I have a 96 jeep cherokee sport 4.0L 4x4 with 190k miles. The last couple weeks I noticed a hard knocking when I do a cold start. When i am driving I can hardly notice it, mainly if i hit a bump it may clunk a bit. If I have the jeep in drive but stopped, the knocking is slight but still there. As soon as I shift it into park and the jeep vibrates more, the knocking is noticeable a lot more.

So in short, I hear the knocking loudest on a cold start, and once the jeep is warmed up and in park. Mainly when the vehicle is shaking/vibrating the most.

Any ideas?

Thanks

if it is an auto, i would suggest checking your flexplate for cracks......

yeah it is an auto, I am going to assume the flex plate is hard to get to lol. Is there any harm in driving with a potential crack in it? Other than the noise, I have no issues starting, driving, and it seems to shift when it should.

Is there a way to tell if it is the flex plate without tearing into it?

A cracked flex plate usually makes noise upon acceleration no matter the temperature.

I can notice the sound slightly during normal driving at a slow speed just because the jeep is not as loud, but what ever it is making the sound, it sounds like it is a spinning part. The sound has no pattern to it, and when i turn the jeep off, it gives a few loud, slowing farewell knocks.

The sound does not intensify while accelerating and is not audible while just driving down the road.

broken exhaust mount causing exhaust pipe hitting somethin?

there is a very good possibility of that. My manifold has a crack like no other, and a few mounts in the back have rusted loose, I didnt think to look in the middle though. I will give that a good look tomorrow while it is running. I was waiting on the damn pos to break before dealing with it, maybe it is a sign of stress coming from somewhere down the line due to a broken mount.

Maybe it is time to bite the bullet on the exhaust manifold and the rest. Check the catalytic converter for loose internals.

Could you have the mechanical cooling fan hitting the fan shroud due to a broken or misplaced shroud or worn engine mount?

I finally got time to get under it today and just look around, the exhaust looked fine, it was not hitting anything. The knocking sound was brutal when I was looking, sounds like a big chunk of steel smashing into something, but it was muffled like it was inside something. I hope that makes sense, I am not very knowledgeable on terms.

I still find no pattern to the clunks, it seems like every couple seconds there will be a louder knock followed by a few smaller ones, stops for a second, does it again, but there is no consistency in the noise.

try to get together with some guys who are local to you and have someone with a little more experience check it with you. if its not rythmic then its something loose because any rotating assembly would be. do you have bad motor mounts or something like that and its letting the engine vibrate more then normal and maybe hit the mount arms or something?

I read another thread where an engine knock was traced to loose bolts between the torque converter to flex plate. They're relatively easy to check.

that happened on my wife's 95 a number of years back. if its not rythmic then it won't be that though because that sounds like a bearing knock. i know when i heard it i sure thought it was that. i had to call my dad and have him listen and he said its either main bearings or the bolts on the torque converter. i put new bearings in real quickly and then did hte bolts and it turned out if was the bolts. oh well, jeep had new mains after that.

Here is a bit more info for you all before I finally get time to look at it sunday with my dad (who knows well more than i do about jeeps lol).

I noticed after it warmed up and i rolled my windows down at a stop, that there was much more rhythm to it, yet much less sound/very fast tapping/rattling. The knocking seemed to get a bit better recently. It started quieter today at work, drove 15 mins home and shut it off. 5 mins later I started it up to run to the store, and it really hesitated and knocked worse than ever, and finally started. So much so that I was scared to shut it off at the store in case it didnt start again lol.

After that incident, drove the mile or so back home, sat in park for almost a minute and noticed no knocking...I can not figure this out, I will get back to you guys Sunday night when I hope to know what in the hell that sound is.

sorry to be long winded, waiting for one of these poor explanations will bring a new idea to the table. I will check for the bolts Sunday as well

I would listen real close to the cat convertor they ball up inside and rattle to beat the band.