The Jeep 4.0 liter sixcylinder engine provided exciting acceleration in Jeep Wranglers for years, with excellent torque. Based on the old 199 cubic inch Typhoon Six introduced in 1964 (via the talldeck 232), the AMCengineered engine used a shallowskirt castiron block with evenly spaced cylinder bores, loopflow combustion chambers, inline valves, and a sevenmainbearing crankshaft. According to AMC historian Frank Swygert, the 4.0 block is around 1/8" wider, due to the 0.10" larger bore, and the lack of mechanical fuel pump support; 4.0 heads can be bolted to the earlier 232 and 258 I6 blocks (the ports on the right edge have to be sealed when this is done, to avoid seeping coolant).

To create the 4.0, the older engines' bore and stroke were also changed, but engineers tried to preserve parts and dimensions to reduce the need for new tooling and inventory; all internal parts interchange, according to Swygert, among the late1964 and newer sixes in the 232/258/4.0 family. He wrote that it's "relatively common to put a 258 crank and rods in a 4.0L to make a 280 inch six. This can be done with all stock parts (258 crank/rods, 4.0L block/pistons), but most often a special piston is used along with the slightly longer 4.0L rods.

When the 4.0 first came out, AMC was using two six cylinder engines, a troublesome 2.8 liter V6 from General Motors (with a similarly troublesome Ford carburetor) and AMC's 258 CID (4.2 liter) straightsix, which had been derived from the 232 cubic inch six. The 4.2 was used in the CJ7, Concord, Spirit, and Eagle, after having debuted as the sole Eagle engine and an optional Wrangler motor.

A related engine, the 2.5 liter fourcylinder, was based on the same basic architecture, and appeared in 1983; Frank Swygert wrote that it was essentially the 258 with the center two cylinders removed and a new head. The 2.5 was engineered by AMC to be "part of a twoengine set," according to Willem Weertman; the other engine would be the 4.0 liter six. The fourcylinder produced 125 horsepower in its final years, and replaced a 2.5 liter GM engine; to confuse matters, Chrysler made a 2.5 liter four as well, producing a meager 100 hp with throttlebody fuel injection.

The YJ gave way to the TJ for the 1997 model year (note that there was no 1996 model year; the 1997 TJ was released in Spring 1996). This updated Wrangler featured a coilspring suspension (based on that of the Jeep Grand Cherokee) for better ride and handling, and a return to the classic CJ's round headlamps. The engine is the same 4.0 L AMC 242 Straight6 used in the Cherokee and Grand Cherokee. A 2.5 L AMC 150 Inline4 motor was available on entrylevel models until 2003 when the 2.4 L DOHC 4cylinder engine previously used on the Chrysler PT Cruiser replaced it.
A right hand drive version of the TJ was available for export markets, and was also offered for sale to US rural route postal carriers. The version offered to US postal carriers was only available with an automatic transmission.


A modified 98 TJ offroading in Alaska
In 1999, the fuel tank became standard at 19 U.S. gallons (72 L; 16 imp gal) capacity. There were some changes that occurred between the 2002 and 2003 years that made some parts difficult to directly swap back and forth, but also made it easy to identify certain years. From 1997 to 2002, the side door mirrors were black metal framed mirrors; and from 2003 to 2006 they were plastic molded mirrors. The fit of hard and soft tops is slightly different, and the fabric and colors available changed from 2002 to 2003. In 2003, the 3speed automatic transmission was replaced with a 4speed automatic with overdrive. It has the standard option of turning off overdrive with a dash switch if desired. The radio bezels went from a rectangle in 2002 to a rounded edged rectangle in 2003, so swapping these also required the console to either be swapped out or modified. The sound bar inside was changed to sound pods. The interior seats also changed design from 2002 to 2003, going from a rounder model to one with a distinct separation between back and headrest areas.
The standard skid plate was also revised for 2003 to make room for the Rubicon's bigger NV241OR transfer case. The change from the 30/32RH to the 42RLE also gained an additional skid plate.
This version of the Wrangler is also notable for being the last production vehicle to use AMCrelated parts. The AMC Straight4 engine was retired after the 2002 model year, and both the AMC Straight6 engine and the door handles (the latter of which first appeared on AMC vehicles in the late 1960s) were retired along with this generation in 2006. Like the YJ Wrangler, the TJ Wrangler used both the AMC passenger car door handles as well as the larger door handles off the AMCbuilt Jeep CJ for higherend models.