A year or so ago, prior to getting interested in self tuning I purchased a Hypertech tuning module (pigtail) attached to my PCM (1994 Z28 has flash , not chip). This may be a silly question, but how does this module actually work. I can read the PCM using TunerCat with and w/o the Hypertech installed and the tables are the same. I always disconnect it prior to writing to flash to alter fan, speedo or shift points. I will eventually have to take it off completely as I get into timing and fuel ration changes. However I am very curious on how this thing actually works, does it use the same table information but alter how the PCM manages timing and fuel ratios with variables or tables I can't see ??

 

all the piggyback module does is fake out your maf/iat sensor readings and maybe some other sensors, it does nothing to the actuall tune in your pcm