ECU messing with MPG?

I have a '93 Classic with JDM 10:1 motor in it and a California ECU. The car is not a California car but I fried my ECU a while ago and had to buy a new ECU so that's how I ended up with a Cali-ECU in my car. Will this effect my gas mileage? The only thing different between the two ECU's is that the Cali one is looking for an exhaust gas temp sensor which my car doesn't have. Because I don't have this sensor I get a CEL. Is the ECU dumping more fuel in the engine because there's no reading from the sensor so it dumps fuel in to be safe? Any ideas? Thanks.