horrible mpg

Discussion in 'General Chevy & GM Tech Questions' started by Silverado1500, May 6, 2010.

  1. Silverado1500

    Silverado1500 Rockstar 100 Posts

    i have a 2000 1500 4x4 5.3 silverado and i am getting 9-11mpg city and highway. i have a 26gal tank and get around 250-310 miles per tank.

    i have no idea why i have such bad mpg.

    i am running 305/70/16 with stock gearing. custom exhaust, CAI, tuneup done in january(fuel filter, CAI install, plugs, wires, oil, oil filter, seafoamed through gas tank and vacuum line.) just changed the TPS.

    and another thing which i do not know if this is a factor in mpg but my gas gauge doesnt seem to work...the low fuel light is always on when starting and turns off and shows amount of gas after about 5 mins of driving. and when i fill my tank it shows empty even when driving.

    ive been stumped on this for months and cannot find the solution.
     
  2. Greg84

    Greg84 Rockstar 100 Posts

    The big tires kill mileage. Mine dropped from 16-17 with stock tires to 12-13mpg with 285/70/17's, your tires are even larger (those must be close to a 35" tire!), plus if you have any lift kit on it that isn't helping it either.
     
  3. Silverado1500

    Silverado1500 Rockstar 100 Posts

    its about a 33 inch tire. 32.8 to be exact
     
  4. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Hey Silverado have you tried a programmer to get the shift points back to where they need to be also to get your speedo back to the correct reading. Because running that much taller of a tire makes your speedo read slower than you are going and then your odo actually shows less miles that you have actually gone.. Also changing the pump module as discussed in other threads should fix your gas guage.. and that will help also so you know better to how far youve gone and how much fuel you have left.
     
  5. Loggerhead Mike

    Loggerhead Mike Rockstar 100 Posts

    have the ethanol in your fuel tested. biggest mph killer

    get a good injector/carbon clean, not the stuff in the cans at the parts store

    you more than likely have some broken wire strands in the fuel sender or high resistance in the signal circuit
     
  6. Silverado1500

    Silverado1500 Rockstar 100 Posts

    alright. thanks guys
     
  7. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Have you corrected your MPG for tire height?
    Your new tires must be at least 1.5" taller than the old ones.

    If the new tires are say 3" taller than stock your actual mpg is 10mpg X 33/30= 11 mpg
    Your actual distance traveled would be 10% more also.

    If the difference in height is more like 1.5" then it is .5mpg off.

    I'm guessing your original tires were 265/70 16?

    So these 305/70 16 are two times (305-265) times .7=54mm or 2.2" taller or 6.6% taller.
    Your real mpg is about .66 mpg more.
    Your real distance traveled is about 6% farther than your odometer says.

    If this was already discussed-sorry-I should have read more closely.

    10-11 mpg isn't really bad for a 4x4 GM 5.3 in pure city driving. Now 11 mpg is pretty bad for hy driving-With stock profile "street type" no big mud lugs tires you should get 15 mpg or so.

    Bigger wider tires do decrease real mpg-especially if they are mud type off road type tires.They are wider-more wind resistance-and usually have higher rolling resistance.
     
    Last edited: May 18, 2010
  8. Silverado1500

    Silverado1500 Rockstar 100 Posts

    wow thats some great info right there. thanks man!
     

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