Why is my Fuel Consumption high compared to others of the same car model?

I own a Chevrolet Cruze 1.8 AT LS and I regularly record my Fuel Consumption at fuelly. I noticed that my average Fuel consumption is one of the lowest at fuelly. My car is regularly maintained and has around 40,000 km. I use my car for city driving in moderate to heavy traffic. My fuel consumption averages at 6-7KM per Liter. My brother owns a Honda Civic 1.8 AT and his car averages at 8KM per liter. Can someone explain to me why there's a a huge difference in fuel consumption between the cruze and civic? Is there something I can do to improve my cars fuel consumption?

Honda civic 2000 wasting too much gas?

What could cause this civic to waste too much gas. I had filled up the gas tank and it wasted in just two days. I took it to auto zone and they found the following error codes and said it was:
Sensor 1 heater system malfunction
Sensor 1 circuit high voltage
CSF sensor no signal
But none are supposed to cause a serious gas waste, and just recommended me lucas. Also the civic doesn't have a catalytic converter, I don't know if this is why. Is there something else I should check?

Honda Civic 2004 Check engine light coming on while going up hill?

So my Honda Civic 2004 has an extremely difficult time going up hill. If I start to climb a hill and my rpm's approach anywhere near 3600-4000 rpm's my car begins to do what I describe as "stutter up the hill." My check engine light turns on instantly. In addition to this, I can start going up the hill at 70 mph; however, when the "stuttering" occurs my gas peddal feels like it almost gets stuck and won't push any further (even though it can go further down) and my speed declines drastically and quickly. My check engine light will usually go off 24 hours after I return to a flat surface and have driven on the flat surface for about one hour. I can always tell when the light goes off, because the tension in the gas pedal is relieved and my car drives much smoother. I have had the code read twice, and the mechanic said it was throwing a different code each time so he is not sure what's going on. I have had new spark plugs put in and I keep up with my oil changes if that helps.

Do honda civic 2000 have catalytic converter?

OK I was wondering if the honda civic 2000 should have two oxygen sensors. But the problem is all the honda civics that are the same only have one and also doesn't have a catalytic converter. Is this a problem? I'm afraid this is the reason why the car wastes a lot of gas.

Misfiring car? Not sure what to do next?

I went to autozone and then ran a test on the code reader. I got back the P0303 or whichever one is the third coil. I tested the coil by pulling each cover off and testing the difference of each on the engines sound, no difference. So now I think it might be the spark plug on the third coil position? The car is a 2003 honda civic with 140k on it. Spark plugs haven't been changed as far as I know, bought this car used.

What do you think?

Thanks

Added (1). What I meant was that each time I removed a cover I heard a difference, so I've crossed out the ignition coils as a culprit.

Dealership won't change my transmission filter?

2002 honda civic 126,000 miles that had remanufactured transmission at 91,000 miles 6 years ago. Now i've done a fluid exchange every 2 yrs since then but i was now going to do a flush for $150 but the dealer says they don't remove the filter because it's sealed. Is this bad to keep the tranny filter in there for 6 yrs already?
I want the remaned tranny to last at least 91k like the original.