Having gotten used to feel of my plain jane 04 xj8, I was taken aback literally by the snappy feel of a 05 XJ8L a local used car lot let me try overnight. Both cars have the 4.2 and 6 spd trans but the response of the bigger heavier car is quite different. Could somebody have put a high performance chip in it? The transmission is also much twitchier wanting to downshift readily even not in S mode. The average fuel economy from last several hundred miles on the trip odometer is 16.5 while mine on the not L is more like 19. 5 Who knows who has been test driving the L? Anyway, the question for now is can a person readily obtain a high performance alteration of the main ECM that would explain this difference? Or do the big cars come this way on purpose from factory? This is my first drive of one ever. Thank you.

 

Perhaps the trans had fluid changed. How many miles on your car, and how many were on the 2005 loaner? When did you last change the inlet air filter on your car?