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I have a 1998 C5 Hypertech Prgrammer and I've lately installed some new taller tires. I know it can change the tires for me but what I am wondering is will it keep the custom tune I have installed? I've never married the programer to my car since I bought it a few years ago so it doesn't know what I have for a tune. Will it copy the tune I have into the programmer and think that's the stock one for this car? I don't need to have the tune done over again and spend another $4-500 to fix it if it throws a generic GM tune into the car when I'm done.
I went ahead and adjusted my speedo from the programmer. I'm 99% sure when it writes the new program into the car's computer that it downloads what tune I have in the car to the programmer before it's writes the new parameters I typed into it. Hope that's the case anyway.
I used SCT and tuned Fords so I can only speak in generic terms.
It's been a while for me but as I recall yes the cars stock tune is first flashed onto the programmer (flash device) then what ever tune the tuner put on it is flashed to your cars computer.
Within that tune they give you ability to change things to a small amount. Like timing, fuel, tires, ect...
btw, don't sweat the small amount of changes to timing and fuel that it gives you ability to change. A professional tuner will have it dialed in as delivered. (they generally tune for power then add 2-3% of for margin)