Diablosport Forums

I have an 07 GMC 4 x 4 running the 87 octane tune and the only thing that has been adjusted is the tire size. Well I do a lot and i mean a lot of highway driving probably 95% so i actually would like to have the DOD on for better mileage. I got my speedometer back in sink with my GPS so I don't believe that is not my problem. What speed does the DOD stop engaging in? With my cruise on running 74 mph it does not engage but I know it does engage at times running under 70. I drive pretty constant so I can't really figure out why I'm getting mpg fluctuations. It goes from 16.9 to 14.8 mpg. Any suggestions???

Sorry I forgot it is a 5.3 liter running crom 8r10.

Primed67 wrote: What speed does the DOD stop engaging in? With my cruise on running 74 mph it does not engage but I know it does engage at times running under 70. I drive pretty constant so I can't really figure out why I'm getting mpg fluctuations. It goes from 16.9 to 14.8 mpg. Any suggestions???

My tires/suspension are bone stock (SLE2 w factory suspension package). I must say, I do notice the DOD kicking in while in cruise control at 70+mph --- albeit mostly downhill and wind from the rear, LOL.

I have no expertise as to exactly WHAT triggers the DOD, or not. I am willing to try and levy a guess.

My gut says that it is driven by the torque/hp needed to propel the vehicle at a certain speed, as determined by various engine parameters monitored by the control system.

If the control thinks the engine can produce enough power to move the vehicle with 4 cylinders, it activates. Of course, there are lock out conditions, I'm sure, like accelerting from a standing stop, throttle change rate, etc..

As you say you have larger tires, that certainly requires more power at a given speed, all other things being equal, if for no other reason the added weight, and potential increases in rolling resistance.

That would be my guess.

Thus, it's not necessarily triggered by raw velocity, but rather a combination of things involving required torque/power at a given condition.

As to the fluctuation,, mine fluctuates as well, albeit not to the extreme your does. When ya got big "taares", that probably plays a big role in THIS equation, DOD or not.

here's some info on DOD that I found...

http://ls1tech.com/forums/showpost.php? ... ostcount=3

thanks, i appreciate the help!

I have less than stock tires and a lift kit, both of which hurt my mileage and DOD activation. I have a flat that I drive across that has less than 10 feet of elevation change (according to GPS) and the DOD doesn't activate there unless I have a pretty good tail wind. I see it come on when I'm going down hill. I really haven't noticed much difference in the activation based on the speed I drive, I'm usually in the 65-70mph range. As you do go faster you will have more wind resistance which I'm sure will not allow DOD to work. I have 4.10 gearing, but don't know if that makes any difference.

I have done the same trip on the same day with the same weather conditions at the same speed with and without DOD and with does give me nearly 2.5 MPG better. I think the more highway driving you do the more difference you are going to see.

I wish you could push a button and keep it in V4 mode longer. With the stock setup, it's hardly on as it is, so I don't see much benefit having it at all. I live in an area of rolling hills and mountains, and just don't see an increase with mpg on daily trips.

Currently I have it just turned off with the tuner.
Steven

yeah, I never considereed what happens in a hilly or mountainous area.... I live on a pool table where it's all virtually flat.

Excellent point.

I have both flat and hilly. Mines only on during the downhills, but I have enough downhills to make a difference about 1.5 MPG difference. I'm leaving mine on, any LITTLE bit of improvement is enough for me.