Help Diagnosing Engine Knock


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The Goblin

The Goblin

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Has there been any progress on this? Mine has the exact same noise and curious if its a cracked header or not...
Has there been any progress on this? Mine has the exact same noise and curious if its a cracked header or not...
Sadly not yet. Still working on narrowing it down.

The way the sound seems to be affected by the temperature of the engine, or the length of time the engine has been running, leads me to a few things:

Exhaust leak - specifically cracked exhaust manifold. The crack could become more evident as the metal heats up. But I can't see any tell-tale marks where exhaust could be leaking.
Lifter issue - Sound starts about 15-30 seconds after the engine starts up, so it could be related to the time it takes for the oil to get pumped up to the lifters/rocker arms, etc.
Piston slap - The shape of the piston/skirt could change as the metal heats up. I don't think it's this one because I visually inspected the pistons multiple times from underneath and I could not see any play at all, but that was when the engine was cold so I may be wrong.

And then there is still the pesky flex plate. It still could be a crack in the flex plate because the sound seems to come from the bell housing/back of the engine area.

So, sorry to say, I have not yet discovered the issue.

Keep us posted if you figure out what yours is. I will surely do the same.
 

dom.robles

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Orange county
Sadly not yet. Still working on narrowing it down.

The way the sound seems to be affected by the temperature of the engine, or the length of time the engine has been running, leads me to a few things:

Exhaust leak - specifically cracked exhaust manifold. The crack could become more evident as the metal heats up. But I can't see any tell-tale marks where exhaust could be leaking.
Lifter issue - Sound starts about 15-30 seconds after the engine starts up, so it could be related to the time it takes for the oil to get pumped up to the lifters/rocker arms, etc.
Piston slap - The shape of the piston/skirt could change as the metal heats up. I don't think it's this one because I visually inspected the pistons multiple times from underneath and I could not see any play at all, but that was when the engine was cold so I may be wrong.

And then there is still the pesky flex plate. It still could be a crack in the flex plate because the sound seems to come from the bell housing/back of the engine area.

So, sorry to say, I have not yet discovered the issue.

Keep us posted if you figure out what yours is. I will surely do the same.
i know its been a few weeks now im wondering if you have broken any ground on youre knock. I'm currently trying to diagnose that exact noise in my 2.5 from the same area of the engine as well
 
OP
The Goblin

The Goblin

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Syracuse, UT
i know its been a few weeks now im wondering if you have broken any ground on youre knock. I'm currently trying to diagnose that exact noise in my 2.5 from the same area of the engine as well
Sorry, nothing yet. I haven't been able to do much on it for a while, too busy at work lately. I will post updates here. If you find anything out about yours, please post it here too so the rest of us can learn! Good luck with it!
 

nsiciliano2

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Nov 28, 2020
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Raleigh NC
Sorry, nothing yet. I haven't been able to do much on it for a while, too busy at work lately. I will post updates here. If you find anything out about yours, please post it here too so the rest of us can learn! Good luck with it!
I just finished reading this entire thread what an awesome thread thanks for diving head first into this problem that so many people have. I have the EXACT same noise coming from my TJ that you have. This whole thread has been extremely informative. Please keep us posted. I’ll be following closely.
 
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The Goblin

The Goblin

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I just finished reading this entire thread what an awesome thread thanks for diving head first into this problem that so many people have. I have the EXACT same noise coming from my TJ that you have. This whole thread has been extremely informative. Please keep us posted. I’ll be following closely.
Thanks for coming along on the journey! Sorry to hear you are having the same problem. It seems to be more common than I expected. Would be nice if there was one clear fix for it, huh?

If you find anything out with yours, please post here so we all can benefit. Thanks!
 
OP
The Goblin

The Goblin

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I just finished reading this entire thread what an awesome thread thanks for diving head first into this problem that so many people have. I have the EXACT same noise coming from my TJ that you have. This whole thread has been extremely informative. Please keep us posted. I’ll be following closely.
Thanks for coming along on the journey! Sorry to hear you are having the same problem. It seems to be more common than I expected. Would be nice if there was one clear fix for it, huh?

If you find anything out with yours, please post here so we all can benefit. Thanks!
 

nsiciliano2

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Nov 28, 2020
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Raleigh NC
Thanks for coming along on the journey! Sorry to hear you are having the same problem. It seems to be more common than I expected. Would be nice if there was one clear fix for it, huh?

If you find anything out with yours, please post here so we all can benefit. Thanks!
You’re telling me that sound is enough to drive you nuts! I’m getting ready to drop my oil pan and check out my timing chain. I’m sure it’s all relatively fine but it’s process of elimination at this point haha..
 
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The Goblin

The Goblin

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You’re telling me that sound is enough to drive you nuts! I’m getting ready to drop my oil pan and check out my timing chain. I’m sure it’s all relatively fine but it’s process of elimination at this point haha..
Lol! Right??

If you do end up dropping the pan, let us know how it goes. I didn't find anything out of the ordinary when I was under mine. I ended up changing the chain as well because it looked pretty stretched out, but it didn't get rid of the noise, sadly.

What engine do you have in your TJ? Is it the 4.0? If so, and you do end up changing the timing chain, the pulley removal tool from Harbor Freight was a God-send. It has a shorter main bolt in the set so you can remove the crank pulley without having to remove the radiator!

The ones for rent at O'Reilly or Autozone all had longer bolts for their pulley removers so they wouldn't work for me unless I removed the radiator, which I really did NOT want to do.

Good luck!
 

nsiciliano2

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Lol! Right??

If you do end up dropping the pan, let us know how it goes. I didn't find anything out of the ordinary when I was under mine. I ended up changing the chain as well because it looked pretty stretched out, but it didn't get rid of the noise, sadly.

What engine do you have in your TJ? Is it the 4.0? If so, and you do end up changing the timing chain, the pulley removal tool from Harbor Freight was a God-send. It has a shorter main bolt in the set so you can remove the crank pulley without having to remove the radiator!

The ones for rent at O'Reilly or Autozone all had longer bolts for their pulley removers so they wouldn't work for me unless I removed the radiator, which I really did NOT want to do.

Good luck!
Yea I’ve got the 4.0 in mine as well. I’ll definitely look into that tool thanks for the heads up. Im interested to see if I find anything when I drop the pan... I’ll keep you posted.
 

nsiciliano2

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Yea I’ve got the 4.0 in mine as well. I’ll definitely look into that tool thanks for the heads up. Im interested to see if I find anything when I drop the pan... I’ll keep you posted.
So I’ve been doing some research about lifters and before I go tearing into my oil pan I wanted to check to see if any of you had any experience or info in regards to replacing/freeing up lifters. As of now I’m leaning towards my sound being a lifter issue versus something coming from the bottom of the engine.

Thanks!
 

bromel

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So I’ve been doing some research about lifters and before I go tearing into my oil pan I wanted to check to see if any of you had any experience or info in regards to replacing/freeing up lifters. As of now I’m leaning towards my sound being a lifter issue versus something coming from the bottom of the engine.

Thanks!
The sound we're hearing in this thread is almost certainly the lifters. It's an extremely common noise with the 4.0s. You can try Marvel Mystery Oil to try and wash some of the gunk out of there, but to truly eliminate the noise, you'll have to replace the lifters, and that means you'll probably have to replace the camshaft since they wear together.

But, honestly, why bother? The 4.0 is a noisy engine. My Cherokee with 255k sounded like that from more or less day 1, and it currently has 256k with no issues.
 

nsiciliano2

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The sound we're hearing in this thread is almost certainly the lifters. It's an extremely common noise with the 4.0s. You can try Marvel Mystery Oil to try and wash some of the gunk out of there, but to truly eliminate the noise, you'll have to replace the lifters, and that means you'll probably have to replace the camshaft since they wear together.

But, honestly, why bother? The 4.0 is a noisy engine. My Cherokee with 255k sounded like that from more or less day 1, and it currently has 256k with no issues.
I gotcha, I was kinda leaning towards just letting it go since it’s a little bit of a project to replace it all. I’ll look into the mystery oil for sure. I know the zinc additive was mentioned a couple times in this thread. Thoughts on that?
 

bromel

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I gotcha, I was kinda leaning towards just letting it go since it’s a little bit of a project to replace it all. I’ll look into the mystery oil for sure. I know the zinc additive was mentioned a couple times in this thread. Thoughts on that?
Yeah, talking about zinc on this forum is like arguing religion or politics. I'm of the opinion that you don't need to add zinc because modern oils provide the necessary lubrication for flat tappets, and what little benefit you might see is outweighed by the damage the zinc will do to your cats. Ultimately there are so many 200,000-mile 4.0s out there owned by people who barely changed the oil on time let alone added zinc, and can anyone here actually point to a lifter/camshaft failure on a 4.0? I've never heard of one.

Obviously they've happened before, but it would take an epidemic of failures to prove that these engines need zinc additives.
 

nsiciliano2

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Yeah, talking about zinc on this forum is like arguing religion or politics. I'm of the opinion that you don't need to add zinc because modern oils provide the necessary lubrication for flat tappets, and what little benefit you might see is outweighed by the damage the zinc will do to your cats. Ultimately there are so many 200,000-mile 4.0s out there owned by people who barely changed the oil on time let alone added zinc, and can anyone here actually point to a lifter/camshaft failure on a 4.0? I've never heard of one.

Obviously they've happened before, but it would take an epidemic of failures to prove that these engines need zinc additives.
Haha right on I appreciate it. That makes sense. I’m a little crunched for time right now. But I’ll give that mystery oil a run and see how that goes. Thanks again
 
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SkylinesSuck

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Ultimately there are so many 200,000-mile 4.0s out there owned by people who barely changed the oil on time let alone added zinc, and can anyone here actually point to a lifter/camshaft failure on a 4.0? I've never heard of one.

Obviously they've happened before, but it would take an epidemic of failures to prove that these engines need zinc additives.
I have had several. One was bone stock so it pertains. The other ones were with high lift cams with stiff springs so not apples to apples. I have heard several guys on the stroker forum that have killed cams the same way as well but again, high lift and stiff valve springs. I don't go out of my way to say stock 4.0's need it.
 

Harcust

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Hey, all! I was brought here from The Goblin's YouTube videos. He recommended I join because I commented on YouTube that I have a 2001 4.0 I just purchased making nearly the same exact noise.

When I cold start the jeep it's quiet for a few seconds but as the oil pressure builds the noise starts and peaks after about a minute. The noise slowly starts to fade away as the engine warms up to nearly nothing at operating temperature. Based on The Goblin's excellent work troubleshooting the bottom end I figured I'd start at the top end.

I did read somebody's suggestion in this thread to let the Jeep get warm, shut it off and let it sit for a few minutes before starting back up. Sure enough, I shut it down for about three minutes and started it back up and the noise was back only this time I could hear the lifter pump back up rapidly in a few seconds. It's making me really want to chase a lifter issue now.

I plan on uploading some videos as well and trying to contribute to this thread as much as others have.

Thanks!

20210104_164959.jpg
 
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reddvltj

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Hey, all! I was brought here from The Goblin's YouTube videos. He recommended I join because I commented on YouTube that I have a 2001 4.0 I just purchased making nearly the same exact noise.

When I cold start the jeep it's quiet for a few seconds but as the oil pressure builds the noise starts and peaks after about a minute. The noise slowly starts to fade away as the engine warms up to nearly nothing at operating temperature. Based on The Goblin's excellent work troubleshooting the bottom end I figured I'd start at the top end.

I did read somebody's suggestion in this thread to let the Jeep get warm, shut it off and let it sit for a few minutes before starting back up. Sure enough, I shut it down for about three minutes and started it back up and the noise was back only this time I could hear the lifter pump back up rapidly in a few seconds. It's making me really want to chase a lifter issue now.

I plan on uploading some videos as well and trying to contribute to this thread as much as others have.

Thanks!

View attachment 215611
Have you tried doing an engine flush yet? You could also try adding a small amount of Marvel Mystery oil to the crank case then run it for about half an hour then change the oil?
 

Harcust

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Have you tried doing an engine flush yet? You could also try adding a small amount of Marvel Mystery oil to the crank case then run it for about half an hour then change the oil?

I've only had the Jeep for two weeks and haven't really had a lot of time to mess with it and troubleshoot. I did change the oil two days ago and I replaced one quart with Marvel Mystery Oil. The bottle says replace up to 20% which is about what I did. I've only started it a hand full of times in the driveway and haven't really been able to run it good since the oil change. I'm getting it inspected this Wednesday and will be able to drive it more then (pending inspection results).

I remember reading about a trick on the 5.3 LS engine a while back about spraying carb cleaner or a similar solvent directly down the pushrod and let the lifters soak in it. If the Marvel Mystery Oil doesn't clear it up, I'll try that next and if that doesn't work I'll pull the valve cover and investigate more.

I also had already ordered a timing chain but after seeing The Goblin's results I'm probably going to replace it latter down the road and try some top end stuff first.
 

bromel

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Looking forward to your journey. Would be nice to confirm once and for all that this common noise is from the top end and not something more serious.

More specifically, I wonder if there is anything that can be done without removing the head, e.g. replacing rocker arms. Since the noise seems to be coming from deep in the engine, I've always assumed it's the lifters, but sounds can certainly radiate.

What's prevented me from considering replacing the lifters is that they wear along with the cam shaft, which I've heard could cause problems unless you do everything at once. That and nearly every 4.0 makes the same racket, so clearly it isn't causing major damage.
 

Harcust

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Looking forward to your journey. Would be nice to confirm once and for all that this common noise is from the top end and not something more serious.

More specifically, I wonder if there is anything that can be done without removing the head, e.g. replacing rocker arms. Since the noise seems to be coming from deep in the engine, I've always assumed it's the lifters, but sounds can certainly radiate.

What's prevented me from considering replacing the lifters is that they wear along with the cam shaft, which I've heard could cause problems unless you do everything at once. That and nearly every 4.0 makes the same racket, so clearly it isn't causing major damage.
I'm glad you're looking forward to it, I'm not 🤣. Joking aside, I didn't want to buy this Jeep and immediately have to do major engine work. I didn't hear the noise during the test ride.

For now, here's a few video I made previously. The first two were recorded the same day I changed the oil. The last video was a cold start the next morning.

This is shortly after a cold start:


This is from that same start but with the engine at operating temperature. Ignore that I focused on the EVAP solenoid for a second:


This is the next morning, first start of the day. If you notice the noise doesn't start immediately but as the engine oil pressure starts to rise: