpms come up and louder when they return to idle, it could also be a cracked flexplate.

noise is not constant ,just around idle speed. cant hear it while accelerating. :icon_cheesygrin:

i think what we're saying is rule out the easy fixes. the torque converter bolts or a cracked or broken flywheel. i wouldn't jumped right to a rod or main bearing causing the noise. look at the exhaust system as well. i have heard of missing hangers causing noise by the pipe hitting the underbody that could be mistaken for engine noise.

Let's put it this way. My 91 started with a very slight tick that grew into a symphony of hammers in the bottom end. Two different shops refused to even look at it because they said the could tell the motor was trash. Did a little inspection and found tiny cracks in the flex plate and was given a quote of $900 to replace it. I got another flexplate from the jy, spent $130 on a transmission jack (very wise investment), and invested about 8 hours of profanity in the driveway to change it out.


This is what the old one looked like.
Attachment 11696

thanks for the advice and the picture! that flex plate is complete toast ,i have never seen one do that before. i will definetly check my flex plate and bolts....as soon as it stops raining. :sad: another thing ,as i mentioned i had changed my oil recently. the noise got louder after the oil change on start up after getting done? it had 10w/30 in it and i put in 10w/40 high milage type expensive oil ....could this change cause a engine to knock ? thank you for your responses ...much appreciated!:thumbup: