killfast1

Ok guys heres one for you.

Highway cruisin i get close to 26 mpg (figured on paper) up to 68MPH, then from 69-75 I get maybe 17MPG, then once i go past 76MPH im back up to about 26. Why the drastic change at 70? I figured this out by driving from San Diego to San Fransico several times. I made 1 trip at 68 (up and back). Then another trip at 70 (up and back). Then another at 85. I would also notice it while driving to work, about 150 miles round trip and as long as I kept it below 69 or above 75 I got good fuel milage. Anything in between sucked. I have had this truck for over a year and this has not changed. Any help would be appreciated greatly. 65 is to slow and 80 is a little to fast for southern California cops.


Yes I have been reading alot but have not seen anything like this on the site.

firestorm

I'm automatic, so that will make a differance. I get 19.5-20 back and forth to work, back country roads. I get around 18 if I stay under 75mph, 2000rpm, if I go over the 75/2000 mark I get 16-17. I think I hit 21mph, when I first got the truck and babied the throttle.
PS. I too am running with 3:55's, and 285/75's

Homestead

2000 rpm is your golden marker. I get awesome mileage if I stay under 2000 rpm. Anything over that and it just plummets. My sweetspot for best mileage is 1950 rpm. Not sure why the drastic change, but past that, I get OK mileage.

killfast1

I could understand if it stayed or got worse the faster you went but mine goes back up . Its like there is a big parachute that pops open when I hit 2000 and gets pulled back in when I hit 2150. I also have 3.55's and the stock size tires, I think 265/75. It just doesnt make sense that it would go back up after 2150rpm Other than that I love this truck.

I did the APPS reset also (initially not on purpose but it was a good time to do it as I left my headlights on and the batteries were dead). It seems to be more responsive and have some more power. I know it smokes more when I push the pedal through the floor. I love that smoke.


One day I will be able to afford some mods for it, then some more, and some more.

furious70

has this happened many times? If only once, maybe a bad tank of fuel on the middle test?

killfast1

No this is all the time. Have pretty much settled for this is how it runs but still would like to know why? I have learned to keep it below 69 or above 79. Even running A/C it doesnt seem to make a noticeable difference but the speed does.

DieselDaze

I know a lot of our trucks will suffer lower mpg after the 2000 rpm mark.
I do not believe Ive ever heard of someone getting better mileage higher in the rpm range though.

Thats an interesting one.

Rich

killfast1

My turbo consitantly produces the most boost at about 2150 RPM. I hear it start to while at that rpm level and it is really whining at 80MPH. Could this be from turbo lag? At 2150 or just above that, is where I have the most power also. That is why I am kind of thinking this (turbo lag). It also runs quieter at these higher rpms (not any drone from straight pipe). Just hate that it starts defueling around 2800 RPM.

My turbo seems slow to spool up unloaded. Not sure if its just me or what though.