Got my own home-brew version of a remote-controlled switch sitting waiting for warmer weather; will post photos & instructions once I get it done

 

Just look at the function of the rear muffler system. There is a mushroom valve on each side of the muffler. It is a butterfly valve that is vacuum operated. This is for the 2010-2015 XKR and I don't know if is the same for the 2006-2009 XKR or even the XK. These 2 valves are normally open and will close when you start the car. If you listen you can hear the exhaust note change after a few seconds when you start the car. Also when you accelerate after 3500 rpm the valves open. This gives the exhaust a free channel to flow and make more noise. now the function of fuse 19 is to operate the vacuum valves which need 12V to function and close. So if you remove the fuse 19 these valves will not close and stay open . Now if you press the dynamic mode it opens these valves as well as changes the suspension and gearbox settings . So the net is fuse 19 lets the valves stay open all of the time if removed.

 

The 4.2L XKR is also an 'active' system and functions the same, electrically controlled vacuum pump to close the valves (removing the fuse prevents the pump from running, and the valves stay open), all based on RPM and throttle angle.
The XK is different, in that it is a passive system, and the valves are normally closed, and open based on exhaust pressure only (i.e. step on the throttle, and they open).

 

I only notice the exhaust go quiet as I pull away on my '07 XKR which matches what the workshop manual says because the table in that says that it should be open between 500 and 1000 rpm. The 5.0L manual actually says the open range for those is 700-1100.

If the engine is cold then the revs could be over that for a short period but I would expect the valve to be open at idle on a car with a warm engine.

 

Unless you have something different that is not the way the exhaust system works on the XKR. Also could you print what the WSM says because I think you miss interpreted it. With the engine shut off the valves are OPEN. When you start the engine the valves start to close as the vacuum increases so it is louder and then quiets down . The valves stay CLOSED unless you are going WOT and then will open at 3500 rpm. It has nothing to do with cold or hot engine. It's a pretty simple system.

 

So to be clear, on a 2012 xkr pulling fuse 19 shouldn't be done at all as I get the exact effect by initiating dynamic mode? unless I want open exhaust without the other DM features.

 

Fuse 19 is for the vacuum pump that operates the exhaust valve. The valve default with NO vacuum applied is OPEN. It takes vacuum to shut it via ECU command. The ECU commands the vacuum pump in various modes. If the pump has no power, the valve stays open regardless of ECU command. It has no effect on ECU operation ie. "modes".

 

Correct

 

Ngarara is correct the valves in the outer exhaust pipes are set in the open position upon start up then close as soon as the throttle is pressed

Once the rpm reach either 3500 or 4000 (sorry I forget) they fully re-open

All pulling fuse 19 doesn't is leave them in default mode (open position) and much to popular belief you don't lose torque down low , I've had my vehicle on the dyno and nothing essentially changing with them in the open or closed position

One thing I didn't get a chance to do was to see how much an x-pipe improved my hp I revert back the stock set up as it was too loud with 100cell cats

 

Yep I can confirm that, I have a 2008 XKR Portfolio and pulling fuse 19 definitely works.

 

Almost. The Workshop manual says

Later, it says:

(My emphasis). So, you start up, the car does its initial rev and fast idle, then settles down to a slow idle. The active valves are open all this time, but from 5 seconds after power up the system is ready to close them as soon as the ECU tells it to.

What isn't clear is the exact conditions under which that command is given. Yes, in the manual it says:

It doesn't mention Dynamic Mode at all, but empirical testing shows that the valves stay open then too. And it also doesn't say what the rules are in Park or Neutral. Having blipped the throttle in both states, it definitely sounds pretty loud, which would suggest the valves are open (and that lines up with the idea of keeping them open on startup to make the car sound good). But I can't really do a comparison against Drive without a rolling road.

 

Ok lets talk about the 5 seconds. When you start the car the ECU counts to 5 seconds and turns on the vacuum valves which CLOSE the exhaust valves. Nothing to do with rpm but just time. In Dynamic mode the exhaust valves OPEN until you shut it off. Same as in S mode . Last at around 3500-4000 rpm the ECU OPENS the valves . In park or neutral if DM is pressed they are OPEN or if you rev it to 3500 rpm they OPEN otherwise they are closed.

 

This is the table for the 5.0L I am referring to. It implies that at idle the valve is open and will close once the revs reach 1100.

I took fuse 19 out shortly after I got my '07 XKR but did put it back in briefly to remind myself what the difference was in sound and as mentioned I can hear the exhaust note change to be almost silent as I start to pull away but not before.

This is from the Technical Intro Guide for the '07 XKR:

The active exhaust valves are operated in response to
engine speed and throttle angle; the valves are normally
open until a vacuum is applied. At start up, the valves
are always opened to give an enhanced sound. The
valves are open at idle, close at 1100 rpm, re-open at
3000 rpm and remain open until full throttle.

And this is from the one for the 5.0L:

XKR 5.0L SC Active Exhaust System
The position of the exhaust valves depends on engine
speed, throttle angle, and transmission operating mode.

At startup, the exhaust valves are always open to
enhance the exhaust sound.

When the transmission is in the manual (sequential shift)
mode, the exhaust valves are permanently open. When the
transmission is in the normal or sport mode, the position
of the exhaust valves depends on engine speed and load.

 

Sounds correct. Stand behind the car and let someone start it . Listen to the outside tips and you will hear when they close. Around 5 seconds which may be 1100 rpm. As I said after 3500 or 3000 rpm they open up but when you settle down in 6th gear and are doing 60 mph they are closed. With the top down I can always tell when they open or close.

 

Sorry, but no - after 5 seconds the ECU turns on the pump to create a vacuum and supplies power to the valve solenoids, but that doesn't move the valves. Everything's powered up & ready to go, but nothing changes in terms of the exhaust flow. The valves are operated by the ECU providing a path to ground for the valve solenoids, i.e. after 5s the solenoids have a power supply, but current doesn't flow to actuate them until the ECU provides a ground to complete the circuit. As you say, that only happens in specific RPM and throttle-opening ranges, and not at all in Dynamic Mode or manual shift.

And "same in S mode" is also incorrect:

But it doesn't say what happens in park or neutral. My unproven assertion is that the valves stay open so we can show off & make loud noises, in line with the way the valves are open on start-up to "enhance the exhaust sound". Once I fit my remote control, I'll be able to switch the vacuum system on & off and test that theory.

 

I'll have to go time it but I can hear and feel (put your hand over the outside tip) the valves close shortly after start up. I can have someone rev the engine up to around 3000rpm and they are still closed. I press the DM button and they open. With the car on the lift I can watch the actuator move at start. With the car in idle and the DM off go put your hand over the end pipe and compare it to the pipe next to it and the pulse difference lets you know the outside one is closed. Rev it up over 3500 rpm and the valves open and then close when the idle goes to normal. I think we have worn out this topic.

 

I guess the 4.2L's act as per the table in the workshop manual and the 5.0L's don't then. I put my fuse back in this morning as it wouldn't hurt to give the vacuum pump a bit of an exercise anyway and as mentioned before I can hear the exhaust mute a I pull away from lights, etc.

With an able assistant I have done as suggested and put my hand over both exhausts at tickover. You can feel air coming out of both. When the revs rise above 1,000 I hear a ratchet noise and the outside exhaust pipes close. When the revs drop back to tickover they open again.

 

I can only speak to the 5.0 SC car as that is what I have and experienced.

 

OK here is the best I can do. Took the car down to go play golf today. It was 68* in the garage so I got out my stop watch and proceeded to start the car. Engine went to 1250 rpm and the exhaust ran open for 6 1/2 seconds before they closed. Engine idle dropped in about 20 seconds to normal idle. Got out and felt the outside tips and hardly any pressure while the inside tips were at an appreciable pressure. Went in and pressed the dynamic mode and no change in exhaust not at idle in park or neutral. Then I put the top down as I normally do when I take the car out of the garage. Backed out and drove away in normal drive mode. Got out to the parkway and went WOT and the pipes blared out at between 3500-4000 rpm. Then settled down at normal 60 mph driving speed in 6th. Press DM and heard the difference in the sound at 60 mph. So this is with my 2012 XKR with factory active (X) exhaust.

 

That sounds pretty conclusive - thanks for doing the test.