Air/Fuel ratio for differant altitudes??

Discussion in 'Performance & Fuel' started by BlueLT1500, Jan 18, 2008.

  1. BlueLT1500

    BlueLT1500 Rockstar

    hopefully this hasn't all ready been answered somewhere else and if it has pointing me in the right direction would be a great help.

    I recently bought a used 07 silverado 1500 ext cab 4.8l with 16k miles on it in vegas. the week i was there driving it around i got about 17-18 mpg in town and as i drove it from vegas to cali i got ~21mpg. my problem is that after leaving cali to head home to el paso every fill up from there my mileage dropped. first fill up was 19, second 18, third 17 and has now settled right at the 17 mark on the highway and i am down to about 14-15 in town. I am wondering if the fuel management system in the computer hasnt compinsated for the altitude changes and isnt running quiet right. and if this is the case does any one know how to fix this. other wise does anyone have any ideas on what the problem might be. i did drive with the tailgate down the whole trip. also when i got to el paso i installed the K&N drop in filter.

    Any help on this would be great, Thanx
  2. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    The fuel management system in your vehicle adjusts to altitude very, very quickly-less than a second.I have heard There is another sort of system in some vehicles that does adj to your driving style,and this is said to take several days/rides(I have my doubts about how much mpg difference this makes-I have heard of it in reference to some Hondas).
    Bottom line,I suspect your mpg difference might be altitude or the prevailing winds on your trip to California(Cali?).I drive from New Orleans to Flagstaff AZ fairly frequently. I get better mpg-much better-once I get to 3000-4000 feet.There is much less air resistance at altitude,so you get better mpg.In the old days-with carbs-a sea level vehicle would get HORRIBLE mpg if it went to altitude-no power,and terrible mpg.With EFI/O2 sensors,mass air sensors the mpg actually improves at altitude.
    I'm not sure about the prevailing winds-you more or less went East to West,then west to East to El Paso.If the winds were at your back going to CA(good mpg),then they would be in your face going home.
    I have been thru El Paso several times(I-10)- about 100 miles E of El Paso, on I-10-there is a big wind farm-the wind blows hard out there!
    14-15 mpg is better than average for city driving.17 mpg is about what you would expect at 70 mph-if you are doing 60 mph,then you should get better than 17 mpg. A few years back,the K&N filters were "killing" the mass air sensors because they were being over oiled,and the oil was doing in the sensor.I don't think that an air filter will improve part throttle fuel economy(assuming the old filter wasn't gunked up), but many,many folks disagree with me on that point.
  3. BlueLT1500

    BlueLT1500 Rockstar

    thanx Charlie, yeah i was really wondering about the wind and i was pretty sure the air/fuel was suppose to adjust on the fly but it just really baffled me that the differences were so large. as i was reading along yesterday i did find a post that said something about driving habits and the transmission learning how to adjust to my driving style so maybe this is it. We are going to do a test in the next couple gonna let the feather footed wife drive us to some wineries in NM and see how different the mileage is then :lol: and then we are going to be driving back to vegas in March for my brothers wedding so we will see how that goes as well..we will be getting the tonneau in a couple weeks also, so i have heard that the y do and dont help so i guess we will see on that one as well lol...thanx again for your input

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