Fuel Used Indicator Reports Lower Fuel Use After Tune

[sliwis]

U7185-9r05

I love the performance and drivability of my 2005 Chev 2500 HD Duramax. I run the 65 HP tune and truck runs great.

The fuel used indicator display now reads less fuel used than on factory tune. I see three gallons difference after numerous fill ups. Is there a correction or calibration change to fix fuel used display? This also affects fuel economy readout.

Regards,
Stan

[mikel]

These readouts are nototiously inaccurate with performance tunes, best bet is to log actual mileage vs fuel used and do the math manually.

[sstimothy]

I was just going to post this same question. My truck has a 26 gallon tank and I ran it from full, to low fuel (usually takes about 22 gallons to fill back up). Since installing the tune and reseting the fuel used, it only says I have used 15 gallons on a whole tank which makes my MPG eneriously high. Here I am telling everyone that I'm getting 25 MPG when I'm only getting about 17. Is there a fix? Is there any other measure in the DIC that is incorrect. It looks like the odometer is reading right so I'll have to do it by hand from here on out? That explains all of these guys posting pics of their "new, better mileage". Wierd.

[bigdawg04]

I know , you would think there could be something in the tunes to correctly calibrate these settings

[kcole683]

These readouts are nototiously inaccurate with performance tunes, best bet is to log actual mileage vs fuel used and do the math manually.

Strange. I run my 2007 LBZ on the 65 tune and the fuel used indicator is within 1% of actual.
The last two tanks were:
used display= 22.5 gallons pumped was 22.6?
used display 9.3 gallons pumped was 9.24
I always fill slowly and wait on the foam to dissipate & fill all the way to the top of the filler neck.

With this tune it is more accurate than the factory tune. Factory was usually within 2-2.5 %. I will have to experiment with the other tunes and report back.

[Trotorx2]

Mine shows 3 to 4 gallons low too. I thought I was getting the increased fuel mileage with the tune also but doing the math...nope.

[kcole683]

I am currently running the 120 tune and it definitely screws up the DIC fuel meter. It appears to show about 25% less fuel used than actual. I will fill up here in a day or so and verify. This of course shows a 25% error in MPG.

I've also noticed that to correct the Speedometer & odometer I have to adjust the tire size to different than what is on the truck. This if not done will also effect MPG readings.
My tire size is 245 75 16
if I set the tire size to 235 75 16 I get within .1 mile in 10 miles. or 1 mile per 100 error
If I set the tire size at 230 75 16 it is within a few feet of the mile markers in 10 miles.

I wonder why this is ? I would think the predator calibration would be closer than this.

Speedo calibration hint: The mile markers on your local interstate and a stop watch is better than a GPS for tweaking the speedo error. 60 MPH = 1 mile a minute.

The GPS only will work good on a perfectly flat road. It is however fun to play with.

[Trotorx2]

Yeah I agree with the speedo calibration. I had it close when I had the 16's but since I switched over to 17" wheels It is way off and If I get it close it sets off the ABS light.

[kcole683]

120 Tune read 25% less fuel used than actual giving overly high MPG readings.

I have run the 65 HP tune on my 2007 LBZ for about 6 weeks straight now. I fill up at the same pump every time and always fill all the way up to the filler neck,waiting on all foam to dissipate. On the 65 HP tune in my case it always shows within .1 to .2 gallons of what I actually pump.

Anyone else this accurate ? This tune comes out more accurate than the stock tune.

[odlaw]

My gallons used have always been less than 1 gallon difference. I always hand calculate anyway, so the inaccuracy of the tire size calibration is of more concern to me. I'm running 265's on stock 16's - the closest I can get is setting it to 245's - even then it's one MPH off. If I set it to 265 it's almost 4 mph off.

S/N 7F00FDAA
v.9r11

[slick]

my 2005 lly is of about 2 gallons per 10 gal.

[superredhawkhunter]

Not all tires have the same circumference and tire wear will change the accuracy a little. Also GM had plenty of trouble with their instrument clusters malfunctioning and speedo's being off is the major offender. They have a special policy on this issue.

[jevanb]

mine is always right on
and I always fill to top of neck