Fuel Average Reset, Now Gaining too Much MPG - any ideas?

[canamryder]

I cleared off my Fuel Average to zero, as expected. Then as putting in the miles it was climbing slowly as it has done before, as expected. Now it's going up and beyond 42+ mpg, NO WAY! Last year holding 38+ mpg., as expected the way I drive, mostly county roads, very little 60 mph and not on highways much at all. I reset twice now doing the same thing. Fuel gauge/mileage seems to be correct after about 70-80 miles, as it always has been. Any idea what could cause this?

[EdMat]

Year, model and mileage would help get you an answer.

[canamryder]

Year, model and mileage would help get you an answer.

Sorry about that! Ryker Rally is a 2019 with about 13,900 miles.

[Markubis]

I'm not surprised. The engine is broken in and you keep the rpms low by staying off the highway. I get mid 30's and I drive it like I stole it.....sometimes.

[Captainmal]

Got an education from this. You re-set the fuel mileage?

Did not know you could. Time time to dig out the book and learn how.

[pidjones]

I believe the mileage calculation is way off, and moreso right after a reset. It is a running average from the last reset. If reset just before very gentle operation, it will be high. If reset just before accelerating up a hill, it will show low. After about 200 miles it will average out closer to real, but in my experience always high. It was that way on my '86 SEi, my '08 SX4, daughter's '12 SX4, wife's '17 Equinox, and our '21 RTL.

[linguine]

I believe the mileage calculation is way off, and moreso right after a reset. It is a running average from the last reset. If reset just before very gentle operation, it will be high. If reset just before accelerating up a hill, it will show low. After about 200 miles it will average out closer to real, but in my experience always high. It was that way on my '86 SEi, my '08 SX4, daughter's '12 SX4, wife's '17 Equinox, and our '21 RTL.

I agree. 4 fillups during our trip [read that as 2 up] from Phoenix to Kanab Utah, then to Zion, then to Page, AZ, then home::> EACH leg showed us at 45+mpg. This is for 65 mph for very long stretches.

I actually was going to post about this, but this thread just came into view.

The fixed ODO with grand mpg shows 35+ mpg now. What to believe?

Yes, I read all the threads, etc about how to fill up, and then calculating by one's self from there. I find the fillup to vary by ~0.4 gal. That's enough variability right there for me to suspect hand calculations as well.

I'll assume the gas tank gauge sends a "filled" signal to the master GPU, and the calculations are based off the actual wheel-to-ground travel [rpm's, wheel circumference, etc etc].
Maybe that assumption is even off base.

[DickB]

I'll assume the gas tank gauge sends a "filled" signal to the master GPU, and the calculations are based off the actual wheel-to-ground travel [rpm's, wheel circumference, etc etc].
Maybe that assumption is even off base.

Unfortunately due to the Ryker's gas tank shape, the sending unit sends a "full" signal at anything over about 2/3 full. So the ECU can't tell the difference between mostly full and full full.

Fuel injected ECUs determine fuel used by how long the injectors are firing. This duration varies depending upon engine speed, load, and whatnot. Since the capacity of the injectors and fuel pressure is known, the amount of fuel squinted through them can be determined by how long each injector is energized.