ok so i swapped out my california emissions motor 4 cyl in my 99 for a normal us motor but am getting horible gass milage probably 4-10mpg now i was wonerding if this coul dbe cause by the differnt injectors in the two motor and me not switching the ecu. so if i switch my ecu to a normal one and not the cali one wil it fix my problem?

 

The California engine has at least different exhaust oxygen sensors, cylinder head (and injectors), catalytic converter. If the replacement engine was from a manual trans car it may have a different EGR valve.

The two engines should get about the same MPG.

Each computer is specific to the year, emissions, trans type. Find the correct computer.

 

so a year later and i still havnt fixed it,. this is where i am currently standing. usda motor and tranny cali spec car, usda ecu, usda fuel air ratio sensor, cali spec oxygen sensor, cali spec wiring and all other emission garbage,... some one please tell me what i need to do to get better mpg and my check engine light off,. its throwing p0125 and p0135

 

Make sure the ECU is for the right year of car, engine and transmission type. A Google search on the part number will find hits on this info.

P0135 is for the O2 sensor, Bank, 1, Sensor 1. This is a non-California trouble code. It is the first sensor on the exhaust system coming off the head.

Is the sensor at this location California or non-california?

The P0125 code is most likely linked to the above code. Solve the above code, this code may go away.

The sensor behind the converter may be the same for both California and Federal.