catback system

dodgent i have a 96 dodge ram 1500 with the catback system i want to turn it into true duel myself. Instead of buying another cat i just want to keep the stock one in the same spot and take the pipe from the right manafold and run it straight pipe. Im not sure if the catalitic converter measures how much exhaust is going through it so i dont know if this will turn my check engine light on or do some thing to my motor like run it too rich or not rich enough i have a o2 sensor after and in my cat