I really would have no idea how to describe this sound so I took a short video in hopes that someone will hear and be able to help diagnose the sound.

All I can say is it's a light rattle sound, kinda like a knocking but it's not really consistent like a knock would be. Kinda sounds like bad piston slap?

Anyway, it's a 1996 XJ with 193,000ish miles. I have owned it a year and since ran Rotella 15w40 with Napa filters. I put a new oil pump in when I did the oil pan gasket and rear main in January. The noise has always been there just slightly, but over the past few weeks it has gotten much louder.

 

Bump

 

What does it do when you rev it?

 

Pretty much goes away. And it is much less noticeable when the engine is warmed up.

 

Dude one thing I've noticed is these motors love to chatter...i read a bunch of posts that said to run the engine for 15 minutes at 3500 rpm to free up sticky lifters which were chattering very badly...dont you know it actually worked!...172000 miles and the 4.0 sounds like a new engine...give it a shot man

 

Do this before anything else.

https://www.cherokeeforum.com/f51/ho...ocking-125547/

 

If its coming from underneath I would check the flexplate like mentioned.

But my knock came from the engine bay..it would go away when I revved it too... I ended up blowing a hole in my block when I floored it one day. So baby that thing until you find out what it is.

 

My thoughts:

Check the flexplate bolts and re-do them anyway with LocTite. It's a known problem and it might just be the OP's only problem. Chalk it up to maintenance.

 

Well I pulled the inspection cover and looked at the flexplate. All looked good. Went ahead and pulled the converter bolts and applied loctite as instructed, torqued them back down and.... no change to the sound of concern:-( It was worth a try at least, really hope it's not going to throw a rod through the block here soon.

Any other idea?

 

My 94 sounded like cummins injector rattle at idle.Tryed engine restore snake oil with great results.Got 210k on it now,use every oil change.

 

Just don't floor it like I did.

 

Check this out. Worthy of a sticky IMHO.

https://www.cherokeeforum.com/f2/fou...emoval-171945/

 

Hmmm I have the same noise. Had it when I bought the jeep never thought much if it but now will definitely will get under there to check the flex plate

 

Straightshooterjeeps cracked flexplate diagnosis

I removed 3 of the 4 bolts.

Then loosened the last bolt about half way.... I left this one in to maintain connection between the tq and the plate. Just so I wouln't have to fiddle with putting bolts back in too much.

Now the flexplate is pretty much seperate from the torque converter.

Got my flashlight pointed up in there

Grabbed a big flathead screwdriver and started prying on the flexplate

Don't see anything yet

Turn the flexplate a half rotation

Pry again

and there it is! A big fat crack up near the center of the plate.

When the flexplate is loose from the torque converter you can get it to "flex" real good and you just might be able to spot your crack.

Just to be sure you do have one before dissasembly.

It was very obvious at this point, but before pulling those bolts I looked and looked and could never see a crack.

Hope this helps save someone a little time.

 

mine sounded like that and it was my harmonic balancer hitting the timing chain cover...
Cameron