o2 sensor

i have a 88 4x4 xj with auto tranny and a 95 4.0 installed with my stock electronics it's runnin a little rich is my o2 bad?

How do you know it is running rich? Did you use an exhaust gas annalizer to get the reading? It could be your O2 sensor but running too low a thermostat will also stop it coming out of open loop into closed loop where it uses the O2 sensor to run at 14.7. A.F.