MacDaddy (jdm 1.3 engine swap in my 1999 honda civic)
 

I put a jdm 1.3 engine in my 1999 honda civic hatchback, hoping to get the promised 50 t0 60 mpg. After my first tank of gas, I only got 28 mpg. The folks that sold me the engine said I should use the Throtle body off the 1.6 from the old engine. Any thoughts, or ideas about this disappointment?

Welcome to the site Mac Daddy.

Do you have all the wiring and ecu for the 1.3? I'd imagine you would want to use the throttle body from the 1.3 vs 1.6. I am no Honda expert though.

Mac Daddy
 

Thanks for your response, Because the sensors and ecu are different in Japan, I was told to use the harness and ecu from my 1.6 and that it would run fine. I did make one change, I took the crank position sensor from the 1.6 and put it on the 1.3 in order to keep from having to rump the pins for this sensor in the ecu.
The engine runs well and I can't even tell a difference in the power between the two engines.
I'm not sure if the 1.3 throttle body will work on the intake manifold of the 1.6,
I was told I had to use the 1.6 manifold because of US polution sensors, there seems to be some difference between the two bases although either one will fit on the 1.6 manifold.
I'm wondering if the winter gas formula would make a lot of difference, I always notice a difference in the winter mpg but not that much, I normally get 35 to 37 mpg not 28.
What if I try higher octane gas?

Mac

Any more progress on sorting this out?

It's not likely the gas. There's slightly less energy density in the winter blend. Not nearly enough to account for the difference you saw.

Given you dropped from 35-37 to 28, there's something else going on.

I don't have experience with hondas, but it may take a couple tanks for the ecu to learn the new operating conditions. The ecu doesn't know what size the engine is.

You will definitely need that Ecu from the 1.3 car. Otherwise you'll be lucky to get any gains.

Higher octane won't help either. Unless your detonating but I doubt it.
You need the complete intake and Ecu from the 1.3 to get the mileage that the 1.3 is rated for.