Ok, I’m open to the concept you know more about this.
Prove it.
It's impossible to quickly prove something to someone who doesn't even understand the basic concepts of the subject. Just take some time and do some research on ECU spoofing by altering the sensor inputs. It is really a very basic concept. I will say this much below and maybe you can take it from here and go in the right direction.
The whole point of any piggyback is to modify the input information to the ECU so it will perform the normal programmed routines without ever knowing it has been spoofed. It does NOT have the capability to alter the ECU code/programming at all. It IS possible for the piggyback tune to alter the sensor input to the point that the ECU triggers a fault or otherwise does not play well with the ECU programming. This happens when the tuner tries too hard to reach into the deeper levels of the ECU in a desperate attempt to compete with flash tuning at the ECU programming level.
Piggybacks are a very top-level tuning device only able to affect basic inputs like the timing, manifold pressure, and on older port-only injection engines, the injector pulse-width for AFR control. Newer direct injected engines have such a short window for injection that a piggyback just isn't fast enough to alter the pulse-wide effectively for "reliable" control. This is one reason why they aren't as effective on the latest electronic engine controls designs.
They (piggybacks) had their vital place in the evolution of aftermarket tuning, but were wholly bypassed about a decade ago. Those folks still trying to market them are a dying entity because they can't compete at current levels of engine control technology.
This still doesn't dispel the fact that they can't be detected UNLESS the tuner tries too hard and sets a fault in the ECU, which is a recorded event. I would expect the tuner to set many faults in their initial dyno quest to create workable tuning parameters as they learn the ECU.
A tuner using a piggyback, but having access and knowledge of the ECU code can come up with an effective tune file for simply "more power", but unless they alter the actual Load/Torque/Throttle lookup tables (and there are many) within the ECU, they're limited in how much additional power they can safely and reliably extract from the engine/ECU combo.
Hope this gets you started on the way to enlightenment so that ECU tuning is not some black art, but a systematic, well-defined process. If all else fails, just try a google search and start on reading the technical papers, not forum posts.
