Cool plot! I can see your engine warming up, the idle fuel consumption goes down over time. It looks like an electric fan or AC is kicking on just after point 7.
Post a CSV so we can calculate an energy balance, or do it yourself. It would be interesting to plot energy-in (fuel ml/s * energy of combustion * some efficiency knockdown, make sure units are correct, multiply by the length of the time step to integrate), stored energy (mass of car * speed squared / 2, make sure units are correct; metric or slug-ft/s^2).
Then you can play around with "loss factors" to balance out the equation; Where is the energy going if it's not being stored in kinetic energy? Fit constant, linear vs. car speed, linear vs. engine speed, linear vs. fuel consumption rate (similar to BSFC), and quadratic vs. vehicle speed losses until the balance comes out to zero. This will be difficult to do, but educational I'm sure
