“Also if the supercharger "bypass valve vacuum actuator" is not working and stuck open you will have a very slow XKR”

Saw this on another thread quoted from XKR-DAY. Did not want to hijack that thread so starting a new one.

Can someone tell me where this is located and how to tell if it is working properly? I searched the forum but probs missed it.

Thanks

 

Neil,

The Waste-Gate is located under the S/C in the intake column....You can pull the little Rubber Hose off the S/C on the Right side and if you lose power you'll know the Waste-Gate is working or not.....If not, you have to remove the S/C to get down to the intake Channel so you can clean -out the Waste-Gate....Sometimes it gets Oil and stuff in it!
Also, there are 4 little Bolts that hold down the Hat....Look real close and you will see they have Rubber Washers....some times those little washers need replacing and if they are bad…..When you replace them! It will WOW! you with power. The Hat is the Top of the S/C with V8 stamped on it...

And another thing to look for is the Duct Seals and Plates...If the Seals are slipping and leaking....You need to go to Eurotoys.com and order one of their sets....They are the best made!

Billy Clyde in Houston

 

Found an engine picture on eBay. Like BC says, it is buried in there pretty good.

I don't have one like this any more, but as I recall, you can take the throttle body off and get to it.


The valve itself is a simple butterfly thing with a vacuum actuator. High vacuum pulls it open, low vacuum (full throttle) closes it by a return spring.

If it were stuck open, you would have very poor power regardless of throttle position. The supercharger would never make any boost at all.

 

Thanks to you both for such detailed and helpful replies. In-laws in town this week so it will be 10 days or so before I can check it out.

This is is a sweet ride but a lot of things have to work exactly right for it to go fast. Steep learning curve. On the plus side I swear the more I drive this car the better it runs.

Thanks again

 

funracer,

Better watch out for those Florida Highway Cops.....

BC

 

It's probably not failed - what problems are there?

 

6.2 seconds 0 to 60 mph is the best I can get. Sport mode ON, top up, half tank of gas etc,

Car is fast-ish but not 5.2 fast if you know what I mean. Feels heavy to me but I have never driven another
XKR so no reference.

No performance related codes or dash lights. Some BPM codes I believe are associated with my amputated
Valet system but that is it.

Only owned it a about 3 months. Changed engine oil, adjusted the throttle cable, changed S/C oil, removed the airbox butterfly valve bc I could not verify it was working properly (this did not change my 0-60 time at all btw). Next on the list is coolant flush then I will get to the bypass valve.

Keep in mind I am hand timing with a stopwatch so maybe I am am getting it wrong somehow. Or maybe these cars just lose
a second after 65,000 miles. Is it normal that I cannot break the tires lose when I mash the throttle? New P-Zero’s.

Still a beautiful cruiser but I just feel like it is lacking something under the hood.

 

Keep in mind that these XK8s and XKRs are essentially GT cruisers, not race cars. So many modern vehicles of all designations can outrun them in the quarter mile now. Just enjoy your XKR for what it is....

 

the most common failure of the bypass valve is broken vacuum lines.
past that you should clean its blade to because it gets just as nasty as the throttle body. too verify operation. Access the blade, apply vacuum making sure the valve hold vacuum and not leaking internally and that the blade moves freely and fully seats.
if you want to really wake up the car install a lower and upper pulley. Totally changes the car. And yes IMO it is and always has been a dog from a stop even with trac off because that's the way jaguar tuned the car. Now do that in a Stype R and you'll really light em up good. Why they did that with the 4 door mid size sedan and not the 2 door XK is beyond my understanding.

 

Funracer,

Brutal is right, you should check all these things, Vacuum Hoses but the only one that creates a problem for the Waste Gate is the little one I told you about....Check it and then check the Rubber washers that hold down the Hat! I've never had a problem with my Waste Gate but you don't know what the last Owner might have done.....Before you start changing Pulleys, you want to make sure the previous Owner didn't already do that.....But as Brutal says, if you want power you will need to change the Pulleys...Do some measuring, if they are stock Pulleys you can go to one of our Sponsors, like Eurotoys.com. They have everything you will need to set it up with the Hot Pulleys. This will make your XKR really come to life....It's surprising the difference it makes!

BC

 

Are these the bolts (yellow) and hose (red arrow tip) you are referring to? Excuse my poor artwork.

 

If 2004 has 2 fuel pumps like the 2003 and earlier, are they both working?

 

Only one pump. 55 psi constant from OBD read out

 

Neil, Yes, also the Hat has a rubber gasket around it too!...If they start leaking, you will lose a lot of power...Only way to check them, I think, is to take it apart and replace the gaskets......Check for the parts first...you want to have them handy.....The Hose goes to the Fuel Pressure Regulator on the Front right ...

Billy Clyde

 

Chirpy and Funracer,

the 4.0 Liter Engine was the only Engine with 2 Fuel Pumps....All 4.2 Engines only have one and it is in the Gas Tank...

Billy Clyde

 

I have also added a tee on the passenger side of the supercharger and temporarily connected a boost gauge to make certain I was getting full boost without taking everything apart. I believe full boost is about 11.5 psi. Can't get to the car right now to take a picture of the connection point.

 

Which years of the 4.2 SC do you mean? All the 4.2 SCs I know have 2 pumps (both in the tank)...

 

If Billy Clyde's understanding is the same as mine, it would be all years of the 4.2 SCs. This is the first post that I have seen to the contrary. I would welcome any enlightenment.

 

I just looked in the parts catalog for a 2004 XKR and only shows one fuel pump in the tank. XK8 also shows one pump but different part number than XKR.

 

Wouldn't be the first time either a catalog was wrong or someone missed something.

One pump does not supply enough fuel for an SC 4.2 at WOT.