The Vec III is a piggy back electronic unit that allows you to alter several parameters of engine performance. This process does not alter the PCM but does alter engine performance. One of the advantages of the VEC III is that you can have multiple tunes for your engine. A program card enables you to change your tune on the run.
My Vec III reader is in the cab of the truck and it allows me to change my engine performance on the fly. I also have a Valet card which limits the rpm to 2000, and a No Start Card which in effect eliminates the chance that someone can drive the truck away even if they have a key. My normal three program cards are full race, -3 degrees of timing, and -6 degrees of timing.
The Vec III comes with a programming manual and a CD that provides all the info you will ever want to know...
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