Another spark knock thread... sorry

[kneedragger]

Hey Folks,

I bought a 21 JLU Rubicon w/3.6 last winter. It was a lease turn in with 11K miles on it. Same story, around 15K miles (this summer) I noticed the infamous spark knock. Occurs around between 1800 - 2000rpms, mostly on a shift between 3rd and 4th. Took it into the dealership, they couldn't replicate it and sent me on my way. Took it back to the dealership and took the service manager for a ride. He heard the noise and acknowledged it. They had the Jeep for 4 days and their conclusion... my Smittybilt rock sliders are rattling. I wasn't nice about that response but whatever. They told me if I take the rails off they will try to replicate the noise and go from there.

I've been running ethanol free 91 octane in it since I first heard the knock. I have run a couple bottles of fuel system cleaner through it and nothing. It seems to be getting worse as I'm now hearing it between shifts at higher RPMs. The Jeep only has 18K miles on it and I have power train warranty through 10/2024 but I'm starting to question the longterm reliability of this engine.

Is there anyone else having this problem with higher mileage 3.6 engines?

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[OldGuyNewJeep]

Record it so we can hear what you’re talking about.

 

[Old Jeeper]

Hey Folks,

I bought a 21 JLU Rubicon w/3.6 last winter. It was a lease turn in with 11K miles on it. Same story, around 15K miles (this summer) I noticed the infamous spark knock. Occurs around between 1800 - 2000rpms, mostly on a shift between 3rd and 4th. Took it into the dealership, they couldn't replicate it and sent me on my way. Took it back to the dealership and took the service manager for a ride. He heard the noise and acknowledged it. They had the Jeep for 4 days and their conclusion... my Smittybilt rock sliders are rattling. I wasn't nice about that response but whatever. They told me if I take the rails off they will try to replicate the noise and go from there.

I've been running ethanol free 91 octane in it since I first heard the knock. I have run a couple bottles of fuel system cleaner through it and nothing. It seems to be getting worse as I'm now hearing it between shifts at higher RPMs. The Jeep only has 18K miles on it and I have power train warranty through 10/2024 but I'm starting to question the longterm reliability of this engine.

Is there anyone else having this problem with higher mileage 3.6 engines?

NOT rare, my TJ 6 knocked so bad I could not even drive it on the freeway, city streets only.

What fixed it?

I added some hood vents to get the hot air out of the engine bay and I added a CAI and it all went away.

I am surprised you are having that in Maine??? Spent a lot of summer time up there and never seemed hot to me...

 

[kneedragger]

I'll try to get some better videos and post them. Like others here have said, it sounds like a chainlink fence is dragging under the front axle.

Our summers get into the 90s... and humid too. But I notice the knock is more prominent when I've been driving for a while and the engine is warmed up.

 

[m3reno]

I've been hearing some light knock under light load. I just increased the octane to 89 yesterday, so I'll see if that remedies the problem. These engines are definitely not low compression (11.3:1) and without the VVT would require higher octane. I'm figuring some VVT engines can adjust better than others.

 

[kneedragger]

Until I can get a good video of mine, here is a quick clip I scraped from the web. Turn up the volume and listen as the right curve marker appears through the windshield. Mine will make this same sound under slight load around 1800-2000rpm. Depending on how long it's held in that range is how long it will knock.

 

[kneedragger]

I did see in a thread on this forum that the culprit is the metal clamp that holds the O2 sensor wire on the driver's side manifold. I quickly removed it to no avail. I don't think it's a shield/clamp issue anywhere either.

 

[PatriotX]

It would be trivial for a tech to hook up a scan tool and see timing retard due to knock under load. No need to have a non mechanic try and listen for an intermittent noise.

Your ECU Will also log spark knock events. This shouldn’t be a guessing game.

You may wish to try another dealer.

 

[Willys41]

I had the same issue with spark knock on my 3.6
The first time I herd it was on a steep hill off road
What fixed it for me was installing a UPR oil catch can
It removes 98% of oil mist that would normally enter the combustion chamber degrading the air fuel mixture. I have not herd one ping after installing the catch can
What I liked about the UPR is it is easily removable if you have to take it to the dealer
Another upgrade I installed about two mouths ago was the RpmExtreme Jeep jl fan controller

http://www.rpmextreme.com/Product/311/Jeep-JL-PWM-FAN-CONTROLLER.aspx

It lowered my coolant and oil temps by 25 to 30 degrees and to my surprise also reduced the amount of oil that the catch can was collecting (less oil mist in the crank case)
On the left before RpmExtreme Jeep jl fan controller
On the right after the RpmExtreme Jeep jl fan controller

 

[Jeep Wick]

I did see in a thread on this forum that the culprit is the metal clamp that holds the O2 sensor wire on the driver's side manifold. I quickly removed it to no avail. I don't think it's a shield/clamp issue anywhere either.

Run 93 octane and I bet this goes away. I have the same issue when running lesser gas. It's a high compression motor.

 

[kneedragger]

Run 93 octane and I bet this goes away. I have the same issue when running lesser gas. It's a high compression motor.

Wish we had 93 around here. My best option is 91 ethanol free.

 

[kneedragger]

I had the same issue with spark knock on my 3.6
The first time I herd it was on a steep hill off road
What fixed it for me was installing a UPR oil catch can
It removes 98% of oil mist that would normally enter the combustion chamber degrading the air fuel mixture. I have not herd one ping after installing the catch can
What I liked about the UPR is it is easily removable if you have to take it to the dealer
Another upgrade I installed about two mouths ago was the RpmExtreme Jeep jl fan controller

http://www.rpmextreme.com/Product/311/Jeep-JL-PWM-FAN-CONTROLLER.aspx

It lowered my coolant and oil temps by 25 to 30 degrees and to my surprise also reduced the amount of oil that the catch can was collecting (less oil mist in the crank case)
On the left before RpmExtreme Jeep jl fan controller
On the right after the RpmExtreme Jeep jl fan controller

Catch can is ordered!

 

[Willys41]

I was running 91 octane at 4000 feet altitude and still had spark knock
After oil catch can installed no more spark knock

 

[mwilk012]

What oil are you using?

 

[alphawolff]

NOT rare, my TJ 6 knocked so bad I could not even drive it on the freeway, city streets only.

What fixed it?

I added some hood vents to get the hot air out of the engine bay and I added a CAI and it all went away.

I am surprised you are having that in Maine??? Spent a lot of summer time up there and never seemed hot to me...

Dude you can't compare a 20 year old straight 6 to the modern pentastar. I don't think they even share design elements. Like nothing is even remotely the same

That being said I'm pretty sure there's not only a PCM update for it but also a TSB to replace the PCV valve for excessive spark knock (especially when already running 91 octane)

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