Hello all, I have a 2002 XKR with 84,000 miles. It runs quite well, however the supercharger does not seem to perform consistently. I changed the supercharger oil about 2,000 miles ago. Sometimes when you accelerate the boost is obvious. You hear the supercharger whine and it acceleration is incredible. Other times the boost doesn't seem to kick in and it feels like natural aspiration. The boost performance is best with a sharp accretion from a full stop. Is this normal? How do you check the supercharger boost or performance? Ive never had or driven another supercharged car to compare. Thanks in advance for any guidance.

 

Manifold absolute pressure should be available over OBDII. Get a cheap ELM327 and a phone app like TorquePro if you don't have it already.

(disclaimer, XK8 guy here)

Standard diagnostics is to start checking the intercooler pump. It runs with the ignition on and engine off. It is under the air box so you should hear it run. There is a Bosch after-market pump if your failed. This pump circulates water from the intercooler water jackets to a dedicated radiator for the purpose of evacuating the heat generated by compression.

Other thing is to check the XRK flap in the air box. It is supposed to open and allow more air in under acceleration. There is an actuator for that flap that can be checked.

Also, it would be good to record your fuel trims under acceleration for clues.

As usual with perceived performance issues, a number of things can come into play...

Best of luck, keep us posted.