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Help with diagnosing rattling noise under light load

gearwhine

NAXJA Forum User
Location
Denver, CO
I'll try to be as complete as possible. I feel it's all required to provide some input

I bought a 1996 Jeep Cherokee I-6 AW4 NP231 with ~135,000 a few months back.

Starting off....everything runs great, no stuttering, no rumbling, no shifting issues. It's all tight and doesn't feel under-powered. No OBDII codes are present.

I changed the oil to NAPA Synthetic 10w-30 with a NAPA/Wix Platinum Filter. I changed the air filter with it.

A week or two later, I noticed a slight rattling sound. I'm not necessarily saying it started at that point...I'm just saying I noticed it. It happens under extremely light load and up when moving or not moving. I can re-created it with my e-brake on and a press on the accelerator. It's pretty much unrecognizable at idle. It does become prevalent (to me) when I lightly place my foot on the accelerator....so light that the RPMs don't even go up. I feel that detail might be important...maybe?

I first checked all the basics...fluid levels etc. Recognized I forgot to connect my air intake back in the throttle body, so I essentially ran ~200 miles bypassing the air filter. Whoops...likely a non-issue from my diagnosing at this point.

I then looked at the shop information from the previous owner, and it was always maintained with 5w-30 Amsoil synthetic for the 5 years of back data I received.

I have now driven it around 5-600 miles since that time. The sound has not appeared to get worse. It's hard to hear if I have HVAC on medium to high....but my ears are tuned so perfectly to hear the rattling now.

My current diagnosing-

I have gotten nearly everywhere with a stethoscope (stethoscope diagnosing is new to me, so I don't know what sounds are normal). It does sound like the bottom end has a more metallic sound at idle. Not ticking, not thumping...just sounds like the crank bearings are dry or something similar. I take it that's a normal sound...but throwing that out there. I'm likely going to change back to 5w-30 this weekend to see if that sound changes.

Valve cover sounds great even when applying gas with my hand at the throttle body lever. Head sounds smooth.

I have have tried 85, 87, and 91 octane fuels...no change....so very likely not pinging.

I am not seeing any issues with exhaust....but that doesn't mean it's not a leak or a metal contact I'm missing.

I have placed the transmission into neutral with no accelerator during cruise speed. The rattle is still there, but it's not as loud.

I have used sound deadening tape at many interior plastic contact points...my interior is pretty damn noiseless.

Any other thoughts on potential causes? I'm beginning to think it's a non-issue.

Thanks!

-Nick
 
sure it's not exhaust? maybe drop by an exhaust/muffler shop just to be sure. they can look for any metal on metal contact points you may have missed? had this issue with rattle at the gas tank skid plate that I couldn't see from the ground with my untrained eye.
 
...........
A week or two later, I noticed a slight rattling sound. I'm not necessarily saying it started at that point...I'm just saying I noticed it. It happens under extremely light load and up when moving or not moving. I can re-created it with my e-brake on and a press on the accelerator. It's pretty much unrecognizable at idle. It does become prevalent (to me) when I lightly place my foot on the accelerator....so light that the RPMs don't even go up. I feel that detail might be important...maybe?.............

My 96 has the same rattle. After checking the torque converter bolts, I've just about isolated it to the catalytic converter. It's louder on the passenger side and can be heard when laying on the ground next to the cat.

There was a recall on the cats for the 96 model year. It seems the honeycomb material was breaking loose from the case and rattling around on the inside...
 
My 96 has the same rattle. After checking the torque converter bolts, I've just about isolated it to the catalytic converter. It's louder on the passenger side and can be heard when laying on the ground next to the cat.

There was a recall on the cats for the 96 model year. It seems the honeycomb material was breaking loose from the case and rattling around on the inside...

can confirm this is also true, and when mine finally bit the dust it failed smog. I was worried there was some other issue causing the cat to fail like there usually is but fuel trims are good and as soon as the cat was replaced it passed ca smog easily.

I'm betting it's exhaust related
 
Thanks everyone.

To answer MickeyS's original question....definitely not sure about anything!

With that...I'll scour the entire exhaust system thoroughly before anything else. I'll bring it to a shop if I find nothing. It did pass Denver air emissions and inspection when I bought it though...so it's likely not entirely toast even if the sound is from the cat.

I do recall now that my previous 96 had a cat issue. When I pulled it off, it basically had a clump rolling around in it. That happened with only around 50k miles on it.

If I find nothing, I'll go back to 5W-30 and see if anything changes with lifters or bottom end noises.

I'll then check purge solenoid. Appreciate the input so far!

-Nick
 
Another possible source would the timing chain. There is a factory dampener inside the timing cover. It was originally a piece of rubber. By now it is hard as plastic. Perhaps under the right conditions something is going on between that dampener, the chain and the cover.

IIRC that dampener is on the passenger side of the timing cover, meaning it is behind the AC/Alternator brackets where they mount to the cover. IOW, it will be a PITA to try to get to that area with a stethoscope/wooden rod.
 
You can just disconnect the purge valve solenoid for a few minutes and drive around. If you don't hear the rattle you know the solenoid is the cause.
 
I finally got around to replacing my catalytic converter, because of the rattle.
Once removed, it's obvious where the noise is coming from. The honeycomb
material had broken loose from the housing and was rattling back and forth
inside the converter shell.

Because of the U-clamp Jeep used to connect the cat to the intermediate pipe,
it's necessary to cut a slit in the pipe in order to slide it over the bulge created
by the U-clamp. I used a cut-off wheel but it still took a long time cutting through
the stainless steel of the cat pipe...
 
Hey all,

Just following up since a new post has come in...and it seems Runnin' has fixed their problem, which is great!

No repair or diagnosis yet on mine. I did just recognize a slight head gasket leak (visible off the front), so that's going to be what I attack next. I'll be able to check the timing chain then. I'll absolutely post as things come to fruition.
 
Got under my hood is do some engine work, and finally found the crack in the manifold. Now that I see it, I see this is exactly where the common cracks are on these things:doh:. Not sure how I missed it before, but some extra space always helps.

Can't say it's the cause of the rattling I've heard, but it's absolutely a problem. I'll report back when it's all fixed up.

enhance
 
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