Speed=Poor Mileage

[WhiteDuramax]

I had to go to Indianapolis today for a metting about a 110 miles from where I live. Well I filled up on the way and on the way back, I was late on the way so I was runnin about 75-80mph the whole way there and about 75 on the way back. Filled up at a Fylin J on the way back for $1.28 (pretty cheap) even though the sign said 1.22, must have been for the bigger rigs, I had 126 miles on the tripmeter and put 11.64 gallons in it. That equal out to about 10.8 mpg, very poor. When I filled up the first time my mileage was 14.5 mpg which was all back road driving and playin. So more speed equals less mpg of course. Just somethin to talk about.

[RichBailey]

Hmmm, somethings wrong there. Last month I drove to Tucson from SF Bay Area with cruise control at 80-82 mph. Got 18 mpg with first tank (707 mi, 39.3 gal), got 18.5 mpg with second tank (564 mi, 30.5 gal), and only got 17 mpg with 3rd tank due to strong headwinds. This is with hot juice set on 4. Truck really wants to run at 80-85.

[WhiteDuramax]

There was a really strong headwind on the way there and I dont have any performance boxes. Still I wouldnt think it would be that much of a difference.

[GMC-2002-Dmax]

Road Trip,

CT to Outer Banks, NC - 80 mph avg the whole way -there and back - Hot Juice L4, 19.5 - 20 mpg there and back.

I had stock 245's on for trip with windows up , AC on low, and a tonneau cover.

Wind, what's that :D

GMC ;)

[WhiteDuramax]

Ok, I guess the question is, why is my mileage so bad??

[Rebel_Horseman]

For whatever reason my truck doesn't get that great mileage especially if i let it idle for any length of time. It too me a half a tank of fuel to get from Baton Rouge to Marshall, TX which was about 18.5 mpg at 75. The next trip up there I only got 16.5. My truck is not consistant at all.

[FirstDiesel]

My truck is very consistant.

I get 15.5-16 MPG average. I get 14 if I do no highway driving during the tank full. We just got back from KY. Trip there was 650 miles and we drove around 75 mph. Got my normal 15.8 mpg. Trip back I ran a little faster at times. Mileage was 17.2 mpg!!! This is the first time I have ever broken 16 MPG.

[typecast]

FYI, I've seen my highway mileage as low as 14 driving 75 into a strong headwind. Driving 65 no headwind I can get as high as 23.

Stong midwest headwinds make a huge difference. If you try to maintain speed, mileage goes in the toilet.

[Kennedy]

WhiteDuramax,

Start poking around with the Predator in the injector balancing data. Follow the engine noise thread fo reference.

[JEBar]

In the area of MPG, high speed is definitely the enemy of my 3500. Interstate travel at or slightly above the posted limit usually yields 16-17 mpg. Recent cruise from Raleigh, NC to Knoxville, TN and back with cruise set at 1900 rpm which equals 64 mph yielded 20.4 MPG ..... hard to keep her down that low but doing so certainly helps the pockebook ... Jim

[WhiteDuramax]

Checked the balance rates and pwm's?, Dmax-Allitech said they were good, now alls I am worried about is the lopey idle.