Is a 93 new enough to even HAVE a knock sensor?
If the 300ZX is the non turbo version, then you might get away with it, but check the owner’s manual to be sure. If you just bought this car and it doesn’t have one, check some place like ebay or http://www.books4cars.com/ and get one.
I was nice enough to find it for you:
http://www.books4cars.com/result4.asp?findtype=Owner&imageField2.x=21&imageField2.y=16