CL9 Fuel Economy gone bad

[falco]

I have a 2003 Honda Accord Euro, Automatic and its done 208,000 kilometers.
My fuel economy has gone from 9 to 12 liters per 100k to 14 to 17 liters per 100k
So far I have changed spark plugs and changed Auto tranny fluid, and changed engine oil and filter.
What I anticipate doing but haven't done yet is, change fuel filter, and maybe get the main drive belt looked at. Also the main drive belt idler bearing.
The reason I am looking at the belt, its looking a little "blue" in the middle of the belt and its left a tell tale line of something on the bonnet soundproofing






Can anybody suggest anything else I could look at, that may be affecting fuel consumption.
Or; I have been considering buying a later model Euro and passing my CL9 down the line.

[u mad?]

o2 sensor

[Daveho1]

^^this

[u mad?]

^^that

[Daveho1]

^^^those

[u mad?]

^^them

[Daveho1]

^^^they

[AndrewRox22]

^^these?

[Daveho1]

^^bbk

[Daveho1]

Or have you been transporting progressively fatter people around

[Martin77]

Anything unusual in the running of the car (noise, vibration, etc...)?
Mechanics should be able to work out faulty components through the obd2 port (such as oxygen sensor).

[Daveho1]

^^^ O2 sensors generally dont throw a CEL.
Unfortunaly over time they just go bad, sometimes it's as easy as build up on the sensor stopping the sensor reading correctly but really they need to be replaced.