Hello all,
I have a question and any help is greatly appreciated. I have a 2000 XKR convertible with 50K on the odometer. I have recently replaced all cam chains,tensioners and any associated parts along with that job.
The car starts fine, runs well, idles smoothly and still gets up to 110 mph with no qualms. Last week, I was idling in the garage and revved the engine to 3K on the tach, the engine started to roll from 2500 to 3000 rpm. Not a real chug or violent roll, but a consistent back and forth in 3-4 sec intervals. It also did not want to rev above the 3K mark. Now, take the car out on the road and punch the throttle, it revs past the 3k upto 4K without hesitation and not a buck or hiccup.
So under a load, it seems to be good, just without a load on the engine does this rolling thing happen. Any suggestions as to what it might be? Is there a relief valve for the supercharger in the system? maybe fuel related? This is my first Jag and this forum knows everything, so I'm hoping for some direction...
thank you

 

Air leak after MAF (Mass air flow sensor) near the air filter ..probably the clip not seated or tightened right.

 

Your 4.0 XKR engine should not rev past 3,000 rpm when in park. That is normal and controlled by computer.

Z

 

Well that would explain it. thanks Z also thank you psitnbroke. I will check the intake for anything loose. Always a pleasure to have info through experienced owners.

 

If you don’t have a complete set of owner manuals I believe they are available for download here on the forum. The manuals can answer many questions and will help to acquaint you with the cars many idiosyncrasies.

not sure if the 3,000 rpm limit is mentioned in the manual but it might be.


Z

 

Rev limit at 3000 & cuts out to do that.

 

My guess is that the rev limiter is involved in this. It sounds like it is bouncing off the limiter. Since it is a part of the ECU management, you will need to take it to a shop and have it scanned. You mentioned he supercharger, and yes, there is a bypass valve, and it is vacuum operated but I doubt that this is your problem. The bypass is designed to bypass the supercharger when the engine doesn't need it, eg. at low rpm or idle. The bypass operates by opening up at high vacuum and letting the engine run normally aspirated. When the vacuum drops, it closes and puts the supercharger on pressure for performance. This function increases gas mileage and cuts wear on the parts some. If the vacuum motor is leaking, it might cause some speed fluctuations, but you would also not have normal performance. Probably the rev limiter getting a bad signal.

 

As above. The engine management will inhibit rpm above ~3000 while the car is in park or neutral.

 

The reason the engine is limited to 3,000 rpm with no load is to reduce stress on internal engine parts such as the connecting rods. Avoid revving the engine when it's not under load.

 

^^^^^^ +1

this applies to all engines, especially high performance engines.

Z

 

and especially before it reaches operating temperature !