WHAT IS THE DIFFERENCE BETWEEN A "CALIFORNIA EMISSIONS" AND A "FEDERAL EMISSIONS"

4.0L IN A ? The engine in my jeep has been replaced. I think it originally had a federal engine because it had only 2 O2 sensors. Now it has 2 by the converter and 2 pigtails on the back of the engine. I keep getting a bad O2 sensor code and occasionally it will stumble on acceleration and has no power. I have replaced the fuel filter and show good fuel pressure. This is driving me nuts because I can't depend on the motor not running rough. This is only an intermediate problem. What do I need to do???