DIC is bad at calculating MPG.

[eggsalad]

I have a '13 LT hatch with 1.8/5MT. I've owned it for 3 months & 3k miles.

My commute is 90% freeway, but on weekends I tend to meander, both city and highway.

I reset the DIC MPG with every tank. I also calculate MPG by hand with every fill-up.

The DIC readout right before I fill the car might read anywhere between 34-38 MPG. However, hand-calculating the figures shows that *every tank* has netted between 34.5-35.5 MPG.

(I'm not here to complain about MPG. Those figures are fantastic for a car rated at 26/35.)

I just wonder why the DIC info tends to be so optimistic. Does anyone know the data and algorithms used by the DIC?

 

[spacedout]

Do you always check its accuracy? I drove my 2012 cruze 95,000 miles and its DIC was always 1 low to 6MPG high. I've only put 3500 miles on my sonic so far, and its been as close as 0.8MPG high all the way to 5MPG high.

I believe some of this is due to differences in pumps, can be about 0.4 Gallon different kick off between pumps. I've noticed a difference if the front or rear of car is lower/higher as well.

 

[perrymk]

My dash reads 41.9mpg overall, but my calculated is 39.1mpg. I track every tank in Excel. The dash has always been 2-3 mpg high on mine.

2014 Sonic hatchback LT
1.4T, 6spd manual
32K miles

 

[The Champ]

The DIC readout right before I fill the car might read anywhere between 34-38 MPG. However, hand-calculating the figures shows that *every tank* has netted between 34.5-35.5 MPG.

On the contrary, I think your numbers show the DIC to be very accurate.

When you "fill" the tank - it's virtually impossible to get the same "fill" every time. Differences in the levelness of the area where the pump is located and the discrepancies from pump to pump will alter your calculations are just some of the reasons that the fullness of your tank will never be the same from fill to fill.

My personal experience with DIC's and their calculations has proven to me that they are very accurate. This is with over 300,000 miles of driving vehicles that have them.

Our gas tanks are only about 12 gallons. If you are off by a just a half a gallon of gas on your "fill" after 350 miles it can change your actual mileage by 3.5 MPG. 350 miles with a 10 gallon fill is 35 MPH - with 9.5 gallons it's 36.84 and with 10.5 gallons it's 33.33 MPG.

Trust your DIC...:banana:

 

[Flyer]

The mileage is figured in the ECM. It knows how much fuel is used, because it knows with great accuracy how much air is consumed. Not to mention it knows the flow rate of the injectors at a given fuel pressure. It even has sensors (o2 sensor) to ensure that it's not using to much fuel or to little and makes adjustments on the fly.

The pumps are different and probably not all that accurate. The level of the car varies so there may be air pockets in the tank. The amount it will swell may depend on the temperature of the plastic.

However to play devils advocate .... ponder this one .. how accurate is your speedometer. It's inaccuracy will throw the odometer off. If the odometer is off, you will NEVER get an accurate mileage reading. If you revert to GPS, that will only measure distant as a flat line.

 

[perrymk]

how accurate is your speedometer. It's inaccuracy will throw the odometer off. If the odometer is off, you will NEVER get an accurate mileage reading. If you revert to GPS, that will only measure distant as a flat line.

On my previous car, when the speedometer read 70 the GPS would read 67-68. If I came across one of those 'you are going this fast' standalone sensors on the road that displays speed for all to see it too would have me 2-3 mph slower than what my speedometer read.

My Sonic is right in agreement with both my GPS and the sensors I occasionally come across. I assume it has something to do with going from dial speedometer to digital speedometer but don't actually know.

 

[Flyer]

I was waiting on someone to bring GPS into it ...

GPS measures distance across a flat plain to measure speed. So ... if your road was perfectly flat then GPS would be ideal. However with a hill, the sensor isn't moving flat, so some of that distance measured is energy moving either up or down the hill, taking away from the flat movement.

Hard to describe in words, but think a right triangle ..

For illustration purposes:
https://en.wikipedia.org/wiki/Right_triangle

The GPS measures the distance of the top side on that triangle. While the vehicle is moving between points A and B, the GPS is measuring distance between A and C. We all know the distance between A and B is further than between A and C. Thus ... an inaccurate speed reading.

Oh and radar units are suppose to be calibrated daily for accuracy by using a tuning fork.

Disclaimer:
Only playing devil's advocate. For me the DIC is well enough to know if I'm getting decent mileage or not.

 

[Stew]

As others have mentioned, it should be pretty darn close. The ECM knows the injector on-time and it knows the flow rate of the injectors so it's simple math to know how much fuel has been consumed and how far you've driven. But, the measurements are pretty small for things like injector on-time and the on-time happen tens of thousands of time so even small rounding errors will add up and throw it off a little.

As an aside, you can adjust the MPG calculation with HPTuners to get that a little more accurate if you want, but the cost of HPTuners would hardly be worth it just for that.

 

[tdiller]

I have a '13 LT hatch with 1.8/5MT. I've owned it for 3 months & 3k miles.

My commute is 90% freeway, but on weekends I tend to meander, both city and highway.

I reset the DIC MPG with every tank. I also calculate MPG by hand with every fill-up.

The DIC readout right before I fill the car might read anywhere between 34-38 MPG. However, hand-calculating the figures shows that *every tank* has netted between 34.5-35.5 MPG.

(I'm not here to complain about MPG. Those figures are fantastic for a car rated at 26/35.)

I just wonder why the DIC info tends to be so optimistic. Does anyone know the data and algorithms used by the DIC?

I just filled up this morning dic said 37.7 mpg. My cell phone app that I have been using since I bought this 2015 sonic calculated the mpg at 37.4 I have always been within a mpg or two calculated v dic

 

[SonicFlow]

The last handful of fillup's, the dic has been 1mpg over my manual calculation.

 

[spacedout]

Just like my cruze the sonic I've seen it claim 6mpg high or even 1MPG low. Sure some of this can be attributed to pump differences, but I say on average is 2-3MPG high all the time. You really need to do the math when you fill up if you want any form of accuracy.

 

[mja]

As others have mentioned, it should be pretty darn close. The ECM knows the injector on-time and it knows the flow rate of the injectors so it's simple math to know how much fuel has been consumed and how far you've driven. But, the measurements are pretty small for things like injector on-time and the on-time happen tens of thousands of time so even small rounding errors will add up and throw it off a little.

What this means to me: if injectors run static and we're demanding over 100% duty cycle we can get better MPG at WOT than stock. :banana:

As an aside, you can adjust the MPG calculation with HPTuners to get that a little more accurate if you want, but the cost of HPTuners would hardly be worth it just for that.

This is a really nice feature, I remember adjusting the gas gauge so it showed actually how much was in the tank, and not some ridiculous percentages at diff levels that no one understands.

 

[Yosemite Sam]

DIC is about 13% off from calculated values.

 

[wekam]

My scangauge II is showing about 2mpg higher than the DIC readings.

 

[JesusTheAgnostic]

Mine is always about 2-3 mpg higher than the mpg that I calculate by hand. I always use the same pump and fill up with the same type of fuel. I would not throw percentages into the mix and say that it is 10% off or something like that because it doesn't matter if I average 29 or 42 mpg it always reads between 2-3 mpg higher, and the percentage would be off. Either way still pretty good mpg, I just wish it wasn't so low in the city.