The 'Third Generation' of Honda Preludes refers to the models marked with years 1988 thru 1991.
A Prelude's ECU (along with its attached sensory components) can generally be thought of as the most critical electronic component in the vehicle as it enables the engine to function properly. After all, a car isn't that much fun if you don't get to drive anywhere. Most 3rd generation Preludes equipped with Honda's PGM-FI use an OBD0 ECU identified by the code PK2. The PK2 ECU comes from a family of similar OBD0 Honda ECUs that support Honda engines of a similar period that are also equipped with MPFI (multi-point fuel injection).