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The AMC 2.5 liter four-cylinder engine


Not to be confused with the Chrysler 2.5 liter engine.

by Robert Clark

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The 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.

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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 Stroke3.88" x 3.19"
Displacement150.4 ci 2.5L
Main Bearings5
Valve ConfigurationOverhead valve (8 valves), flat followers, hydraulic lifters (1997)
ConstructionCast iron block and head
Redline5,600 rpm
Gas needed Regular (87 octane)

Generations



Jeep 2.5 engine

1996-20021991-1995
Wrangler
1991-1995
All But Wrangler
1987*-1990 1982-1986*
Compression Ratio9.2:19.1:19.2:19.2:19.2:1
Horsepower120-125 @ 5,200 rpm [email protected] RPM130 @ 5,250 117 @ 5000 RPM105 @ 5000 RPM
Torque140-150 @ 3,250 [email protected] RPM149 @ 3,250 135 @ 3500 RPM132 @ 2800 RPM
Fuel Delivery MethodSequential InjectionMulti Point InjectionMulti Point InjectionThrottle Body Injection1 Barrel Carburetor

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

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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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