hey guys, on the way to Huntsville, i got about 14.9 avg MPG going 75. WTF? i know that one of my after-cat O2 sensors is out, but could that really make that big of a difference? my truck used to get 18-19 in the hills around alex city.

 

Cold weather makes a big difference...

 

historically my gas mileage gets better in the cold

 

Winter gas gets less Mileage. and going 75 won't help either. Try 65-70

 

I just did a 250 mile road trip. Tupelo to Birmingham and back. 15 mpg. So don't feel bad.

 

Averaged about 21 on the last road trip traveling about between 70-75 with mods in signature. Drove from NW Arkansas down to Southern Arkansas to visit family. Trip down the mountain netted 22.3mpg (as close to 70 as possible), trip back up ran about 19.5 mpg (closer to 75 most the time)including a little play time with a noisey import. Both trips were started with engine warm and no more than 3 miles getting out of town and up to hwy speeds. First tank was filled from station that advertises no ethenol. Second fill up for trip home might have been at a valero (cant remember).

I'm really happy with my setup. In town millage is a whole different story running between 12 - 13, unlocked tc loves the gas.

Last truck was a '99 5.3 rcsb with a westers tune, intake, exhaust, headers, tb tc and average 17.5 @ 80, 19+ @ 70-75.

Don't think your rear o2's have anything to do with it. I'd get with a good tuner, any of the sponsors can help. I'm running Black Bear on current truck..

 

update*
what scares me is that the first time that i came up here, i ran 85 and got about 18 mpg, so i'm clueless as to what's going on.
just filled up and the mileage has gotten worse. around town i'm getting about 9.9 mpg. i'm starting to think that there is something severely wrong. any ideas?

 

it's the ethanol in the gas. pretty much all gas now is at least E10

 

Original front O2 sensors? Bad O2s have made my mileage go to crap before, but that was on a 94 sierra.

 

why would it scare you?