Over the years, AMC and Chrysler have made many minor and some major changes to the design of the XJ. Here's a rundown, as presented by a Chrysler press release. As I get more time, I'll be expanding this list and adding information that was not generally released.
1984 model year
Initial introduction
2.5-liter OHV four-cylinder engine w/4-speed manual transmission
2.8-liter OHV V-6 engine w/4 & 5-speed manual & 3-speed automatic
transmissions
Part-time four-wheel drive standard, full-time four-wheel drive included
on Wagoneer
1985 model year
2.1-liter four-cylinder turbocharged diesel engine option
Two-wheel drive optional
Limited trim added to Wagoneer
1987 model year
4.0-liter OHV SMPI six-cylinder "Power-Tech Six" replaces 2.8-liter V-6
5-speed manual transmission made standard
2.1-liter four-cylinder turbocharged diesel engine discontinued
1989 model year
Four-wheel anti-lock brakes optional
1991 model year
Upgraded 4.0-liter OHV SMPI six-cylinder engine (190 horsepower, 225 foot-pounds
torque)
1993 model year
Sequential multi-port fuel injection (SMPI) added to 2.5-liter OHV four-cylinder
engine
Models realigned: Base, Sport & Country
1994 model year
Non-CFC R-134a air conditioning refrigerant
Increased roof crush resistance
Side guard door beams for side impact protection
Base model renamed SE
1995 model year
Driver's Side Air Bag
1996 model year
More usable torque & quieter running for 4.0-liter OHV six-cylinder &
2.5-liter OHV four-cylinder engines
Upgraded Selec-Trac® full-time four-wheel drive transfer case
OBD II on-board diagnostics for all powertrains
JTEC Powertrain Control Module
Returnless Fuel Supply System
Okay, so much for the Chrysler hype.
1997 model year
This year was a major redesign of many features. Most noticeably were
the "softer" look where the exterior sheetmetal was given slightly more rounded
corners, the rear fiberglass liftgate was replaced with a metal one, the
dash was redesigned, and great effort went into making the whole vehicle
quieter. There are so many little changes that the 97+ years really
warrant their own page. I'll be getting to this soon.