I am averaging 33.5 mpg mixed but I wondering how accurate the dic is?

see the links ...
http://www.youtube.com/watch?v=8PAT5g-apjc

http://www.youtube.com/watch?v=hpygYNkLcOI

:)

It is very accurate if you reset it occationally, usually at every fill up.

that video was after I just filled up ,reset and drove about 50 miles on cruise on flat terrain!

Obviously your numbers are going to be skewed right after it's reset, but after about 200 miles or so it gets you a pretty accurate #

so far mine systematically reads high

http://picsorban.com/upload/mileage.jpg

its still close enough for me. the only way to really know is to read the injectors and how much they are spraying and then factor the miles you went.

its still close enough for me. the only way to really know is to read the injectors and how much they are spraying and then factor the miles you went.

thats how the DIC calculates the mileage I believe, summation of injection quantities

So far the DIC is routinely high, but my sample size isn't that high yet though. Long term statistics should negate almost all error in re-fueling quantity. Although right now the difference is less than 5%, and if it stays that way I would be very pleased since under 5% error is very small.

yeah i would agree that 5% is a small amount. how long are you planning on testing?

Realistically...until I get bored of it lol.

haha nice. since people are pulling great numbers from performance tuned cobalts i wonder what the XFE will get?

Mine is generally 2-3 mpg higher than actual!

thats how the DIC calculates the mileage I believe, summation of injection quantities


Correct - the differences arise based on sudden changes in driving habits, as well as differences in what the injectors are actually spraying vs. what the computer thinks they should be spraying.

That's why the tuned guys rarely have an accurate DIC. There was a time when the dealership reflashed my car, and it thought it had stock injectors again when it didn't. In 1 tank of driving, my readout when from 26.5 to well over 30, even though my actual mileage did not change.

I get 27-28 average with my 60's! :) And got almost 40 on my 1200 mile drive from MO to NC

I get 27-28 average with my 60's! :) And got almost 40 on my 1200 mile drive from MO to NC

Per the DIC or your own calculations?

differences in what the injectors are actually spraying vs. what the computer thinks they should be spraying.

That should be the main source of error, esp. in LNF applications. Fluxuations in rail pressure due to non-constant fluid compression makes it hard to get exactly the right amount of fuel out, but Bosch does a very good job with tuning the fuel systems. I think error I've seen w/ diesel is usually only 1-3%.

That should be the main source of error, esp. in LNF applications. Fluxuations in rail pressure due to non-constant fluid compression makes it hard to get exactly the right amount of fuel out, but Bosch does a very good job with tuning the fuel systems. I think error I've seen w/ diesel is usually only 1-3%.

Mine's reading 25.4 at the moment, and once this tank is gone, we'll see exactly how accurate it is. :cssNET:

Do people seriously think their hand calculations are more accurate than a system that can track distance, and amount of fuel down to a T electronically?
The car tells you how far you've driven, and the car tells you how much gas you have, and how much you're spent.
How hard is it for a computer in 2008 to do the simple math of averaging? It records how much fuel is sent to the engine, how much is in the tank, and how many miles the car traveled.

Do people seriously think their hand calculations are more accurate than a system that can track distance, and amount of fuel down to a T electronically?
The car tells you how far you've driven, and the car tells you how much gas you have, and how much you're spent.
How hard is it for a computer in 2008 to do the simple math of averaging? It records how much fuel is sent to the engine, how much is in the tank, and how many miles the car traveled.

Read the posts above - the computer is only accurate as the data it is given. Fuel injectors are rated to flow a certain amount at a certain pressure, and that's what the computer uses. However, said injectors don't always flow exactly as designed, and can throw off the numbers.

The amount recorded in the tank is also just a float attached to the pump that records the fluid level. This is why it may stay "full" for 30+ miles after you fill the tank, why the gas gauge can move when you go, stop, turn, etc.

You place too much faith in the system...

I trust the accuracy of my speedo on stock tires and a closely monitored gas pump, as well as my ability to determine mileage from that data, than I do with my car's computer.

also in addition to the above post:

if, after long term data taking (where the error in fuel-adding method goes away) the DIC reads higher on average, that means the CPU is bullshitting us, but we will have to wait for that

Since I got my 06 SS/SC in june of 06 it has ALWAYS read 2 mpg to the high side.

Example:
DIC 32.8
Actual 30.8

my last fill up the car DIC was actually 27.6 and my hand calc said 27.6...

IT DIDNT READ HIGH!!!!!

On my first fill-up, it read about 2mpg above what I actually got.

I observe about a 4mpg difference with the DIC being much higher

I observe about a 4mpg difference with the DIC being much higher

You probably also have injectors that aren't even supported by the PCM. You're lucky you're only off that much. :lol:

ah i dont look to often, i just fill it up at half tank lol

My 2008 G5 L61/F23 is always spot on when comparing the DIC to the measured amount. Or at least within .2 so far.

My 2007 G6 LZ4/4T45 is always 1mpg optimistic compared to the measured amount.

lol at the first vid. the guy says this is after 50 miles *presses button* 49 miles. hahhaha

With 60# injectors, my DIC is WAY off. On a highway trip of 190 miles, it read 37.1MPG. The actual calculated MPG was 30.4.

My DIC is kind of quirky. When I am at idle after driving, the MPG will slowly tick down. So if it said say "27.5" mpg after sitting at the light for a while, It will start ticking down and get to 7.5 ish after while.

This happened after I took my car to get fixed for the fuel sendor. Anyone have any idea what this is all about?

My DIC is kind of quirky. When I am at idle after driving, the MPG will slowly tick down. So if it said say "27.5" mpg after sitting at the light for a while, It will start ticking down and get to 7.5 ish after while.

This happened after I took my car to get fixed for the fuel sendor. Anyone have any idea what this is all about?

Is this right after you reset the MPG on the DIC? If so that is normal. The DIC calculates average MPG. Every time you reset it, the MPG starts averaging from 0 again. Once you get 100 miles or so on the MPG calculator you won't be able to see it drop but maybe .1 MPG if you sit at a light for quite a bit.

My DIC is kind of quirky. When I am at idle after driving, the MPG will slowly tick down. So if it said say "27.5" mpg after sitting at the light for a while, It will start ticking down and get to 7.5 ish after while.

When you're idling, your mpg is zero, so yeah, your average reading is going to come down. If you haven't reset it recently, it will usually take several minutes before it changes.

Reset your trip counter next time you fill up and then when you fill up the next time look at how many gallons you put in your tank and how many miles you went. after that take the number of miles you traveled since your last fill up and divide them by the number of gallons you put in your tank. That should give you your exact MPG. Then you can compare it to your DIC...

I've noticed mine is almost always 1 mpg higher than what I actually get. I haven't done a spreadsheet on it but I've got 6k miles on her already. Fill up every 3 days driving the same loop and for the last month the DIC says 30.5 - 30.9 depending on how hard I drive. My calculated has always been 29.4 - 30.0

BP Amoco Ultimate 93 octane

Even when you calculate your MPG yourself, there is error. The error is in how much gas you put in your tank. From tank to tank, neither yourself nor the pump will shut off at the exact same spot in the tank every fill. It's close, but not exact, therefore you'll get some error in your calculation. I'm sure we've all added a tenth or two gallons to get that price to the nearest dollar etc. That extra error on top of the pump's auto shutoff not being identical each time.

You're probably realistically within the error margin of +/- 0.5MPG even when you do it yourself.

I top my tank off...All the way to the edge of the fill tube lol

I top my tank off...All the way to the edge of the fill tube lol

This is very bad for the car and you should not do it.

it doesn't hurt anything...

Actually it does. Its not good for your carbon canister which takes fuel vapors and injects them into the intake manifold instead of letting them leak into the atmosphere.

As far as mileage I think the DIC is pretty accurate. At first it was off by about 2 mpg and had lots of fluctuation because of a limited mileage amount and depending on city of highway driving. I haven't reset it since I bought the car (8,100 miles) and it says 27.4 mpg. My own calculations say 27.25.

o well that's the way I've done it since I was 16 and I've never had a problem. Not to mention for some reason with this car at every gas station the damn pump clicks off and i can still fit 3 gallons in my tank so if I want a full tank I gotta top it off.

The DIC is... optimistic on my car. Almost always 1-2mpg high