To begin, you state in 40km you drove X amount of those kms in the city, filled up, and then drove X amount on the highway, and filled up again? Don't rely on the overhead computer for mileage. They can be +/- a good 20%. Let alone the fact that as much as the vehicle is electronically controlled, it can't compensate for low air pressure in the tires, headwind, tailwind, weight in the vehicle, etc. Now, for the engine tick, this is my other peeve with the EB35, is that Ford states it can run on regular (87 octane) petrol. Now, even with advancements in electronics and computer aided software to run these electronic engine management programs, when you boost an engine by either a supercharger or turbo, the engine is more susceptible to engine knock, or ping. Generally it's heard under mid to hard acceleration but at times can be heard when in a high or lower gear while giving the engine maximum fuel without it downshifting from a taller gear. History shows that these boosted engines require a higher octane fuel to help quell the engine knock. In say 120,000kms, the engine might require you to use a higher octane fuel, 89, or even 91 (most common with boosted engines) due to age. Not in all cases of course, and knowingly all dealers will fuel with 87 octane as that is what Ford recommends, but it's also the least expensive fuel you can purchase. It's really a judgment call on what fuel you want to use. Personally I'd stick with the higher octane, even 89 and see how that goes. Of course you'd need to get a truck on fumes, throw in a few gallons of 91 or 93 octane mixed with the remaining regular fuel to at least get a close 90 octane mix in the tank and see how the engine runs on that.