EF2 gas problems.

[kakaroto_ss4]

hi there.
ok i have a Civic Hach EF2 SI with a d13b FI engine swap from a honda logo look like the d16.

but my mpg is poor like 21mpgs on premium gas. ok i did this mod on the engine.

i change the header for the one that came stock on d15b 4-2-1, and the intake manifold to the same as d15b but i keep the same throttle body, the o2 sensor its bad i have to buy a new one and have a d15b M/T tranny. that all.

note: when the engine was stock its was the same 21mpg maybe 3 or 4 mpgs more but.....

help please.