Exhaust Drone

[Bobo57]

I don't believe it is MDS because I lock MDS out using manual mode. While driving, in traffic, it doesn't bother me but when coasting down hills off throttle, that is when it is the worst, whether in manual mode or normal including MDS.

I'll rig up a gpro this weekend and have a look at the valves. I am trying to stay away from the Z programing to maintain warranty. I just passed 3200 miles. My biggest concern about the vehicle is the transfer case and I don't want to give them any excuses. As for the lag you mention, I have noticed a lag, but I was contributing that to the clutch pack in the T-case. When I feel a lag, the engine still sounds responsive. Is that the lag you are referring to?

I've got a 23' and have zero drone, just a beautiful exhaust note when you get on it. Even with the valves open when I'm cruising on the highway it's quiet. With the valves closed it's quiet as church.
I'm betting there was a muffler design change on the 24' forward.

 

[Winston]

I've got a 23' and have zero drone, just a beautiful exhaust note when you get on it. Even with the valves open when I'm cruising on the highway it's quiet. With the valves closed it's quiet as church.
I'm betting there was a muffler design change on the 24' forward.

Something changed, that's for sure. I drove a '22, no drone complaints at all. My '24 is a different experience altogether.

 

[Canadian 392]

I've got a 23' and have zero drone, just a beautiful exhaust note when you get on it. Even with the valves open when I'm cruising on the highway it's quiet. With the valves closed it's quiet as church.
I'm betting there was a muffler design change on the 24' forward.

This confirms there is something seriously wrong with the exhaust on the 2024 model year. I drove a 2023 392 for my test drive and there was no drone either. I would have never bought this vehicle if the test drive with the 2023 had any drone.

This is all information I hope to communicate with Bob, Jeep's CEO. I have sent him multiple emails with a link to this forum thread, as well as my shop foreman's work order at the dealership indicating the drone to be loud and un-tolerable. my last follow-up email was earlier today.

 

[Canadian 392]

I am new here but not new to Jeeps. I had the 2.0JLUR, then JT Mojave, and now back to the Wrangler and without a doubt my favorite. I purchased a new old stock 2024 Final Edition which came with about everything, excluding the fancy roof top, but it did include the drone. I chalked it up as normal. After reading thought this chain, I saw the suggestion about using AI and learned a few things that I need to verify. I hear the drone most when I am off throttle and going through our neighborhood at 25-30 mph. I always drive with the "loud button" on but apparently that doesn't mean the valves are always open. Claude AI is theorizing that there may have been a change to the 2024 model year Active Exhaust Valve Programming. This needs to be verified, but it may be that when the off-throttle condition occurs, the DFCO - (Deceleration Fuel Cut-Off), the exhaust system is under vacuum instead of pressure. This completely changes the acoustic characteristics. If your active exhaust valves close during DFCO (which they might, even in Track Mode), you're creating a resonance chamber at a very specific frequency, ~72 Hz fundamental with strong 129 Hz 2nd harmonic. I am attaching the Claude AI details in a pdf document if anyone is interested.

@ ruscopin,

Excellent Work!

I think you really narrowed down the most likely explanation for the drone issues. The Deceleration Fuel Cut Off (DFCO) must be activating when completely off throttle or nearly complete off throttle while in the 1400-1900 RPM zone.

*The drone is never present while accelerating through that RPM range, only when I am completely off throttle or nearly completely off throttle in that RPM range.

* Once DFCO is activated, this would create colder/air vacuum in the exhaust system to the cylinders, instead of positive hot exhaust flow out tail pipes because the injectors turn off with DFCO in that range. I think this explains why there is no drone at all when the engine is cold for the first few minutes.

*There must be a parameter in the DFCO settings that only activities DFCO once the engine is already warmed up. At a certain operating temperature, the DFCO is activated once certain parameters are met: namely being in the 1400-1900 RPM zone AND either being completely off throttle or nearly off throttle (with very mild throttle input, even if its like only 2-3% throttle). The system still needs to have some fuel injected in our drone zone to keep the exhaust gases hot and exiting with speed through the tail pipes.

*Otherwise, when DFCO is active (zero fuel being injected), it creates the perfect storm of slower flow and or vacuum, cooler air, and excites the bad resonant frequencies in the exhaust tubes and vehicle structure producing that loud low frequency boom/drone.

* This is likely the difference between the 2024 model years, and previous years, which owners report no drone. Engineers likely changed the 2024 DFCO settings for emission standards, creating this problem.

Has anyone here unlocked their PCM and using HP Tuners or other programs that provide access to the DFCO settings??