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Dieseling type noise/lower end noise

A

Abner

NAXJA Forum User
Location
colorado
I have a new to me 92 with a 4.0 and AW4. When it gets up to operating temp the lower ends seems to be making some noise that almost sounds like a diesel. Any ideas of the problem and the cure? I was going to put a new rear main in soon, so i wonder if i should do some bearings while i'm in there? If you need any additional info please let me know. The jeep has 192k on it and I was told the motor was rebuilt a few years ago.
 
Funny enough.... I'm from colorado.. and also having the same issue and questions.. I've got the main seal in a box in the trunk..

It runs strong and smooth and only burns a puff of oil when I really MASH on it..

Mine is a 91 with the 4.0 and an AW4 142K and no rebuilt motor... 2nd owner.

Maybe it's the altitude? (a joke you'll only get if you're a texas import)
 
If you drive a stick and you try to accel from too high of a gear and the engine rpm is too low you will get a noise that sounds exactly like a diesel engine. I know exactly the sound you are talking about.

You can probably relate this to your automatic somehow by saying it's probably not downshifting into the correct gear for you to accelerate at the rate which you want to.

you should probably check out your tach and see what the engine is doing whenever it makes that noise.

My .02
 
I know exactly what you are talking about and that is not it. The noise is most noticable at a stop, or idle. Once you get some road noise it drowns it out.
 
I bought my 97 about a month ago for a good price. Thought there was a rod bearing going out. Loud at idle but quieter at higher rpm's. Turned out to be flexplate/torque converter bolts were loose. Really easy to check and after I did a bunch of searching old posts turns out it's really common.
Mine is a 4.0 with the AW4.
 
Abner said:
I have a new to me 92 with a 4.0 and AW4. When it gets up to operating temp the lower ends seems to be making some noise that almost sounds like a diesel. Any ideas of the problem and the cure? I was going to put a new rear main in soon, so i wonder if i should do some bearings while i'm in there? If you need any additional info please let me know. The jeep has 192k on it and I was told the motor was rebuilt a few years ago.
Click to expand...

Its hard to say without hearing it but it sounds like the infamous 4.0l piston slap if its only doing it at idle. It could be a few other things though.
 
Both the 4.0s Ive had do this, It seems common and not detrimental if you will. sounds like clatter from the oil pan, my 95 has 185K does it hard and I recently ran the u know what out of it hitting the revlimiter several times and it still hasent came apart or otherwise, uses no oil to speak of etc. Years ago I had toyota 4x4 that did the same thing. After researching it I found on some years the wrist pin was slightly off centered and caused "knock" at low speeds and idle.
 
Abner said:
I know exactly what you are talking about and that is not it. The noise is most noticable at a stop, or idle. Once you get some road noise it drowns it out.
Click to expand...

Ditto... most noticable in the drivethrough while at idle or low speeds (under 2mph)
 
That's funny my parents have a 97 Plymoth voyager that makes the same sound..... I hope it's not the flex plate... isn't that between the transmission and the motor (the automaitc trans equivalent to a flywheel?)

I think it may be the piston slap thing now that you said that I'm thinking ti sounds alot like our voyager and it's made that noise for 80K and it works fine runs smooth and doesn't use oil... not detrimental just concerning to a new owner I suppose..

Glad it isn't something bad!
 
I have this same sound at 221k. I did the rear main recently, plastigaged all the bearings. Nothing loose. Changed the rod bearings for good measure (only $5 each, old ones didn't look great.) Put it back together, no difference (except less leaking :).) Tried 3 or 4 different weights of oil, no difference. Checked the Torque converter bolts, seemed tight enough, but I'm going to check again. For now I just drive it :)
 
probably the flexplate, but I remember reading about someone else having problems with a rattly noise which ended up being the oil pump. The screen at the bottom of the pick-up was a little loose and rattled sometimes.
 
I've got the same problem too. I'm gonne drive mine up on some ramps in the morning and check it out. How hard is it to check the tq converter bolts? I was told there is a cover to remove...anyone got a picture?
 
Sounds like a rattle at idle. Like something metal is hitting something. At first I thought it was a BAD rod knock, but it doesnt do it when you give it gas or anything more than idle.
 
You guys are not alone. My '91 has 190k and has done it since the day I've had it. In addition to that, my friend has four of these things, -and all of them do it as well.

From a mechanical standpoint, they sound like a real POS, -about to come apart, -but they just keep running, -and running pretty well.

Mine does seem to be doing it a little louder after I found a pond that was a little deep last weekend (not good, don't ask!)

Worst case scenario (in my case) is a collapsed piston skirt or a bent rod. My pushrods are all straight, so it's likely something else.

I've decided to button it back up and drive it, -because the noise all but disappears once the engine comes up to temp. I'm going to continue to run it and see what happens. I'll bet it stays together and runs just fine, -if not, so be it, lesson learned..........
 
My 95, 131k, has the same knock sound at idle but goes away around 5 MPH. I just bought this a few weeks ago for my daughter and to me it sounded like a rod bearing. I took the old filter and cut it open and checked the filiment for metal and found nothing. I'm thinking its the wrist pin making the noise. I will however be checking the flex plate during my next trip under the vehicle. I just spent the better part of 3 weeks fixing it up and putting a lift on it so it will be a few weeks before I get under it again. I'm getting to old for this Shi@.
 
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