Yes, completely separate tune. A FICM
tune modifies the programming in the FICM
, whereas the other tunes modify the PCM
Exactly how it does it is a closely guarded secret. If everyone knew exactly how it was done, companies all over would be duplicating the process. However, basically what they do is change the timing of the injections, the length of the injections, and the number of injections per stroke. Here is an exaggeration of one possible change....
In an old engine you might get 1 injection per stroke. The injection occurred 45 degrees BTDC, lasted 36ns, and it injected 2CCs of fuel. (please remember, I'm making this crap up...I have no idea what real figures would be, but I do have the general concept down) With this process you have too much fuel in the cylinder at one time which results in unburnt fuel washing down your cylinder walls and coming out of your exhaust, and/or partially burnt fuel pouring out the exhaust as black smoke. Everything runs, but it's rough as hell and there's not a lot of power. Modern engines have changed things to give two or three injections per stroke. It starts with a little one somewhere around the same point as stock, lasts only 10 ns, and injects 2/3CC. The second is somewhere around the point of ignition. The third is after ignition, but still during the flame-front phase. The same amount of fuel gets injected, the injection duration is a little less with different timing, but nearly all of it gets consumed resulting in less waste, more power, and better MPG
This is the same concept with the FICM
tuners, but they have added more injection cycles and tweaked the timing. You inject less fuel more often, at more appropriate times, and get an increase in power, reduction in fuel used, and a smoother running engine.