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The AMC 2.5 liter four-cylinder engine

Not to be confused with the Chrysler 2.5 liter engine.

2.5 liter AMC - Jeep engineThe Jeep 150 cubic inch four-cylinder engine was introduced by AMC in 1982, for the 1983 model year.  The engine used a carburetor until given throttle-body fuel injection in 1986 (except in the Wrangler, which switched in 1987); in 1991 it switched to multiple-port fuel injection, and in 1993 moved to sequential multiple-port fuel injection.  The major change over the years has been the different fuel delivery methods, though minor changes and refinements were made as well. 

The I4 uses overhead valves with hydraulic lifters and a cast iron head and block.  It is said to be a 258 ci AMC straight-six with two cylinders lopped off, bored to 3.88”, and de-stroked to 3.19”.  The head’s chamber and port design were later used with the perennial favorite Jeep engine, the 4.0L Straight-6

While clearly superior in power to the Plymouth-Dodge 2.5 liter engine, which produced at most 100 hp and 135 lb-ft of torque, the AMC engine co-existed with its corporate sibling; it did not even make it into the Dodge Dakota until 1996, when it replaced the 2.5 liter four-cylinder (a stroked 2.2 liter engine) which was no longer cost-effective to manufacture, since the cars that used it had been discontinued. The 2.5 would eventually be replaced by the corporate 2.4 liter engine (producing only a little more power). The Dakota dropped its four-cylinder option entirely.

W. Paul Tippett, president of AMC, was quoted by the New York Times as saying that it had made sense to buy four-cylinder engines from GM at first, because demand was low, but with the public using more of the engines, it made more sense to develop and build their own. The popularity of GM’s new four-cylinder cars may well have made supplies questionable as well.

amc engines

While some believe there were no cars made with this engine, a very small number of early Eagle Premiers - modified Renault Medallions - were built with the 2.5 in 1988 and possibly 1989. However, most found their way into the CJ7/Wrangler, AMC Eagle, Cherokee, Comanche, and Dakota.

In 1997, the Dakota’s 2.5 liter adopted a "quarter-wave" tuning chamber in the intake duct and a Helmholtz resonator mounted atop the throttle body to reduce induction noise and provide a pleasant sound. (Click for details.)

The 2.5, as used by AMC, used a General Motors bellhousing pattern, instead of the AMC bolt pattern, because it was a replacement for the Pontiac “Iron Duke” four-cylinder purchased by AMC while they adapted their straight-six into a four-cylinder.

Specifications

Bore x Stroke 3.88” x 3.19”
Displacement 150.4 ci 2.5L
Main Bearings 5
Valve Configuration Overhead valve (8 valves), flat followers, hydraulic lifters (1997)
Construction Cast iron block and head
Redline 5,600 rpm
Gas needed Regular (87 octane)

Generations

Jeep 2.5 engine

1996-2002 1991-1995
Wrangler
1991-1995
All But Wrangler
1987*-1990 1982-1986*
Compression Ratio 9.2:1 9.1:1 9.2:1 9.2:1 9.2:1
Horsepower 120-125 @ 5,200 rpm 123@5250 RPM 130 @ 5,250 117 @ 5000 RPM 105 @ 5000 RPM
Torque 140-150 @ 3,250 139@3250 RPM 149 @ 3,250 135 @ 3500 RPM 132 @ 2800 RPM
Fuel Delivery Method Sequential Injection Multi Point Injection Multi Point Injection Throttle Body Injection 1 Barrel Carburetor

* The Cherokee and Comanche gained fuel injection in 1986, bringing it to 117 hp.

2.5 liter engine power

In 1997, the engine was noted as having flat followers and hydraulic lifters. The redline came at 5,550 rpm. Fuel was standard 87-octane unleaded. Oil capacity was 4.0 quarts, coolant 9.0 quarts; emission controls included three-way catalyst and dual heated oxygen sensors. Gas mileage in the Wrangler was 19/21 manual, 17/19 automatic.

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