4.0L Engine Date Codes

Engine code location

The date code is on the passenger side of the engine, on the block, just forward and up from the distributor on a machined flat surface.

The digits of the code identify:

  • 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) 8.7:1 compression ratio engine with a multi-point fuel injection system).
  • 6th & 7th Digits-The day of engine build (01 – 31).

FOR EXAMPLE: Code * 801MX12 * identifies a 4.0 Liter (242 CID) engine with a multi-point fuel injection system and 8.7:1 compression ratio that was built on January 12, 1998.

Revised 1-31-2016

2 thoughts on “4.0L Engine Date Codes”

  1. Cruiser,

    Just wanted to thank you for all your work on this site. I have a 87 Cherokee and I’m currently going down your list as we speak. Your a jewel of knowledge sir!

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