ok so look at this link explain this to me in lame terms im lost it also states (no obd 2) Apexi-USA - Power FC
"sitting down with a notebook and pencil"
Ok , in lay-mans terms the Apexi Power FC is a stand-alone engine management system meant to totaly replace the oem ecu . Very much like the Hydra Nemesis you lose all OBD2 (on board diagnostic , generation 2) function . They are meant for a pure racecar , with no need to worry about passing emissions inspections or voiding a warranty
A piggyback tuner however only intercepts selected signals to override the oem ecu which otherwise remains in control , so you still have oem driveability and all obd2 functions . The Apexi Neo is a good example of a piggyback fuel tuner .
Apexi-USA - AFC-neo
My Mustang uses a Hypertech handheld programmer that reflashes the oem ecu via the obd2 port . This is the best option which is why i was hoping NGM would eventually go this route with the Forte . It changed the rev limit , top speed , fuel curve , timing curve , shift firmness , shift points etc.