Either "Engine Management Advanced Tuning" or "Designing & Tuning High Performance Fuel Injection Systems" both by Greg Banish is worth reading. It will give you a sense of respect for all the conditions which the EFI parameters and tables have to control. Aftermarket tuners when they modify these don't understand everything that happens while driving on the street and screw it up, sll they do is modify for max power on an inertial dynomometer which is not real world conditions. To my knowledge the algorithms in an engine computer are proprietary and protected. Tuners do not modify this part of the computer, instead they only modify numbers/parameters which have been set by the manufacturer that the algorithms use to make the engine run optimally. Without having access to the actual programming code to figure out the far reaching affects resulting from changing the values that they do, or having instructions published by the source (i.e. manufacturer), tuners are guessing and assuming. And in doing what they are doing is technically saying they know better than the manufacturer... on modifying something there is no way they can have complete knowledge of. I am unaware of any car automaker publishing any kind of instruction how to modify an engine computer. Furthermore i'm pretty sure it is against federal law to modify an engine computer because of emissions laws- that is for a registered vehicle driven on public roads. Like most things automotive aftermarket it is a scam. 2 basic examples of how tuning can be scam, a tuner can sell you on a tune and it actually feels like your vehicle has more power or get up and go, when all they really did was remove the torque management feature where in an electronic gas pedal type vehicle you can mash pedal instantly to floor the throttle blade does not open as fast; there are parameters which govern the rate which the throttle body opens to protect the vehicle; my 8.1L with allison along with many other trucks has this tq mgmt feature for a reason to prevent drive train failure. And you can also observe this in rental cars where mash the pedal and the car takes off like grandma driving. By making the throttle blade open faster in relation to how much you push the gas pedal down deceives the driver that the vehicle has more power. the most common is making max wide open throttle horsepower by leaning out the A/F tables from the oem 11.5 to 12.5 range up to 13.0. That's what everyone does when they buy EFIlive or HPtuners. This does increase max hp if done right, but it was not done by the auto maker because the resulting high exhaust heat then reduces the life and kills the catalytic converters. there are a few ways to achieve this leaning of the A/F tables and what happens is it'll work for the narrow operating condition of 1/4 mile pedal always on floor, but it can and usually does screw up many other things that make the vehicle run well on the street under varying loads. Does a tuner tell you exactly what he/she changed? Any do they offer a means to go back to the oem / original settings in a way you are sure they are not lying or deceiving you? If not then what does that say about your tuner?