Hello,
My apologies in advance for any stupid questions, I just don't know very much...
Please help me understand this..
A SC produces more molecules of air available for the exploration chambers. Does that mean the vacuum is the same as for a N/A engine but more air (being that it's compressed) enters on the intake stroke?
Is the SC inducing air into the head of an engine is also reducing vacuum? I've read the S/C produces 15psi on average, what should be the vacuum value in the XKR SC engines ?
Finally, shouldn't more fuel be vacuumed in as well to compensate the extra air?
If somebody could explain with some number and also what number should I see in diagnostics tools for an healthy engine, that would be a great help.
Thanks!!!

 

Your engine has problems I’m guessing. What are they ?

Z

 

The only device on our cars that is vacuum operated is the brakes. When the engine runs driving the wheels there is pressure in the inlet manifold BUT when you take your foot off the gas the throttle butterfly closes ,the charger has no air to suck so you get a vacuum which works the brakes. The fuel added is determined by the oxygen sensors indicating to the ECU too rich or too lean so adjustments are made.
You should be looking at the fuel trims which should be only small numbers + or - as they are a deviation from what the manufacturer thinks is normal.

 

Thanks. I'm just trying to better understand the mechanism. I have concern with the performance, my 0 to 60 sucks, taking off from 0 is so slow compared to my other 400 HP/400lb ft car (a n/a MB).
I have no error codes or engine light, smog passes and acceleration from 30mph is great. But just like a tank from 0 to 40mph..
Thanks!

 

​​​​​​ Short and long trims are good.
How do air and fuel get in the chambers without vacuum? From pressure from the S/C induced air?
Checking fuel trims is fine but that doesn't explain how that works with the SC and for the air flows to me

Thanks

 

The air is pushed in by the SC as well as the pistons sucking.
I have found that when re connecting the battery you must move the throttle through its range with just the ignition ON or it is sluggish as you suggest.
You must also use the S button if you want to go like **** off a shovel.

 

Not sure what year car, but have you checked for throttle cable slack? If applicable it's an easy adjustment and can make a world of difference.
Might pay to check throttle % as well if you have a code/data reader suitable.

 

^^ This. Adjusting the throttle cable slack is usually a necessary task on these vehicles as the years go by. It brings the acceleration back to life....

 

Don't forget to use Sport mode, like Pistonbroke said, otherwise I believe you will be in second gear, not first.

 

I very rarely use sport mode and my XKR is pretty damn quick off the line

 

The Eaton supercharger on Jaguar XKR is actually not a compressor! It is more like an air pump that pumps more air into the engine. When more air are being pumped than the actual displacement of the cylinders, it creates pressure (boost).
At closed or part throttle you will get vacuum in the intake and this vacuum is used to hold the bypass valve in the supercharger open, meaning that the air will bypass the supercharger and go directly from the throttle body to the intake.
When you opens the throttle the vacuum will disappear and the bypass valve closes, forcing the air to enter the supercharger.
Up till then the supercharged engine will operate and work just like an naturally aspirated engine.
You will not measure any difference in vacuum.
The only place you can measure actual boost, is in the vacuum hose that goes from the supercharger to the fuel pressure regulator. You will se it on the right side of the supercharger outlet, just behind the big air bleeder/filler plug.

 

Thanks a lot, that was really enlightening!
I would love to talk about it a bit more as I have a couple more questions, city l could we have a chat on on the phone? I can be reached at myasianvpn@gmail.com (hope that email will go through) or private message (dunno how it works here), then we can take it from there.
In any case, I really want to thank you for your help, that was nice to take the time to explain in details. If there's anything else you think I should know about any of this?
Thanks!!!

 

It's an 04 (first half of 2004, so x100).
Have used advanced scanners, no codes. Does anyone know how to get the transmission to re-learn shifts on these MY? I've seen tutorials for the 4.0L but different trans..
I'll have to check the cable..

Thanks.

 

There is also a coolant pump for the charge coolers to keep the intake air cool. You should make sure that is running.

 

I've sent you a PM

 

I'll check. I wasn't aware of there was one. You're not talking about the electric air pump are you?
I would think that if the supercharger overheated I'd have other issues no? Is that what you're suggesting?
Thanks.

 

It does not cool the supercharger, it cools the air entering the engine. Superchargers, turbo and any other form of air "compressor" heats the air and an intercooler is an effort to reduce that heat.

 

With ignition on and motor not running you can feel the intercooler fluid moving / pulsating thru the hose(s) when it’s running correctly.

the only effect you’d notice if the pump were inoperative would be diminished performance

Z

 

Interesting, just saw the post above. So that would affect performance huh...
​​​​​​ Thanks, very useful !

 

That makes sense. Didn't think about this.. I'll check
Thanks so much!