The "programers" are only made for OBD II ('96 and up) equipped vehicles. The reason why is because the OBD I (your '91) system is unidirectional (it will only send info to the ALDL, it can not recieve it). Part of the government mandations that mapped out how the OBD II system was to work, was to make it bidirectional. Therefore you can send and recieve information through the ALDL. The "performance" chips available for the OBD I alter the pramaters outside of the computer, were as the "power programers" alter the actual programing of the computer.
