The stock MAP sensor is left on the firewall and a wire from the fuel/timing calibrator is tapped into it to feed a MAP signal to the stock computer. The stock MAP sensor is a 1-bar sensor, which means it can only read vacuum. A 2-bar sensor is needed to read boost, but the stock computer isn't set up for those readings. So, a vacuum line is run to the Split Second calibrator, the 2-bar sensor in the unit analyzes manifold pressure and then feeds the stock Jeep computer a reading it can use. In this manner, the Jeep computer still runs the engine using the stock O2 and other sensors.