The fuel sync tells the computer when to fire the injector. From my understanding you want to set it as close to 0 as you can for a factory motor. Then depending on mods sometimes the vehicle performs better to have it fire before or after the piston is at its TDC. Its one of those items you set it at zero and try it out, depending on the size of the cam you may want it to be higher on the plus side. Most of the dakota guys with cams try theirs somewhere around +4.