Fuel consumption
2003 civic (ill answer for engine, not dragging brakes, or seized wheel bearings etc)GOT THE check engine lamp out, driving.? NO bad. scan it.get it scanned yet to see if there are DTCs stored?we scan regardless of any CEL status. what id do, is get my own real scan tool for like $9 (ask)and scan it.then see if it holds Closed Loop status hot. if not?, fix that first.if it holds CL at idle hot, then i check 40mph light flat cruise.holds CL. (closed loop) if not IT WILL SUCK gas.ever put a new cam belt on this engine. if not bending all the valves in the head is next. $1500 bill. or more.never skip the cam belt.i bet your engine is not working in CL, at all.i discover that, and then work that problem , idle CL failure is themost easy to work, its parked.1: i check compression over 150PSI x4 and done at WOT, wide open throttle (pass or fail)2: i check spark at all spark plugs , 03 timing is fixed.3: now i check fueling,i look at my live data from my scan tool and see that all senors read right but my front 02 sensors is rich all the time. i check fuel pressure, its at spec,(35?psi) not 60 no 10, not 20i do the injector leak down and balance test in the FSM.it fails. i fix that.it passes. i now put in a new front 02 sensor. bingo fixed.Think of CL as MPG, NO CL , NO MPGCL is is also called Stoich, and is the max ifficency point of the fuel air mix.