Honda Accord Engine Problems
Accord Euro ant invasion
I have never heard of ants invading an ECU before, it's not something we have heard about here at Carsguide. I find it hard to believe that ants could, in fact, get into an ECU that is located in a position that isn't exposed to the elements, including ants. I would have thought Honda might have been interested in at least checking your car to see how the problem occurred.
Euro break down
Unfortunately it would appear you are dealing with an incompetent or deceptive dealer. Ask to see proof of what work has been done by the dealer, and have them justify their findings to you. I would also take the case to Honda direct and demand head office intervention. Also consider taking your case to consumer affairs.
Honda Accord CO2 sensor
Honda claimed an overall average of 9.2 L/100 km, but that's derived from a lab test and not real life. Even so it should be an indication of what you could expect, and that seems to be mirrored by your real life results. It would seem that it's probably running rich and your theory of a faulty CO2 sensor could be on the money. Your dealer should be able to check it and confirm if it's a problem or not.
Unleaded for my Accord?
Most engines are optimized to run on one fuel or another, and that's the fuel they run best on and deliver the best fuel economy, but they also have 'knock' sensors that detect pre-ignition and adjust the ignition timing to avoid it. That means that while they have been optimized to run on one fuel they can also run on another, lower quality one. Generally your car will run better on premium unleaded than they will on regular unleaded. But we were let in on a little secret and that is that the regular unleaded we are buying is no different to the premium on sale. It seems it's more economical for oil companies to produce one type of fuel instead of two. What they do is guarantee the minimum octane rating of the fuel they produce, in the case of regular unleaded that's 91 whereas premium is a minimum of 95, they don't talk about the maximum octane rating. In that case we are wasting our money buying premium when regular is the same fuel. That was last week, what they will do next week is anybody's guess. Why do we pay more for premium? Simple, clever marketing by the oil companies that has convinced us it's better.
THE Accord is designed to run on regular unleaded and you won't have any problems with it if you do, but there are advantages with PULP. The engine's management computer needs time to adjust its settings to the new fuel so it may take a couple of fills to see any change. I wouldn't bother running it on PULP.