The engine bulid code should be on a machined surface on the right side of the block, between cylinders 2 and 3
1st Digit - The year (8 = 1998)
2nd & 3rd Digits - The month (01 - 12)
4th & 5th Digits - The engine type/fuel system/compression ratio (MX = A 4.0 Liter (242 CID) 8.8:1 compression ratio engine with a multi-point fuel injection system)
6th & 7th Digits - The day of engine build (01 - 31)
: Code * 801MX12 * identifies a 4.0 Liter (242 CID) engine with a multi-point fuel injection system, 8.8:1 compression ratio and built on January 12, 1998.