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Best is to look at the block and head casting numbers.




Year...........Casting No.

1987-90......53005535 (8933002665)







Year...........Casting No.





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From the I-6 FSM:


Build Date Code


The engine Build Date Code is located on a machined surface on the right side of the cylinder block between the No. 2 and No. 3 cylinders.


The numbers of the code identify the year, month and day that the engine was built.


1st character (year): 6 = 1986 | 7 = 1987 (presumeably 8 = 1988, etc)


2nd & 3rd characters (month): 01 - 12


4th character (engine type): M = 4.0L


5th & 6th characters (day): 01 - 31


My FSM only covers thru 1987 on the engine, but I think it's safe to assume that 8 means 1988 and 9 means 1989. I would read your code number ... 903mx17 ... as 4.0L built March 17, 1989.


I don't have a clue what the 'X' means. The FSM makes reference to an additional code 'E' or 'W' for vehicles sold in Georgia or Tennessee, but these codes include numbers and are not IN the engine date code (example: E-1197277)

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