just having a google, ive found this page...
http://www.e30tech.com/forum/showthread.php?t=80319
Coding plugs
OBC info: engine type, fuel injection type, tire size,
fuel tank capacity, fuel tank reserve capacity
318i 3-3 TYP 65-81-1-376-027
325e 3-8 TYP 65-81-1-373-698 84-9/86
325e 3-1.4 TYP 65-81-1-381-795 9/86-9/87
325e 3-1.4 TYP 65-81-1-385-941 9/87-
325i 3-1.2 TYP 65-81-1-381-793 up to 9/87
M3 3-1.1 TYP 65-81-1-381-792
528e 5-8 TYP 65-81-1-375-814 85-87
528e 5-1.3 TYP 65-81-1-385-031 88+
535i 5-6 TYP 65-81-1-375-826
M5 6-4 TYP 65-81-1-375-812
635CSi 6-2 TYP 65-81-1-375-021 85-87
M6 6-4 TYP 65-81-1-376-208
735i 7-4 TYP 65-81-1-375-823 85-87
...
Car Model Years Engine BMW Part Number
318 1982 to 9/1985 M10B18 65 81 1 375 816
320 1983 to 9/1987 M20B20 65 81 1 376 032
9/1987 on 65 81 1 385 939
w/ extra fuel tank 65 81 1 376 033 or 65 81 1 381 319
323 1983 to 9/1987 M20B23 65 81 1 376 032
325i 9/1987 on M20B25 65 81 1 385 941
325e 1983 to 09/1986 M20B27 65 81 1 373 698
10/1986 on 65 81 1 381 795
w/ extra fuel tank 65 81 1 381 320
318i/is 1989 to 09/1991 M42 65 81 1 394 111
M3 9/1987 on S14 65 81 1 380 891
what one do i need for a 325i dec 1986 build date / 87 E reg
325i 3-1.2 TYP 65-81-1-381-793 up to 9/87 ?
is there something written on the plug to tell what one you have ?