Can this even be done, or is it just for the 4.2 engines and up? I have a 2002 XKR and would love to have a tune along with my exhaust and upper pulley... Even though it's hard to find a place to do it in norcal!

 

For the real world neither the 4.0 or 4.2 can be "tuned". There are chips on the market but they are snake oil! There are some companies that have broken the code on the 4.0 but I'm not sure what they can do. The 4.2 as far as I know has never had the code broken.

 

+1 the ecu's are learning ecu's so remapping supposedly isn't possible. I have read where the codes were broken but haven't seen any info where anything could be done with it.

 

The 4.2 in the 2003-2005 can most certainly be tuned. Look at my XJR for example.

The 4.0 can be tuned, but the ECU needs to be removed from the car and the flash made directly, cannot be done over the OBD2 port.

 

Please elaborate on the XJR "tune"