I think the miscalculation from the MPG guage on our trip meters is courtesy of the calculator it uses to get its reading for our trip MPG... the maximum MPG it can read is 150.0 MPG... i tested this in the "EV only" mode where people are saying the fuel injectors and valves are certainly closed... Once i hit the EV only mode, i reset my trip meter, and it quickly read 150.0 mpg and wouldnt go anywhere below or above this number, until after i had stopped once and then started going again.

In this mode, for sure we are getting way over 150 mpg....



So would this miscalculation cause the other miscalculation? probably

any other input anyone?


p.s... sorry about my confusing explanation, i cant translate my ideas to paper for the life of me

 

Sorry Clemert,

that is very unlikely to be the reason. We are quite sure Honda calculates in metric units, such as L/100km, then converts it to mpg only for the display. We are also quite sure that average FE is not calculated by averaging the instantaneous FE over time. It rather accumulates the total liters (or milliliters) spent, then divide by kilometers driven. (Then converts to mpg, if necessary.)

This bias in FE display annoys me as much is it annoys you. I once thought it had to do with the "calibration" procedure that takes place every now and then when engine load is low. The FE display then suddenly goes from almost zero to some value between 5 and 10 L/100km. However, I am pretty sure this isn't the case, beause it happened a few times just after a reset of the trip odometer, and average FE continued down, even during the calibration.

I am also thinking it might have something to do with the evap system in the tank. Maybe the control unit can't compensate fully for the released fuel from the canister. Or it overcompensates.

If you find out what the reason is, or if you could find some pattern in the bias, let us know. Maybe we can figure it out eventually. Otherwise it's just a plain bad calibration, only that 4% as on mine seems too much.

Best regards,
Rolf

 

I have yet to see any manufacturer calculate running trip MPG accurately. Both of the BMWs that I have owned would notoriously over estimate trip MPG to the tune of 10% error. BMW has been putting instaneous and average MPG guages in their cars since the 80s - you'd think they have it right by now.

If I were to guess, I would venture that the error is largely caused by the difficultly of accurately measuring car fuel flow. I can imagine that constant change in pressure and speed of fuel flow (unlike a gas station pump) combined with a mechanical meter that has to speed up and slow down some moving part with the changes accumulates error.

I like the fact that my HCH II at least under estimates average FE. Has anyone ever seen it over estimate their FE?

Here's another important question: How much do you trust the accuracy of dividing tank miles by gallons used? Has anyone verified the accuracy of the odometer in the HCH?

 

I understand that all HCHI's (first generation) were OVER estimating MPG. It's just the HCHII's that under estimate. What's interesting is how consistant it is! Almost everyone reports the same error. If the system can be ALWAYS off by the same amount, it's got to be a calculation (calibration) error. For this reason, I belive it IS able to correctly report fuel flow... it's just using the incorrect calculation when it displays a number.

You'd think they could get this right! You'd also think this is correctable with a new calibration they could load into the computer with their scantool. Perhaps, someday, they will do this!

 

It overestimated my FE by .6 mpg on one tank. Every other tank has been underestimated. So, that's 20 tanks underestimated to 1 overestimated. The overestimated tank included a LOT of traffic jam time, so I wonder if that had anything to do with it.