See Figure 1
The engine serial number for the American Motors-built 2.5 Liter engine is located on a machined pad at the rear right side of the block, between the No. 3 and No. 4 cylinders.
The digits of the code identify:
- 1st digit-The year (3 = 1993).
- 2nd and 3rd digits-The month (01-12).
- 4th and 5th digits-The engine type/fuel system/compression ratio (HX = a 2.5 liter [150 CID] 9.1:1 compression ratio engine with a multi-point fuel injection system).
- 6th and 7th digits-The day of engine build (01-31).
For example: Engine code 301HX23 identifies a 2.5 liter (150 CID) engine with a multi-port fuel injection system, 9.1:1 compression ratio and built on January 23, 1993.
Also on the block, just above the oil filter boss (near the distributor), is the oversized/undersized component code. The codes are explained as follows:
4.0L AND 4.2L ENGINES
See Figures 2 and 3
The engine code is found in the identification plate on the firewall. The second location is on a machined surface of the block between number 2 and 3 spark plugs. For further identification, the displacement is cast into the side of the block. The letter in the code identifies the engine by displacement (cu. in.), carburetor type and compression ratio.
All of the engines have the same undersize/oversize letter codes, located on the boss directly above the oil filter (near the distributor. The parts size code is as follows: