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99 C1500, 5.7 fuel mileage

Discussion in 'Chevy C/K Truck Forum' started by 59diesel, Apr 23, 2012.

  1. 59diesel

    59diesel New Member

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    Just wondering if someone can gimme an idea of what mileage I should expect.. I have a 99 C1500, extended cab, auto, 5.7 Vortec with 118K total on it, all 100% original except for the tires, have gone to a 31-10.50-15.............recently I have done a complete tune up, cap, rotor, wires and plugs, along with pcv and fuel filter......I keep it very well maintained and it runs like a new one (and drives like a new one now with complete front susp rebuild).........One thing I CANNOT seem to find a timing tab...if it is there its where I cant see it........hook a timing gun to it, and the timing mark is dead on straight up on the damper.......if you move the distributor more than just a little bit, the "service engine soon" light comes on.........retard or advance, move it back and the light goes off............anyway, like I said, it runs great and the plugs look good, I average about 15-15.5 mpg on regular unleaded with kind of a mixed driving, highway/city.....it does show to have a rearend code of GU6, which I think should be a 3.42 ratio.............any thoughts on this mileage, or ideas on the timing tab ?
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  2. rileyjr16

    rileyjr16 New Member

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    I'm gonna go out on a limb and say about 14 highway/city

    ---------- Post added at 03:25 AM ---------- Previous post was at 03:24 AM ----------

    I put 265/75/15s on my 97 Cheyenne with a 4.3 and I got about 13 highway/city which I still regret doing.
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  3. revscott

    revscott New Member

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    I put 265/75/15s on my 97 Cheyenne with a 4.3 and I got about 13 highway/city which I still regret doing.[/QUOTE]

    I switched to the smaller 235/75 R15's, got a little better mileage, but dont like the look the tires look really small compared to the 265's. I want to switch back!
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  4. rileyjr16

    rileyjr16 New Member

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    I switched to the smaller 235/75 R15's, got a little better mileage, but dont like the look the tires look really small compared to the 265's. I want to switch back![/QUOTE]


    Go 265 but go with a smaller ratio if you want the width.
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  5. murdog94

    murdog94 New Member

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    Alright im gonna touch on the timing. do not mess with it. It is set by the computer and the only mechanical link is stabbing the dist. at #1 TDC. The rest has to be set by a shop or if you have the correct computer to do it. there is no timing tab.
    You are getting right in line what i would expect. on a long highway drive i would expect 18ish, and pure town about 13-14. So you are getting average milage.
    #5

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