hi new to the forums, I was just really concerned about my fuel consumption
I already posted earlier at the 323/Protege/famillia thread, but here goes

Mazda 323 98-99 GLXi
16valve DOHC

4-6km/liter mixed
had tune-up done
has headers, muffler, filter and intake installed >>> does this make me consume more gas? I got the car with those installed already
or could it be something with the ECU or engine?