Hi, I am having an issue with my 2008 JKUR (with the 3.8l).

Occasionally I hear a strange marble noise after decelerating. It is hard to make it happen when I want it too, but I was able to record it … twice. To my ear, it sounds like it is coming from the valve cover area, near the passenger side firewall. It has been happening for quite a while now, till now when I decided to dig more into it. Actually, my wife was driving it today and mentioned that it kind of shuddered when she was at a stop sign. So, I am looking into it now, haha.

(be sure to enable closed captions as I added commentary)

Here are the facts that I am aware of:

• 3.8l jeep with less than 150k miles
• new plugs and wires last fall
• no obvious vacuum leaks (will run more tests this weekend)
• no CEL codes
• Superchips 87 tune
• new brake booster check valve and seal last summer
• oil change 1000 miles ago (mobile 1 synthetic high mileage 5w30 with an extended wix xp filter)
• oil changed religiously at 5000mi. (easy to keep track of)
• The marble noise tends to show it self more when the oil is getting to the lower 1/3 of the dipstick.
• I usually have to add a quart every 3000 miles, although, recently, on the last oil change, i filled it up, and 2 weeks later it was 1/8 of an inch below the low mark and the marble noise was quite noticeable. But the engine did not sound any different otherwise. We dont drive it much now since working from home, and haven't put nearly 500 miles on it. I put a little over a quart in it to top it off and it hasn't gone down at all in the past month. No oil puddles in the garage either.
• dry start sound if the jeep has sat for more than 24 hrs. (shouldn't happen with the wix xp?)
• I installed the glowforge oil filter pancake adapter so I can install a pressure gauge during the last oil change. Haven't ordered the gauge/sensor yet.
• New oil pan gasket 6000 miles ago. Kit came with a new o-ring for the pickup tube but I did not see a screen on the end of it.
• runs great 95% of the time. I can hear a light chatter when accelerating up a hill though. Might be the same noise as the marble sound, but cant tell for sure with all the other road noises.
• while idling in the garage, I can detect the slightest hiccup in how it runs if I place my hand on the jeep. It is hardly noticeable and cant hear it.
• driver's side exhaust manifold was replaced in 2019
• after the spark plug wires were changed, we towed our camper to VA and melted the 2 rear spark plug boots on the drivers side (new manifold) from indirect heat. replaced the wires in VA and burned those up on our return trip. Replaced the wires again and bought fiberglass socks to put over the boots. I read that it could be an issue with aftermarket headers. Hasn't been a problem since. But might have strained the coil pack?
• 4.88 gears, 32" tires, auto, kept the rpms between 2500rpm - 3500rpm while towing (depending on terrain)

I am thinking the hesitation could be a vacuum leak, dirty throttle body, or a sensor going bad. And the marble sound maybe a sticking lifter or partly blocked passage. I bought some Marvel Mystery Oil, since it has great reviews with stuff like this. Kind of hesitant on adding stuff to the crank case.

Is there anything else that I should consider? seafoam the intake, etc?

 

My Jeep had a rather strange, intermittent vibration at times. It occurred often after the rig had been setting overnight, but also just intermittently as I was driving along. It turned out to be a bad intake manifold gasket.

 

I'm unable to listen to the video at this point, but the jeep has never run 100% smooth, even new. It's always little, barely detectable, hiccups. What plugs and wires are you running? On the Seafoam- check out project farm on YouTube, he does good tests on seafoam and MMO. Headers- and particular reason for them? In the past, not in this jeep, I've had nothing but issues with headers so I tend to stick to factory exhaust manifolds. Have you tried moving to the tow tune to see if that changes things for you? I run that one exclusively and have for a long while.

Following though to see what comes out to be the issue.

 

"Lower 1/3 oil level on the dipstick"??

Maybe you are running the oil away from the oil pickup when you decelerate and running it dry. Try the same tests with slightly over full level.

2500 is ok, 3500 is hard work constantly on highway towing hence the heating in the back. Hood ventilation might help there. Did you install the heat isolater back on the manifold? Your video sounded like my 2007 5.9 Cummins Dodge did. I am not sure how much $$$ you can throw around but I would do the 2.8 Cummins conversion if I were you. Sounds like you do lots of trips towing. That's what I was going to do but ran into manual bellhousing adapter issues etc so went Chevrolet/auto.

 

Hi guys, thanks for the inputs.

She has not experienced any more studdering during this week. In fact, it only happened once. I think it would be easier to diagnose if it happens again. I have a Bluetooth ODBII adapter and will check the fuel/air trim this weekend. I think that should indicate if there was a vacuum leak, assuming the sensors are fine. If that shows nothing, I might add a new coil pack to my toolbox for when we go on longer trips.

"barely detectable, hiccups" yes, haha. I have not tried the other tunes but will try them with higher octane on the next fillup. I had the exhaust manifold replaced by a Jeep specialist, so I assume they know what they are doing, but I have no idea what they put on. I just went out and took a picture, and they actually look more cast to me. https://photos.app.goo.gl/oVHFK7DqfMBp7K93A

"lower 1/3 of the dipstick" below half, above 1/4 on the crosshatches, . I wish it would only do that while driving. The recording I took was parked in the garage with my phone resting on the battery (or fuse box, don't quite remember exactly). The engine was cold at that point, only running for a few minutes. Ever since I refilled it from being unreasonably low after 500 miles, 1200 miles ago, it is holding steady, ever so slightly above the full line. That itself baffles me.

Carquest premium wires (advance auto parts) because of the lifetime warranty and the reviews were not horrible. I want to say that the plugs are Champion Double Platinum, but I cannot find them in my online order history. I should probably pull them and see if they have been damaged by the heat. Here are some pictures of the cooked boots https://photos.app.goo.gl/mcpidYdd5vrehw6s6

The Jeep is more of our daily driver, with a side of towing and fun. It's not the best vehicle for the first two, but it's what we do. I wish, but a Cummins is not doable right now.

The engine itself sounds much better than in the video. I think my phone has an EQ built in to pick up speech better. The ticking is defiantly the fuel injectors, tested with my stethoscope.

It just occurred to me that it might be the passenger side cat making noise after the pressure is let off.

 

The "marble noise" is hard for me to hear, but the headers might be leaking at the gasket, changing the O2 sensor's reading depending on whether it's a vacuum (deceleration) or pressure. Unfortunately, typical problems with headers are leaks at the flange gasket and burning up plug wires.

I'd try going back to stock on the tuner first since that's easy and free. I'd also look at fuel trims with and OBD2 scanner during idle and decel, a vacuum leak would cause positive trim, but a big leak will set a code (+- 8 is fairly normal). The PCV might be sticking, essentially causing a intermittent vacuum leak -- a cheap fix to try. Doubting anything is wrong with basic engine mechanical since the symptoms are decal related.

Stay in touch, interested to hear how this turns out.

 

Thanks for the input!
I know it's been a while, but I wanted to post an update. So far the noise is still occurring.

Since I last posted, the noise has remained about the same. I had taken it to a Jeep specialty shop and they had it for a few days, but in the end they said that for the most part the engine runs great, but they could not pinpoint the noise as it is difficult to reproduce and to bring it back if/when it gets worse.

Now, I have noticed this noise for at least 9 months, 10k miles, and it has not seemed to have gotten worse, but it still worries me that when it does, it will be bad.

A few more tests that I have ran:

• Using a mechanics sethescope, It sounds like it is near the front/bottom of the engine.
• It doesn't matter if the engine is warm or cold
• Occurs between 650 (min idle) and 700rpm
• Usually only lasts a few seconds, but I have been lucky? enough to get it to go longer twice now (see recording below).
• Unplugging the sparkplugs 3/1/2 does not make a difference. (that should eliminate piston slap, wrist pins, and rod bearings, right?)
• When I unplugged 1, it sounded somewhat more prevalent (main bearing?)
• Timing advance is all over the place (in my 2 minute sample in closed loop, it was from 5.5-7.0. Scotty Kilmore says anything more than +-0.5 is a bad timing chain)
• I tested the timing chain by removing the cam position sensor and rotating the crankshaft. Has about 1/8" on the crank pully worth of slack, within spec (https://www.jk-forum.com/forums/jk-w...er-pan-353031/)
• Ran MMO the last 1000mi before the latest oil change (no difference)
• Oil and pan had no visible contamination (pan checked late last year)
• Switched to Mopar filter vs the wix xp (solved the cold start oil sound)
• Removed the SuperChips 87 tune for a month. Glad to have it back on!
• Checked under the passenger side valve cover and everything looked great
• Oil pressure is good as well.
• I did notice while the oil pan was off, that the rods slid along the crank, but felt tight in the other direction.

I found a few methods to reproduce

1. start the engine and let idle for 10-30ish seconds, will make the sounds for 2-5 seconds
2. with the engine running, press on the gas for a few seconds (2K-3K rpm) and after 1-5 seconds of idle, it will make the sounds for 2-5 seconds
3. with the engine idling, toggle the A/C on and off, 25% of the time, it might trigger the sound.

Here is the audio clip I prepared earlier. Listen closely at the cue markers near 0:14

This was an audio recording I made today. Got it aggravated as it lasted for quite a while. Listen for the marble / pinball machine noise. I placed the microphone on the front axle.
https://drive.google.com/file/d/1q39...ew?usp=sharing



Also some screenshots of fuel trims and such

 

From what you say my guess is the timing chain or tensioner especially with timing all over the place as there is a cam sensor that of course would be affected by slack chain or failed/worn tensioner.

 

Thanks for the reply, unfortunately the 3.8 does not have a timing tensioner. Also, the chain appeared fine when I tested it. I might try again later tonight.




Edit: I just remembered that we took the jeep to the beach a few months ago. The 11hr drive each way was fine, but while we were driving the road along the coast, 40-50mph for a while, I got a cat code. I pulled over and checked it. Then cleared it and it has not come back since.

 

Starter touching the flex plate? Maybe the starter solenoid isnt fully retracting and just touching the flex plate. Hard to tell from video bit it sounds similar.