Problem with fuel consumption!

I have recently bought my first car of a nissan micra 1.3 K11 16v. I love the car to pieces with its dodgy clutch and rust on the door.

However, after buying it I have realised my fuel consumption was very poor, I filled my tank half way and then did around 40 mile and it was under quarter full!

At first I just thought it was the sensor in my tank messing up as it would go up and down, however now I have suspicion to believe it is the lambda sensor on the CAT, as I hear if these are not working properly the fuel consumption will be poor.

I have recently changed my air filter and spark plugs, which helped the speed and slightly improved the fuel consumption but compared to my girlfriends micra the fuel consumption is still very poor.

I also have a 1.3 with 15" 7J wheels (195/45/15) and i probably do with 15 euros thats around 12L (100 octane fuel) 160-170km. It depends on driving style, city or highway. But i get those numbers mostly in city driving with a few hard pushes to the pedal every now and then (goddamn the fuel price is high :p). So, thats around 7-7.5L maybe 8L per 100km (not bad for a 16 year old car with those rims). Let me remind you that tyre size drastically increases fuel consumption :)

In your case....i think you probably have a lambda sensor problem. Try getting another one, and if it's the problem, you'll see improvment.