Engine Noise—Jeep Thing or Major Issue?


RFC

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I've got a new noise in my '99 4.0 and I could use some expertise in helping diagnose it. The oddest part is that it only makes this rattle on flat ground or if the nose of the jeep is pointed upwards. Does not make the noise going down a hill or if the backend is slightly higher than the front.
  • Engaging the clutch has no effect, so seems like it's not the transmission or transfer case.
  • I removed the serpentine belt and ran briefly thinking it might be the water pump, no change.
  • It makes the noise regardless of engine temperature, but recently has gotten more pronounced on cold start for a few seconds.
Is this thing about to grenade?

Ignore the lifter/piston slap knock which does go away once the engine warms up.

 

BryantJT

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I don't know what that is but it certainly isn't good. I'd be pulling off the oil pan and maybe looking into the timing cover as well.
 
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RFC

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I can't tell if the noise is there when driving with all the road noise/wind etc., but it's always there when idling, IF i'm level or with the front end up. It goes away if I'm pointed downwards.

Will need to a get stethoscope, but without one it is much more pronounced from underneath or inside the cab.
 

Chris

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I don't know what that is but it certainly isn't good. I'd be pulling off the oil pan and maybe looking into the timing cover as well.

X2, it sounds like something is completely broken off and rattling around in there.
 

Rubicon88

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If you don't have a stethoscope you can use a makeshift one...

Long screwdriver with handle against your ear opening. A long hose in the same fashion too will work.

The more I listen to it I swear I hear a tinish kind of noise. Without pin pointing exactly where....but from the tone of it I swear I can hear throw out bearing noises in that video.

Good luck and let us know
 
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RFC

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If you don't have a stethoscope you can use a makeshift one...

Long screwdriver with handle against your ear opening. A long hose in the same fashion too will work.

The more I listen to it I swear I hear a tinish kind of noise. Without pin pointing exactly where....but from the tone of it I swear I can hear throw out bearing noises in that video.

Good luck and let us know
The previous owner obviously did not care for it at all and I've been working through a whole host of problems, so I don't doubt that your ear might catch other issues.;) It seems like as soon as I fix one thing, then I can actually hear the next problem.

The noise is an odd one and it is kinda tinny and rotational in nature. I'll hear it rattle to a stop when I shut the engine off from inside. At first I thought it was the t-case chain but that seems out as it makes the sound when in neutral or with the clutch depressed, then I thought maybe water pump impeller scraping the housing. Nope.

Was (unrealistically) hoping for it being some known and relatively easy fix...

It's great to be back in the Jeep world (very first car was an '87 Cherokee two door) and very much appreciate all the knowledge and help on this forum!
 
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dom.robles

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I've got a new noise in my '99 4.0 and I could use some expertise in helping diagnose it. The oddest part is that it only makes this rattle on flat ground or if the nose of the jeep is pointed upwards. Does not make the noise going down a hill or if the backend is slightly higher than the front.
  • Engaging the clutch has no effect, so seems like it's not the transmission or transfer case.
  • I removed the serpentine belt and ran briefly thinking it might be the water pump, no change.
  • It makes the noise regardless of engine temperature, but recently has gotten more pronounced on cold start for a few seconds.
Is this thing about to grenade?

Ignore the lifter/piston slap knock which does go away once the engine warms up.

im nowhere near an expert i'm currently trying to diagnose a knock in my 2.5. but judging by your sound i think you may have a broken pushrod and it is getting bounced around in there. might be worth pulling the valve cover and taking a look in there, the valve train is a common source of engine noise in these engines anyway
 

Fughuert

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From the sound and your description of how it comes to a stop when you shut the engine off I’m thinking timing chain tensioner.

Mine sounded very similar. Basically the sound is your chain is bouncing around on your cover, if I’m right.

Lasted 4 days after the noise was at its worst. Easy fix on the 2.5, more disassembly required for the 4.0 not too bad though.
 
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RFC

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Would that change depending on if the Jeep is pointed uphill or down? I picked up a mechanics stethoscope and it actually sounds more like it’s coming from the bellhousing
 

Fughuert

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Would that change depending on if the Jeep is pointed uphill or down? I picked up a mechanics stethoscope and it actually sounds more like it’s coming from the bellhousing
I can’t say yes or no to that but if it is the timing chain these are non interference engines so just make sure you have aaa.

Did you try to listen to the timing chain cover?
 
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RFC

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I can’t say yes or no to that but if it is the timing chain these are non interference engines so just make sure you have aaa.

Did you try to listen to the timing chain cover?
I havent yet, but certainly will do before I start taking things apart.
 
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RFC

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Could also be catalytic converter bricks rattling around. Does the 99 have the cats up on the driver's side of the engine?
Not on mine, it’s still the older single cat system. It’s weird that the sound will disappear completely if I’m driving downhill. Perhaps that does point to the timing chain if it’s loose enough to rub against the block when driving up hill but spinning freely in its cover when pointed downwards.