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Knock in 4.0...with video and sound

your motor sounds like a diesel. Id check for a cracked exhaust manifold. It could also be lifter tick which is extremely common on the 4.0s.
 
Sounds like normal 4.0 lifter noise to me. You get use to it after 8 years and 60,000 miles in an 87 jeep with 275,000 miles on it.:D
 
How long has it been that way? Did it start abruptly or slowly over time?

It is really hard to tell but it is starting to sound like rod knock to me.
 
Talyn said:
Sounds like piston slap. Too slow to be valve train noise.
Click to expand...

"Too Slow"
I disagree. Why would a single noisy lifter (valve train noise), be any faster that a single piston "slap"?

It sounds just like my 87 use to sound, and I have done no mechanical repairs (oiled area) to the engine in 6 years, or 50,000 miles. Mine would show up on cold morning ups, loudest then. Get 90% quieter as the engine warmed up.

Ever since I started exersizing the engine at 3800 rpm once in a while, it has gone to sounding like a quite sewing machine at worst, 98% quieter than it worst cold morning first start up. Initially cleaning the old oil with snake oil additives, like MMO, and adding Lucas to the 10W40 I originally used helped a lot. But the real thing that worked later was getting the RPM up 3700 for 60 seconds once the engine was warmed up, once in while in winter months. Mine almost never makes that noise now. Before I learned the 3700 rpm trick, you could hear it a block away on real cold (45 F or lower) morning start ups. Now it rarely makes any noise even on a cold start.

Thus concluded it was sticking and or noisy lifters. I do not believe rod knock would come and go like that, nor piston slap?
 
It started getting noticeable about 2 weeks ago...and is mostly at idle. I run Rotella 10w-30...and have tried all the snake oil additives...but the oil is CLEAN...like REALLY clean.

How key is 3700 rpms? I ran it at 3000 for 3 minutes the other day to no avail.
 
jimmy21669 said:
It started getting noticeable about 2 weeks ago...and is mostly at idle. I run Rotella 10w-30...and have tried all the snake oil additives...but the oil is CLEAN...like REALLY clean.

How key is 3700 rpms? I ran it at 3000 for 3 minutes the other day to no avail.
Click to expand...

I was told that there is something key about 3700 rpm in the 4.0 that gets the lifters rotating again, after they get stuck and stop rotating. All I know is it works, and 3700 rpm seems to be the minimum rpm sweet spot to unstick the lifters. I know several people that tried it and liked the results.

Mine was stuck running in DD stop and go traffic for years and never got over 1400 rpm due a bad TPS, which is partly why it got that way.

If it does not solve your problem, then it maybe something else as suggested by others here, or the lifters may be too far gone. But mine sounded like a sledge hammer beating on the block at its worst, like serious rod knock. That has not returned in over 10,000 miles and 2 years now.
 
That sounds like my Jeep when the flex plate cracked. Either you have to pull the tranny or have a flexible video scope to see.

009.jpg

006-1.jpg
 
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