I have a '03 XJR. The up-shifts are very soft, even in sport mode. I think the computer actually cuts the power momentarily during up-shifts. Is there an inexpensive way to make the trans. shift harder?

 

Yeah, drain about 1/2 the transmission fluid.....

:-P

Seriously, no. You'd have to modify the TCU, and the way it interfaces with the ECU. Unfortunately, tuning Jag's isn't exactly common, so very few companies offer products, and the ones that do don't have much available.

 

I don't know this trans, but on any other computer-controlled auto, the best mods to firm up the shift are in the valve body instead of the controller. How about these guys? We are talking about a W5A580, so it's got to be very similar.

http://www.importperformancetrans.com/722.6.shtml

 

its funny you mention them brandon since i just got my valve body back from them to increase line pressure and shifts speed on the frontier. Now that i supercharged it my 1-2 shift spans 600rpm. Unfortunatly they "lost" a part of the electronics for the valve body i had separated in the box with a seprate bag that went in the trash. Now intead of reinstalling after work tonight im waiting for them to get another from the dealer and have it shipped..so yes call them and find out and i was actually gonna call them about this too. You can also have transmission adaptation cleared and then when taking it back instead of driving easy and no sport mode, drive it hard in sport. Havent done this but that may make thetrans relearn harder shifting.
Their #866 828 7267 talk to ty
i BREIEFLY TALKED TO TY AND HE SAID THEY CAN DO EVERYTHING FROM INCREASE THE STALL SPEED, TO MOD THE VALVE BODY, TO DO THE FULL HI PO TRANS BUILD

 

Try tractioncontrol and sport mode off. I have noticed that the traction control kicks in all the time, sometimes the asc light comes on sometimes it doesnt. With traction control off in my 03 its like a whole different animal. Could be why the upshifts are lacking I have noticed mine does it too, never really noticed whether it is with or without the traction on but just in general.

 

Did you mean sport on? The traction control is always off, totally worthless, especially in the snow.

 

Sport mode raises part throttle shifts up a couple 100 rpm, and when you punch it on the freeway, instead up downshifting 1 gear, it goes 2 for much better acceleration. I tell people to leave sport on all the time, since you really wont notice under normal driving, but if you inadvertantly pull out in front of a semi on the road, youll be glad it downshift to gears to get you the hell out of the way faster...and traction control is always on , you have to turn it "off" light on after each key cycle to keep it from interviening....that being said, it still does just not noticebly, this is why i put a relay into the power circuit of the abs module on my frontier"aka burnout mod" cause even with traction off and a fry by wyre throttle body, it still intervenes.