The first letter is the engine series (F, H, J). The next two numbers are the displacement and the final two are the engine revision. F and H are four cylinder and J is six cylinder.

Pop your hood and look for a white sticker with black computer generated letters. That sticker should have the entire series of numbers you are looking for. On my 98 V6 it's on the passengers side by the alternator and shows the J30A1 code.