it could be done if the wiring was done properly. i also had to fix my wiring. the best approach towards solution is, if you done the engine wiring properly, you can buy un-cut wiring from engines market, and then get it joined with the car's wiring with some good electrician.
There could be many reasons for bad fuel consumption, but first you should sort the problem of wiring, because in these efi engines, there is a brain(computer), which takes decision for utilizing fuel. And if brain is not getting input , it cannot made good decision.