I've had my XF for almost a month now, and I love it.
One thing that puzzles me is that when I'm getting on the throttle a bit, that at around 6000 RPMs, it seems that the fuel cuts off. The car does not stall, it just loses all it's power. When the RPMs drop down after shifting up to the next gear, it resumes normally. Is this normal? I guess it could be an RPM limiter, I'm just not sure.
BTW. Mine is a 2004 ltd with the 6 speed.

 

I think you hit it on the head about the rev limiter, its happened to me several times. I believe the limiter is set around 6200 or 6300, but don't quote me on that, I'm not sure exactly what happens, if it cuts the fuel or what, but when you hit the limiter you lose power til you shift gears. Hope that helps, somebody else can probably explain it better.

 

It probably cuts spark not fuel. If it cut fuel it would make it lean, and lean is bad, very bad.

 

if it was lean, the dam motor would blow.

 

I haven't been able to find the exact reference, but it most likely cuts all fuel to the engine. If it cut the spark, but continued to feed fuel into the mix, it would be pumping the raw fuel air mixture out the exhaust, which would be VERY BAD.

When I worked at 3M during the early 70's, we were developing an aftermarket/oem converter. One of the tests we did was to hook up an engine to a large mass (a 60 hp motor), run it till it was hot and kill the ignition but not the fuel supply. Suddenly getting raw fuel/air mix the catalyst tried to burn off all that unburned hydrocarbon. The test melted the exhaust pipe and part of the converter. If this had happen in a car, the heat would have easily burned a hole in the floor and probably would have set the car on fire.

This behavior was one of the driving forces to go with all-electronic ignition and to add electronic shut-offs to the carbs (and finally replace them with fuel injection).

 

As the throttle is controlled by the chip (plus pedal sensor) and not directly by the acceleration pedal, I think the wide open throttle is being closed to limit the rpm. Like you would release the pedal.

I hope you understand what I'm trying to say.