Do the 98s have the mpg display in the cluster? Maybe I'm losing it, but I distinctly remember my 03 XJR having that (and it being very low ). Either the 98s don't have it or I can't figure out how to display it? Not many buttons there, not sure what I'm missing.

 

You should be about to scroll thru the info from the left hand stalk (lights) button.
instant fuel
average fuel
trip
mileage

 

That's it! Thank you Sean, been a while since I had the 03 and completely forgot about that. I was trying every combo of the buttons on the RH side of the dash (Clear, 000, A/B) and nothing was working. Couldn't for the life of me remember how to get through the menu. I'll give it a shot later, thanks again.