The electronically-controlled bypass valves exist on both the 4.2 & 5.0 XKRs - non-SC cars have a simpler mechanical system. The XKR's valves stay open at low RPM and above about 3800; 4.2 & 5.0 are different, and it also depends on throttle %. Manual-shift or Dynamic Mode (5.0 only) will lock them open.

As Bruce says, if you want the noise without the hassle of manual gear changes or the firmer ride of Dynamic Mode, pulling Fuse 19 is the solution.

 

When aftermarket exhausts are fitted such as elite that have no valves fitted what happens to the black tubes that supplies air to the vavles on the original box are they blocked.

 

I put my fuse back in yesterday after about a month out. It was deffinetly more out there but I didn't like it driving with the top up or on the highway. When I put the fuse back in it went back to normal.

 

The car's noise always sounded a little fake to me. It sounds much more "real" without fuse 19 in. I love the sound now, especially with the roof down.
It does sound a little more "in your face" but in a good and still "appropriate for the car" way. If you listen to the old British sports cars (triumph, spitfire etc) it sounds very in-keeping with them.
The best part is that I can also now hear the engine enough to use the paddle-shift appropriately without having to also look at the tach. I've always been used to shifting "by ear". The fact that I couldn't hear this car enough to do that, bugged me before.
I don't think I'll ever put mine back.

 

That is the bit I was querying because only the 5.0L Workshop manual mentions manual shifting affecting the valve so I wonder whether it is purely revs and throttle angle that affect the valve on the 4.2L's?

There is no mention of it in the 4.2L XKR technical guide either.

 

I happened to luck out and have the active exhaust which is the same as the XKR-S . It has the X section in the front so I don't know what the 4.2 or the standard 5.0 XKR exhaust with the center silencer sounds like. As for mine it is just the way I like it. In normal mode it is quiet with the top up and a slight growl with the top down. If I get into the go peddle it sounds great as the system opens around 4K. If I want the open pipe sound I hit the Dynamic button and it sound great while in the lower gears. I think it is a great balance for fun cruising in town but quiet enough on a long journey to not bother my bride.

 

There's no mention of Dynamic Mode opening the valves in either workshop manual, but it does. I suspect the full specs of how the active exhaust operates just aren't documented.

 

True, it will be interesting to find out for certain though so I will put my fuse back in for a bit and see if I can tell the difference. It is nearly two years since the fuse was last in but the difference was quite obvious when it was taken out.

 

Wow, I had forgotten how quiet the XKR is with the fuse in. I drove most of the way to work in sports mode and using the paddles and the car has turned from a roaring tiger back in to a purring ***** cat. I can confirm that the omission from the documentation is correct, using the paddles on a 4.2L XKR does not open the valve!

You can hear the exhaust mute as you pull away from rest and as I don't tend to get over 3,000 revs on my commute to work it didn't make its presence known much. With the fuse out I can hear the exhaust echoing off the surrounding houses as I cruise around the suburbs at low revs. With the fuse in there is hardly any sound. It looks like the 5.0L therefore gives you a few options for hooligan mode without needing to pull the fues whereas the 4.2L is all or nothing.

At least I know my exhaust valve still works but I don't think it will be used again whilst I own the car. The fuse will be coming out again tonight!

 

Interesting! Another piece of info to file away. There's an earlier thread that talks about installing the Mild2Wild remote-controlled fuse bypass system so you can switch the system on & off at will:

https://www.jaguarforums.com/forum/x...-valve-102942/

The Mild2Wild is designed for a Corvette, so may need some mods for the Jag as it did for the Ferrari mentioned in that thread.

 

I wanted to try this and I removed fuse 19 on my 07 XKR. I do have to say that there is a definite difference on the exhaust sound and it's sounds so good!
I was just wondering since this is an old thread... has anyone experienced any long term effects/damage? or anything I have to watch out for? Thanks!!

 

The only effects you might see are dirtier exhaust pipes...at least for the ones that used to close with the fuse in.

Personally I think even without the fuse the car is too quiet!

 

Thanks!! Maybe because I live in downtown Philly with the tall buildings and narrow streets the sounds tend to echo and magnify. You definitely know when this cat is coming down the street!! its a beautiful thing!

 

So the question is when I collect my car Friday do I remove the fuse at the dealer or wait till I get home?

 

Drive it home first, so you have a baseline for comparison - also, dismantling your car on the forecourt might send the wrong message

 

That can tell though. I pulled the fuse as soon as I got it and when I went to my local Jag guys to check the car they commented on the mystery of the missing fuse, nudge nudge wink wink...

 

I pulled this shortly after getting the car but had no effect until I installed a new CAT - active exhaust didn't work while in need of a new CAT. Now other CAT is bad but active exhaust still works? Have others had early OEM CAT failures - honeycomb at front becomes loose? 2008 XKR Portfollio w/ only 13,0000 miles. 15/24 MPG

 

What are the symptoms of that?

 

The only downside I've heard mentioned is that the valves can stick in the open position after an extended period of time, or possibly the vacuum pump seals deteriorate through lack of use - anyway, basically, the system stops working. So, when you put the fuse back in, it has no effect. It may pay to put the fuse back in occasionally, just to 'exercise' the system & keep it working. Maybe do it when you send the car in for service.

 

I just fitted a Mild2Wild remote switch to my XKR - Only modification required was a change to the earth fitting (2 minute job). Now it purrs like a kitten when the switch is On, and growls like the beast it is when the switch is Off. I hear they have added a button to the F-Type to achieve the same effect.