92 civic dx with d15z1-p07l01 with d16z6 harness no egr only getting 35mpg

[needap07-l01orl02cali-ecu]

Ok well i have a 92 civic dx with dx trans d15z1 p07l01 cali ecu d16z6 harness no egr other than that all stock dx but i deliver pizza amd im averaging 35 mpg for about a month i was rilunning without the vtec harness and averaged exactly the same and when i put the harness on i couldnt tell much of a differance with the vtec i cant hear nor feel it at all i understand its not like other vtec in that sense but the cel went off but no noticeable differances i was expecting atleast 40mpg any help would be greatly appropriated

[Chrysler kid]

The z1 operates in 12 valve mode until vtec engages which makes all 16 valves open. It only effects performance

The egr valve controls lean burn.