Most ECU (Electronic Control Modules ) and in our case the PCM (Powertrain Control Module) use a common way of regulating the air/fuel and timing that the engine will use. Now please understand this is a simplified explanation as many other things happen in closed and open loop processes. The PCM contains a map (you can sort of look at this as a multi dimensional spread sheet) that has the parameters set that control the air fuel and timing for every 1000 rpm (this varies by builder). The PCM reads this data combines it with other behavior and generally sets the fuel injectors fuel delivery, the time they deliver fuel and how long. It also sets the ignition timing to match this fuel delivery. Other information that regulates the map is the amount of available air to charge the cylinder . There are other memory locations that have memory locations for rpm, tire diameter etc.OK so I know I'm showing my ignorance but hey gotta ask questions to learn right?
What do these "tuners" actually do?
My limited understanding is that they allow vehicles to run at higher octane fuels? correct or am I way off?
I know they alter the vehicles electronics so I would assume they are a warranty voider.
By reverse software engineering Diablosport with the Predator gives you three different air/fuel/timing maps that increase the performance of the car. If timing is advanced you need higher octane gas to prevent detonation, so they simply matched their "tunes" with octane ratings.
The Predator, however, is far more flexible. Diablosport sells a software package called CMR that allows a "tuner" to put your car on a dyno and dynamically alter the mapping of many different parameters and they can then be flashed in the Predator prom. For example, my supercharger installation needed a custom tune to get the proper air/fuel timing as I was supplying a lot more air, so you can get in a lot more gas, but you need to be careful not to advance the timing, it may be retarded, so you don't get detonation, which will really wipe out the pistons.
There are also transmission control units that exchange data with the PCM.
With our 42RLE 4 speed Neither the Predator nor the CMR software will give you access to these parameters, however some control was given over the NAG1 in 2009.
As I said, this is a simplification, but it should give you the notion of what the Predator does. It does not change the electronics, it changes the data the control electronics reads. I hope this helps a bit.