PDA

View Full Version : Disparity in mpg between veh. computer/actual


stilly
06-05-2006, 13:59
I recently bought a 2003 Duramax 2500HD with 100,000 miles. The vehicle computer reads that I am getting 17-18 mpg, but in reality I am only getting 13 mpg. Why the difference in the reading?
DmaxMaverick
06-05-2006, 14:29
Is the tire size OEM? Are you using any type of a programmer/box mod? What on the truck isn't 100% OEM?
stilly
06-06-2006, 12:14
The tires - 285. The juice edge module was set at level three. Can I get more mpg by putting the module on level one?
DmaxMaverick
06-06-2006, 13:18
If you haven't corrected the odometer reading for the tire size change, it will be off by quite a bit with 285's (that's what I have on mine). The difference will be about 7-8% just from the tires. The Juice will also skew your mileage to the optimistic side on the DIC in most cases. You will have to calculate your mileage by hand for accuracy.

Lower levels with a power mod can generally improve economy. It all depends on how you use the power. Individual driving habits and conditions will have a bigger effect on it, though.
stilly
06-06-2006, 14:44
How hard is it to adjust the odometer to the tire size?
DmaxMaverick
06-06-2006, 15:10
How hard is it to adjust the odometer to the tire size?

Easy, but you'll need a programmer to do it. Predator, SuperChips, etc. For the money, Predator is the best option, IMO. You'll get a bunch of features with it the others don't come close to. Several of our Advertisers (http://www.thedieselpage.com/vendors/main.htm) carry what you need.

Even after correcting for tire size, you will probably still have issues with the DIC, due to the Juice. It will make hand calculations easier and more accurate, though.
BozDMAX
06-06-2006, 18:56
I am off about 1-2 mpg, with the DIC mileage consistently better. Stock tires. I never noticed a difference until AFTER I installed my Banks System, so I never checked things before to see if it had been accurate from the gitgo. Seems like someone mentioned the difference here on a board so then I started checking.

When my low fuel light turns on, I usually haved burned about 2-3 gal more diesel than what the computer thinks I have burned.

I can live with that small of a difference, but I would not live with the difference you are talking about. There are probably several other reasons for you to recalibrate for your tires.
50+
06-07-2006, 20:24
Mines usually off about 1 mpg, when I hand calculate. I get about 17 back and forth to work. Truck says 17.5 to 18 on the DIC. I have 265's on. But what I've noticed is that I usually put in more fuel than what the computer says its used. If I put in what the DIC says its used it would be darn close.
rob from bc canada
06-12-2006, 19:05
Mines usually off about 1 mpg, when I hand calculate. ..snip.. If I put in what the DIC says its used it would be darn close.

Right, but I suspect after a few such fillups, you'd be stuck on empty!!!

Mine is the same, the computer is off in the metering of the amount used, it's calculation of mileage based on what it thinks I used is correct.

Maybe they're trying to factor in some evaporation??? Or maybe we're not actually getting the number of litres (or gallons) we're paying for???

Surely, my $50,000 super-computer on wheels can't be wrong!!!
JeepSJ
06-13-2006, 16:26
One of the guys on our race team got burned by this over the weekend. His system said that he had 80 miles to go, and he had 40 miles to the next station that had diesel, so he kept going. He ran out about 3 miles short of the station.

Note - do NOT run a new DMax out of fuel. Self priming? Yeah, right!! It was on a Friday, so they called a dealer when it would not start. Service guy said to crack the lines and bleed 'em. Go look under your hood and tell me how much fun we had in 105 degree weather, with no shelter, trying to bleed the fuel system on his truck.

The display is only there as something to keep you from getting bored on long trips.
DmaxMaverick
06-14-2006, 08:54
Priming is not difficult on these....and certainly not worth a call to the dealer. They are not "self-priming", but are easy, nonetheless.

Open the bleeder (plastic screw on top of filter ass'y). Pump 'til you see fuel. Close bleeder. Pump up 'til hard. Start.

It will take a little longer cranking to start. If after 10-15 seconds of cranking and still no start, pump it up again. It will start.
JeepSJ
06-14-2006, 10:24
Priming is not difficult on these....and certainly not worth a call to the dealer. They are not "self-priming", but are easy, nonetheless.

Open the bleeder (plastic screw on top of filter ass'y). Pump 'til you see fuel. Close bleeder. Pump up 'til hard. Start.

It will take a little longer cranking to start. If after 10-15 seconds of cranking and still no start, pump it up again. It will start.

We did that...several times. Cranked until the batteries started to get low. That is what prompted the call to the dealer and they said to crack the lines at the injectors. After that, she fired right up.