So went to work today half way there and all of a sudden a knocking nosie was coming from the engine bay. On my way back from work the knocking was still there the moment I started the jeep to when I drove back home but now it has gotten very quiet at idle and only gets louder when pressing down on the gas. From what I check it could be piston slap or the torque converter bolts coming undone but from what I read they usually stay at constant nosie level or get louder not quieter? (Unless I'm wrong which then please correct)

 

The way to answer this is to pull the inspection plate on the front of the bell housing and check the bolts for tightness. All the other ways with a stethoscope etc will not answer the question definitively.

 

Go on u-tube and type in your noise and ask for sounds of piston slap or what ever. Been there for my older chev 350. Also how to diagnose the sounds . Alot easier than waiting for a reply from a forum when you can find out right away.

 

Sounds caused by metal worn away don't typically start suddenly so I would lean away from rod knock and piston slap and look at loose or cracked flex plate. The other good thing is that those are pretty easy to inspect and fix compared to piston slap or rod knock.

 

https://www.cherokeeforum.com/f51/ch...xplate-172081/

 

A simple way to test for cracked flex plate is to tap it with a wrench or something and if it tings is not cracked , if thuds then is is cracked . Tranny shop told this method and worked for me even thou I took the flexplate off to see if maybe he was wrong. Wasted a bunch of time but I had to know

 

Bolts are about 100 times more likely to be loose than the plate cracked.

 

Just a tip for cracked flexplate

 

So sorry it took so long for update, but we found are culprit which is lifters. So I started to order parts but in the mean time I changed the oil to what is recommended from factory and the filter ( the filter is an STP and yes i know that is not a good filter but its the only one I had at the time I will change it to a better one when I change the oil again). I will run it for about a 1,000 miles then chage it again and see if the new oil will make the noise go away. I know its a long shot but hey it could work.

 

Substitute 1 quart of Marvel Mystery Oil for regular oil and run it hard. Might just fix it.

 

Ok will give it a try.

 

<highjack>
Would you give that same advise for a Subaru that has developed a lifter tick after it has fully warmed up and has 310,000 miles? I would put in the spare engine and rebuild, but I'd rather not have to for a little longer so I have time to rebuild the 4.0 in the Jeep.

See how I tied that back to relevant?

</highjack>

 

Try some seafoam. I've used it. It works. I also trust this guy on Project Farm:

 

Yes, I would use it on a subaru.