What are the differences between Federal cars and California (CA) cars?

CA cars have more stringent emissions requirements than Federal cars, so they have a couple of extra pieces of equipment. An exhaust gas recirculation (EGR) solenoid valve is installed on CA cars next to the fuel pressure solenoid valve, while Federal cars have a empty space there. 1G CA ECUs are programmed slightly differently than Federal ECUs, making it problematic to switch ECUs from car to car without getting error codes.

To add to the confusion, all 1994 USA DSMs had California emissions, meaning there are technically no Federal 1994 cars. This prevents 1994 owners from installing an EGR blockoff plate, as the CA-style ECU is smart enough to notice and flag an error code. This requires the substitution of a 92-93 Federal ECU for the original CA ECU.

[Other changes to be added.]

Other than that, there are no differences between Federal and CA cars.