For some time, we have been seeing very erratic fuel economy. The engine is in very good condition and we maintain it carefully. But every time we put gas in, the MPG changes. Two recent trips: first leg on highway, 27 mpg; return leg, 33. Next trip: first leg, 27; return leg, 35. This pattern happens continuously, dramatic swings in economy, same day, same road conditions. By process of elimination, it can't be getting the occasional bad tank of gas, because this has been going on consistently for almost a year. Sometimes the highway MPG gets as low as 25.6, and as high as 35.8!

We had a problem for a while with the mysterious check engine light. Several Honda dealers worked it over, no answer, EGR valve replaced twice. Hasn't happened for some months, since Morehead Honda switched the coil packs around (but none were replaced).

What could be causing these wild swings in performance? Bad 02 sensors? Have also heard that the Evaporation Emission Control Canister might be the culprit. Appreciate your thoughts, regards, Steve

 

if your getting better economy on different legs of a trip, id look at elevation changes on the road. if you're always getting worse mpg in on direction, is it all uphill?

and I'm a little concerned about a dealer just switching coil packs around. Sort of like trying to fix low compression in 1 cyl by moving the rings to different cyls. If one is bad, it's bad. period. moving them around isn't going to fix anything, it's just going to change the problem, and probably make it harder to diagnose the next time.

 

I've been tracking the conditions. No differences in wind or elevation that would be significant. The factor which changes the fuel/air mix raito is simply putting fuel in.