I need a specific, detailed explanation for why pulling fuse 15 from my 2022 P450 made such a drastic difference. I finally decided to remove that fuse because of comments I've read here, but to be honest did not see how it could make any difference since the exhaust is switchable and I thought that being the case open was open and that was it.
But, wow, pulling that fuse released a beast I didn't know existed--louder exhaust at low speeds and the old crackles and pops with the ability to feather the gas pedal to accentuate them. I couldn't be more pleased.
Anyone know why the big change?

 

The switch probably just sends a signal to a module whose software decides what to do with it, and when. Pulling the fuse takes the decision out of the module's hands (or code). Just a guess - prove me wrong!

 

Perhaps it's just in your head.

I also pulled fuse 15 soon after I bought my car and never looked back. Why anybody would drive the car any other way is beyond me.

 

Fuse powers the module that fluctuates the opening and closing of exhaust valves. No fuse means it can't control the valves and they are wide open all the time which means all the sound gets through. Apparently pressing the exhaust button sounds different in normal vs dynamic so it's there's something more than just a binary setting of opened and closed. My guess is that the valves are not just opening and closing but the software is constantly adjusting them to limit sound. Why you ask? Probably for noise/sound regulation laws in some country.

What I also wonder is if that module or the software's failure to control it also has side effects. Maybe it does something additional for the pops and bangs because otherwise why would you not hear it when the valves are closed, they should still be there but muffled/reduced. You never know, there's always that one crazy engineer that puts an easter egg in the code, if fuse 15 is gone make the exhaust go hog wild.

 

Do you mean it is louder than it was before when you switched it to loud?

I cant do mansplaining as I might not have it right, but I did similar in my XKR which didnt have the button, so here goes (and someone will correct me if I'm wrong):
1. there are some valves in the exhaust system;
2. the exhaust valves default to a closed off position making it quieter;
3. when you start the car, they open for about 10 seconds or so (just a guess) which gives the big startup bark;
4. then the valves close, quieting the car down;
5. when you get to about 3500rpm (just a guess again), they open up and it gets plenty louder;
6. if you put the car in dynamic, or push the binoculars button, they open up at any rpm and it gets louder.

If you look at post 4 in this thread, it shows it. As you will see, generally the exhaust is going through the middle 2 pipes, but with the valves open it goes through the outside pair as well https://www.jaguarforums.com/forum/f...xhaust-212060/.

 

I got my 2016 R in September last year. The "active exhaust" button didn't work, so I had it checked at the dealer. Seems someone had removed fuse 15. I think I will be putting the circuit on a switch if just pressing the button is not the same as removing the fuse. I do want it to be quiet when I want, but I do love the way it sounds now and don't want to lose that option!

 

This person tapped the fuse to a wireless switch. The whole setup cost them around 30 bucks to build. Post #17 in the following thread https://www.jaguarforums.com/forum/f...e-43-a-213500/

 

Perfect, thanks!

 

As others have stated, pulling the fuse keeps the valves open 100% of the time. Even with the exhaust button on and in Dynamic Mode, the valves aren't open 100% of the time. The two programs (open/closed) plus Dynamic Mode change the threshold for when the valves open and for how long. You will notice it is much louder on startup because in any other mode the valves will close once vacuum pressure builds on cold startup--even with the switch on. You're hearing it with the valves fully open. And you'll notice a difference on mild to moderate acceleration in the 1K-2K RPM range because the valves are normally closed in most other modes and acceleration positions at that range, but not when the fuse is pulled.

I set up JagBass's remote module (even using the center HomeLink button to activate/deactivate it) and now I have the best of both worlds--switchable exhaust when I want it and fuse pulled when I don't, all from the comfort of the driver's seat and even while underway.

 

Thanks to everyone for your input. Your comments have confirmed my suspicions on the varible open/close question, but I suppose I had originally and inaccurately assumed that the active exhaust switch opened the valves completely and they stayed open.
In any event I love it!

 

Never overestimate the power of an apparently binary signal sent to program code!

 

I experimented with removing fuse # 15 shortly after buying the car. Yes, it responded differently than just pressing the button on the console to open the valves. I live in the mountains and when on a downhill stretch with the transmission in the manual mode and holding the gear to get some compression braking the crackles, bangs and pops were very noticeable. There was one time I passed a group of bicyclists and as I let off the gas the exhaust went off like an MG42 machine gun and I thought they were going to pile into each other as they were looking back at me. It was kind of fun but I ended up putting the fuse back in as it was a bit too much of a good thing for me.

 

Thunder Dump has it right, as usual. I use this kit (he has an F-type version) to switch F43 in or out with a key fob. (F43 powers the active exhaust vacuum pump on older models.)
https://www.cccharger.co.uk/on-site-...st-remote-unit

 

https://www.cccharger.co.uk/on-site-...st-remote-unit is no longer an option : (

 

Does anyone know whether having the exhaust valve open full time (fuse removed) negatively impacts the cat converter life expectancy or warranty?

 

Since the system is designed to run with the valves open, and seeing as there is no warning in the manual (or anywhere else) about limiting the use of the open valves, this is really a non-issue. The valves are far downstream from the cats so the only thing having them open does is cause a little less backpressure in the system, which certainly won't hurt the cats at all. If anything, improving exhaust flow (and therefore removing any raw fuel/fuel vapor faster from the cats) should be a benefit and not a detriment. It certainly doesn't violate the warranty as the system is designed to run in this configuration.

The only long-term consequence that *might* result from this (and this is just conjecture) is the valve opening/closing mechanism could corrode over time from lack of use and the valves could get 'stuck' in the open position mechanically. However, this is still highly unlikely and if it is that much of a concern you can reinstall the fuse every now and then (or install one of the remote relay setups) to 'exercise' the valves on occasion. You can also reinstall the fuse before any dealer visit and quickly restore the car to its normal operation.

 

There are more pops and bangs with the fuse pulled (vs. OEM programming). I can't help but think these could be detrimental to the Cats... But who cares, it sounds so good!

 

The pops and bangs are not a result of the exhaust--they are a result of the ECU programming that dumps raw fuel into the exhaust on overrun. You*hear* more pops and bangs because the resulting system is louder at all times (especially in the lower ranges where normally they would be muffled blats), but pulling the fuse doesn't cause the car to make any more than it did before. It is a single circuit whose only purpose is to operate the valves.

 

For my first 18 months of ownership, I was unable to distinguish exhaust valves open from closed.
Eventually JLR agreed and replaced the exhaust solenoid(s).
Apart from a few pops in sport mode, it was only modestly louder with the exhaust valves open.
Today, I removed F15. What a difference!! It sounds more like the used V6S I test drove in 2020.
Back to the future!!

 

A little pop and crackle is good for the ears, to much is bad for the engine.