Engine noise.....
JK Enthusiast
Joined: Aug 2011
Posts: 436
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From: Lima, ny
Originally Posted by JKlad
I know exactly the noise you are talking about; only the 6-speeds make it, it comes from the tranny/clutch setup, & is completely normal. Many people confuse it with spark knock but it is different.
When you take off from standstill in 1st at low RPMs under load & give it some gas it makes a raspy, rattling sound like you're driving on gravel for a second or two until the RPMs rise. Very different sound to spark knock, rattling cats or loose heat shields. If you have the transmission in neutral and rev the motor from idle you will also hear the noise momentarily (easier to hear if you're parked next to a wall with the door open or window down) until the flywheel speeds up enough the relieve the load on the clutch and transmission. If you release the clutch in 1st with the motor at idle and let the computer controlled anti-stall automatic throttle start the Jeep moving forward you will also hear it, particularly if you are going up an incline at idle using the anti-stall feature (and this sound will be prolonged as long as you don't touch the gas & keep the revs low).
I hadn't heard this sound on previous manual trans vehicles I've owned in the past so I took the service manager for a spin when I had it at the dealership for it's first service so he could hear it. Completely normal apparantly, & when I doubted him he started two brand new '09 6-speed JKs on the lot and revved them in neutral and they both made the exact same noise. He claimed it's the pressure plate vibtaing the clutch disc springs under load; don't know if it's true, but the sound definatly comes from the clutch/tranny if you get down under the Jeep and listen closely when someone revs it. Not sure whether the 6-speed CRD diesels make the same sound, as they have a different clutch setup with a dual mass flywheel and are generally noisier anyway at low RPMs so you mightn't hear the sound anyway.
i've got 65,000 on my jk 6 speed...that's definitely a lot of the noise you hear...to confirm try just revving the engine slightly with it in neutral..then try in neutral with the clutch depressed...you will notice a difference in noise reduction.
Also try putting it in 4 low and you will notice the sound may be completely gone or at the least not as loud and doesn't happen for a long...the change in gearing puts less stress on the tranny, pressure plate and associated components...I personally think it's more of a throw out bearing rattle but either way I would guess it's transmission related but nothing to really worry about, it's just rather annoying. I've had a gmc p/u, a Plymouth breeze, and a Pontiac vibe..all of them had this noise to some degree or another and I found the throw out bearing to be the culprit most of the time..my breeze had over 240,000 on it with the rattling starting around 100,000 and it still ran fine until it was wrecked.
JK Freak
Joined: Apr 2011
Posts: 847
Likes: 0
From: Texas
pull the plugs and check the gap. you can also install a better coil and wires - look at performance distributors screamin demon coil and livewires.
JK Freak
Joined: Apr 2011
Posts: 847
Likes: 0
From: Texas
JK Freak
Joined: Apr 2011
Posts: 847
Likes: 0
From: Texas
true, but it should diminsh. you can tell quite a bit from the condition of the spark plug, I would still pull them, check the gaps and see how they look.
depending on the mileage, they should all have a similar light whitish tan color to them.
depending on the mileage, they should all have a similar light whitish tan color to them.
JK Freak
Joined: Jun 2011
Posts: 534
Likes: 0
From: Whittier, CA
So I got a new 2011 JKU Rubicon, 6spd with about 2000mi on it. I changed the oil at 1000mi to conventional Valvoline 5w30 with a Fram tough guard filter. Vehicle is stock. Idling sounds fine, but when you press on the gas to go it almost sounds like a small diesel engine under the hood. Besides that it runs great, just sounds funny. Any thoughts or is this normal? Should I switch back to 5w20? Thanks.
Second, ditch that FRAM oil filter and never mount a FRAM on anything unless it's a FRAM HP1 series for racing applications.... for several reasons. The major concern is dry starts. I ran FRAM filters for 25+ years and found anti-drainback valve problems with FRAM filters on my 1991 4.0L HO. Therefore I've never bought a FRAM since. I would just stick with Mopar or install Mobil 1 or K&N filters (both made by same manufacturer).
Third, I don't think the above are contributing to your funny sounds...
However, I would run the octane that the operating manual indicates you should run. I would try running a bottle of Chevron Techron fuel system cleaner and see if that helps... at 2,000 miles it shouldn't be detonating. Where are you buying your gas? Arco, BP?
What were the first 1,000 miles like? ...
If the pressure plate is rattling then you may have to live with it ...
.
Last edited by m998dna; Sep 25, 2011 at 12:07 PM.