How Accurate Is The Mpg Status?

[11Silvy]

I was just wondering how really accurate the DIC mpg economy computer was? It seems fairly accurate, maybe it's off by a small percent? Anyone have info perhaps. Thanks.

[old-chevy-dude]

I think it depends on how long between resets.. I haven't reset mine in at least 6 months and it has shown 17.2 forever hasn't moved up or down, but when I manually do the calculation at fill up I am closer to 17.9

 

I would say overall +/- 1 mpg

 

I haven't taken a long trip since July, and that was about 800 miles round trip and my manual calculations were 19.3 mpg and the DIC never moved above 18. But I pulled 600 miles out of 31 gallons (it took 31 at the fill).

[Bowtie2Sierra]

The MPG from the DIC was consistently .5-1mpg off on my truck when I used to check it.

[11Silvy]

Thanks.

[hfalconer]

I am going to say its off a bit as well. I have never tested it. However, I always compare the fuel used per the dic to the amount of fuel per the gas pump. I reset it each time I fill up and even taking into account some occasions where the tank is topped off, its been off. Sometimes a gallon or so.

[MaverickZ71]

The DIC on my '09 Silverado CC (5.3L 6 speed 3.42 gears) Z71 4x4 has consistently been wrong since new in regards to MPG and gallons used. It says I'm getting better gas mileage and using less fuel than I really am. After about 2 years of figuring actual gas mileage by hand, it has shown the DIC is overoptimistic by at least 20%.

 

I asked the local dealer if they could somehow reprogram or fix it so it would be correct and their response was "NOPE!".

[TheTrueMoron]

My DIC MPGmeter hasn't been off by more than .3 in the times that I've compared and it always indicated on the worse gas mileage side.

[Z45]

I find it extremely accurate in my vehicles and I never reset it. Doing so will throw off the mean so if you use a DIC reading with only 5,000 miles and then compare it to a hand calc using more miles, it will jive. It measures the fuel consumed by the engine and I cannot see why doing it manual would provide better results.

 

I would think that any discrepancies between what the DIC reads and what is calculated can be attributed to errors in rounding of numbers, Systematic errors.

 

 

All measurements are prone to systematic errors, often of several different types. Sources of systematic error may be imperfect calibration of measurement instruments (zero error), changes in the environment which interfere with the measurement process and sometimes imperfect methods of observation can be either zero error or percentage error.

 

 

Measurement errors can be divided into two components: random error and systematic error.[1] Random error is always present in a measurement. It is caused by inherently unpredictable fluctuations in the readings of a measurement apparatus or in the experimenter's interpretation of the instrumental reading. Random errors show up as different results for ostensibly the same repeated measurement. Systematic error cannot be discovered this way because it always pushes the results in the same direction. If the cause of a systematic error can be identified, then it can usually be eliminated.

[Garrett Street]

^^^ I would have to agree. It was extremely close when we took our trip to Florida last year. It was within +/- .5 the entire time. That's pretty good IMO.

[MikeInCtown]

On my 04, the DIC calculations were off by maybe 1mpg. I averaged by hand lust over 20mpg during a long trip once and I think the DIC had me at 19 something.

[Matt_]

The only time mine is off more than +/- .5 is when i dont go to the same pump and/or (remember im in NJ) the attendant puts more in after the handle triggers.

 

I'd bet that the DIC is actually the most accurate and the variations we see are due to different positions and sensitivities at the pumps.

 

edit: i reset the mpg every fillup as well

[MaverickZ71]

I find it extremely accurate in my vehicles and I never reset it. Doing so will throw off the mean so if you use a DIC reading with only 5,000 miles and then compare it to a hand calc using more miles, it will jive. It measures the fuel consumed by the engine and I cannot see why doing it manual would provide better results.

 

I would think that any discrepancies between what the DIC reads and what is calculated can be attributed to errors in rounding of numbers, Systematic errors.

 

 

All measurements are prone to systematic errors, often of several different types. Sources of systematic error may be imperfect calibration of measurement instruments (zero error), changes in the environment which interfere with the measurement process and sometimes imperfect methods of observation can be either zero error or percentage error.

 

 

Measurement errors can be divided into two components: random error and systematic error.[1] Random error is always present in a measurement. It is caused by inherently unpredictable fluctuations in the readings of a measurement apparatus or in the experimenter's interpretation of the instrumental reading. Random errors show up as different results for ostensibly the same repeated measurement. Systematic error cannot be discovered this way because it always pushes the results in the same direction. If the cause of a systematic error can be identified, then it can usually be eliminated.

 

 

 

The only time mine is off more than +/- .5 is when i dont go to the same pump and/or (remember im in NJ) the attendant puts more in after the handle triggers.

 

I'd bet that the DIC is actually the most accurate and the variations we see are due to different positions and sensitivities at the pumps.

 

edit: i reset the mpg every fillup as well

 

OK, I understand all that, and am glad that your DIC's seem to be working correctly, but on mine, it routinely says I've used 16 gallons when I really just filled it with over 19 gallons, etc. Most of my fuel is bought at the same pump at the same station (certified by the state within the last year), but I've also used about 20 other pumps over the last 2 years when traveling, with the same results. And it's physically impossible to add 3-4 more gallons at each fill up by squeezing the pump handle another time or two or three to top it off. I've even wondered if my PCM is calibrated for the wrong rear gears or something, but the local dealer says that not possible, and there's nothing wrong with the DIC in my truck, even though they've never even looked at it (just service rep brushing it off) Funny (or not) thing is, I was figuring fuel mileage by hand long before they invented a DIC, and the in-dash computers currently on a Ford and Buick in my family are spot-on.

[Matt_]

Mine was never 3-4 gallons off... somethings wrong there...

 

Do you have a wife or someone else that uses the truck that may inadvertently reset the DIC a day or so after you've gotten gas?

 

Edit: are you saying that its 3-4 MPG off or is it telling you "gallons used" and you're comparing that to how much you put in at the pump?

 

if the MPG is off by 3-4, try tracking your speed with a GPS and see if its close to what your speedometer says.

[MaverickZ71]

Mine was never 3-4 gallons off... somethings wrong there...

 

Do you have a wife or someone else that uses the truck that may inadvertently reset the DIC a day or so after you've gotten gas?

 

Nope, I'm the only driver/refueler/DIC resetter.

[Matt_]

^^See edit... i posted that at the same time