• Jeep often used engines by the American Motors Corporation, which was ultimately bought out by Chrysler in 1987. With a variety of four-, six- and eight-cylinder engines available to different Jeep models, the 4.2 liter inline six cylinder AMC engine was an optional engine for Wranglers between 1987 and 1990. Before 1987, the 4.2 liter was offered in the CJ series Jeep trucks. Jeep CJs were precursors to the Wrangler, with similar body styling and engine options to both.
  
  

Performance

• The AMC 258 cubic-inch motor that was featured in Jeep Wranglers from 1987 through 1990 had less horsepower than the four cylinder, 150-cubic inch engine that came standard in all models. With only 112 horsepower, the inline six cylinder engine put out an impressive 210 ft/lbs of torque, which was much higher than the four cylinder's 135 ft/lbs of torque. Considering the Jeep Wrangler YJ's main focus was in off-road mobility, consumers saw the torque advantage of the six cylinder to be a deciding factor. With a stroke of 3.895 inches and bored cylinders at 3.75 inches, the 4.2-liter engine available in the Wranglers was close in fuel efficiency to the smaller, four cylinder engines available as a base motor. Jeep advertised this AMC engine at 18 mpg city and 25 mpg highway.
  
  

Drivetrain

• One of the strongest and most used manual transmissions, the Aisin-Warner AX15, also used from 1987-1990 in the Wrangler YJ. The gear ratios in manual transmission Wranglers varied between 3.07:1, 3:54:1 or 3.73:1. A powerful and capable five-speed transmission, the AX15 was paired with the New Process NP231 transfer case from 1988 to 1990. Previously, the 1987 model Wrangler YJs came from the factory with the NP207 transfer case. The later model NP231 transfer case had a higher ratio at 2.72:1, giving it a bit more power during gear shifting. The TF999 was a three-speed automatic transmission for consumers who opted for this luxury, which was manufactured by the Chrysler Group. The gear ratio available to automatic transmission-equipped Wranglers with the 4.2L engine was 3.54:1. The same transfer cases were paired with this transmission through each year, respectively.
  
  

Axles and Suspension

• Front and rear axles were manufactured by the Dana Holding Corporation. The front axle was a reverse cut Dana 30, similar to previous versions of the Dana 30 axles featured in light-duty Jeeps. The rear axle of the 4.2 Jeep Wranglers was a Dana 35c, using 10-inch drums for stopping capabilities. With 40-inch spring pads, the YJ was ready for off-road use with its durable axle and suspension combination.