...decoding of the vin will show 91 in your case. If you look on the drivers door jam, right under the heading "Nissan Motor Company" will the a sub-heading of Date; that is your Prod Date in MM/YY format, in my case it shows 05/90. My '90 factory service manual (FSM) shows a different vin arrangement than what was posted by ryzan. Unfortunately I do not know how to post a picture, so look in the 10th position of your VIN and you will see an M for a 1991, mine shows an L for 1990. Does this help?