Fuel Mileage mismatch

I've been using Torque Pro with an OBDLink MX for a few things, including measuring my fuel mileage.

According to Torque Pro, my average mileage lately has been ~22mpg.

Just fueled up, dividing odometer by fuel input got me 17.3mpg.

I have 32'' tires, stock was 31'' I think. My speedometer is dead-on accurate. 0.4Don't know if the odometer is accurate though. Even if my stock tires were 30'', the difference in circumference is only 6.6%, which would be 18.44mpg.

So what is more accurate? Why is there a disparity in my mileage numbers?

 

Torque has an MPG trim adjustment you may need to change under vehicle settings.

 

I always bank on what the hand math figures out at unless I've done major tire and gearing changes. So I'd check your vehicle settings in torque and adjust accordingly.

 

I'd have to guess the app is wrong, as said probably need to adjust a fuel factor.

 

Check your odometer with either GPS or by mile marker. Best to do at least 50 miles. If your speedometer is spot-on, your odometer is likely off. ScanGauge has both fuel and speed/distance correction factor. Set mine to correct the odometer as speedometer error doesn't bother me, would rather have accurate miles per gallon.

MPG is not always easy to calculate accurately. In addition to the above mileage error, it's hard to really get an accurate number for fuel used - different pumps shut off at different fill levels, and most people do not want to overfill the tank. Best bet is probably use Fuelly or a phone app, and get an average of several tanks. This will also vary with stop & go city driving vs high speed interstate vs lower speed highway. If my ScanGauge gallons used is within 5% of what the pump says, I call it good. Closest I've come on accuracy is consistent driving, such as 2 days of interstate at about the same speed.

BTW, most all of the OEM 6 lug Tacoma tires are about 30.5" diameter. BUT, mine lost a full inch when replaced at 37k miles, and they were not down to wear bars, which is another factor that affects the accuracy.

 

Ran some miles with my odometer trip zeroed with a distance traveled display on the GPS. Dead on accurate for 11 miles, the odo would have to have been off by 3.3 miles by then for the fuel mileage to be correct. Time to play with the trim factor.

 

ONLY accurate way is to top off your tank the same way every fill up. reset odo, then divide gallons used by miles traveled. Any other computer calculation is simply an educated guess

 

Lots of folks don't recommend filling tank past first click-off (fuel vapor charcoal filter), but every pump is different and even affected by how many people are using pumps at the same time. I do it on long road trips, ONLY if I'm immediately going to burn at least 2-3 gallons (truck will take 2.5 gallons from first click-off). No problems in 59K miles. Once you get trim adjusted, the only variation I see is from change in driving habits - more (or less) city driving, all highway, how much time idling in a fast food line, etc. My ScanGauge gallons used is usually within .5 gallon of what the pump says.

 

Also I found an option for a more accurate calculation using more sensors in torque, seems to be dead on now. Also it can calculate your actual volumetric efficiency, will post mine up tonight

 

Highest value so far is 83%. For the sake of searches, this is the volumetric efficiency for a 2010 Tacoma with the 2TR-FE, 4WD, manual transmission, stock intake. As measured by Torque Pro with an OBDLink MX.

 

Got 85% maxing the throttle at about 5k rpms.