how does the harness device work in regards to the pcm for changing power output ( i.e. fuel ) - i know that they will do it by timing, pulse, rate, etc, but does the harness actually take the information being put out by the pcm and alter it or alter the pcm directly ?

tom - a signal comes into the box, and gets modified on its way out.. PCM doesn't know its there...

thats kind of what i thought but wanted to be sure as i wasnt sure if it actually altered the figures in the pcm directly or altered the signal as it passed thru. makes sense, thanks

so when stacking, im assuming that the harness device looks at the figure coming thru and alters it a given amount to get the extra power that it is programmed for ? or is it just a set parameter and if the pcm is already putting out enough, the harness device wont add anything to that figure coming through it ? Did that make sense ?? does anyone have info on this, trying to put it all together for some future tests

I am curious about the "fingerprint" that is left by programmers, I have an "Edge" and after reading this post I believe that there is no trace that the dealer could find of its use, am I correct?

eddie - you are correct, although some people from time to time come up with this crap about " well gm said they can do bllaaaaaah blaaaaah blaaaah " stuff, but im pretty sure thats just gm people trying to keep people honest and thinking about it, nothing more, and that goes for a harness device like edge or a programmer

back to the question in regards to how the harness device alters the signal. what im trying to figure out is if will perhaps take away if it sees a number that is already greater than what it is looking for. how are these things programmed, what do they look for, and what is the end result of that signal it receives ? does anyone know ?