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  1. #1

    Default gas mileage = sad face :(

    If you look in my signature you could see many potential reasons for my poor gas mileage but I swear its the truth that doing every single one of those things has not changed anything in my mileage it has remained the same...
    i used to have just the throttle body spacer and cold air intake and flowmaster exhaust with stock tires no lift and still could never hit more than 15 mpg...
    even with gears, lift, tires i still have the exact same mileage which usually varies from 13 to 15 mpg, this is a V6 btw...
    my last 2 tanks however have been shockingly awful... ive been about 11.5-12 mpg and i dont know why!
    i just replaced my fuel filter, i have recently replaced plugs, wires, cap, rotor, oil, oil filter (fully synthetic for years now), sprayed my throttle body, cleaned my k&n filter....
    and i still cannot understand why my gas mileage is so poor i also recently seafoamed my gas tank and, a few times a year i am normally throwing in 44K (dads pick)
    But i have noticed over the last few months a minimal (noticeable to me) loss in power overtime and i havent seemed to gain it back yet...
    I really am going crazy with a 26 gallon tank that i have to refill after 320 miles.... do the math
    does anyone have suggestion/help/comments for me?
    I am wayyy past my high school gunnin the gas years and hardly ever beat the pedal unless necessary...
    but i am fed up with this mileage.
    2000 Chevrolet Silverado

    4.3L V6, 4L60E, 2WD, Single Cab
    Airaid CAI
    Poweraid TB Spacer
    Flowmaster 10-series exhaust (dumped)
    Edge CS insight monitor
    4.10 gears
    Limited-slip differential
    LS-1 Dual Electric fans
    Corvette tranny servo swap

    Head Unit: Alpine
    Speakers: Alpine SPR-60C 6.5" component set, 4X6 Infinity Kappas
    Subs: 2-12" Kicker CVT's
    Amps: Alpine-M1000 (subs), Alpine MRX-F65 (Speakers)

    305/70R16 NITTO Terra Grapplers
    16" PROCOMP 7089's
    2" leveling kit
    3" Fabtech Spindle Lift Kit
    Front/Rear-Bilstein 5100 shocks

    35W HID Low Beams
    RECON LED smoked roof cab lights
    HELLA LED taillights and 3rd brakelight
    HELLA FF-75 Aux. Reverse Lamps
    RIGID dually D2, flush mount, wide beam
    Hawk HPS Brake pads
    Russell braided steel brake lines
    Powerstop-red powdercoated brake calipers
    Powerslot Cryo brake rotors
    EGR in-channel window visors

  2. #2


    I'll probably upset a few people with this post but IMO the reason for your poor fuel mileage is the 4.3.
    It's never been a great fuel mileage engine, even in the S series trucks it didnt get much better than what your seeing.
    I really think deleting the two cylinders killed the performance of that engine and I've always felt it was underpowered for a full size truck which causes it to work harder and consume more fuel.
    As to why your suddenly experiencing even worse performance and mileage? Good question it appears youve done everything to ensure the maintenance is up to date.
    Have you checked the compression lately? Maybe the engine's getting ready for a rebuild/replacement.

  3. #3


    not upsetting at all i have heard from multiple people and assuming basic physics i agree that smaller engine = more work especially for a full size truck.
    i can see how a v8 would not have to work as hard to get the momentum going etc.
    but why would this truck be rated 16 city 20 highway if it could never reach it especially if it was stock and had intake exhaust and tb spacer??? (all mpg/power boosters)
    and i have heard alot about checking compression? where can i do that though i would not want to do it myself is it cheap to get done? and where at?

  4. #4


    The reason the trucks rated at those figures is because GM was under a mandate to produce fuel mileage numbers in a certain categorie.
    After a lot of work they got a truck on a test track under perfect conditions to perform those numbers.
    So they got their CAFE rating and sold trucks and everyone was happy.
    Except the purchasers of those trucks that never got them to perform nearly as good as GM's claims. But to be fair every car manufacturer does this to meet their mandated numbers.
    Compression testing is easily done in your driveway, most AutoZones will rent or loan a compression tester.
    You'll need to get the appropriate section of the maintenance manual for your particular truck/engine to compare your readings and familiarize yourself with the safety precautions.
    The short explanation of the task is remove the first spark plug, put in the compression testor adaptor, neutralize all the other spark plugs so the engine wont actually start, have someone turn the engine over while you record the readings on the compression testor gauge, then proceed to the next cylinder, repeat the proceedure until you've got a reading for every cylinder, compare the readings you have with the manual and see if you have any exceptionally low cylinders.

  5. #5

    Enkeiavalanche's Avatar
    Join Date
    Apr 2010
    Piermont,NY, back in Northern NJ now, But may be in IL soon....


    How do you have the programer tuned? How do you drive? Do you use E-85 at all? Do you coast down hills? Have you checked out the rolling Resistance on those tires? How long ago did you put the bigger tires on?
    08 Z71 Avalanche Mods to date: K&N CAI,Hellwig Swaybars and End Links, Corsa Sport Exhaust, Superchips Programer,IPCW LOF & 3rd brake light and tails, AMI Gas door,Show Hooks and Door locks, Enkei Wheels, with Pirelli tires, StreetScene Bowties, Grant Steering wheel,Muth signal mirrors,SSBC Big Brake kit,Huskyliner Mug gards,Floor mats and Hood shield, McGard Lug nuts and locks, Bedrug, Cervini's Ram Air hood,35watt HID Fog lights, Sylvania bulbs all around ZXE's Highs and Lows, WhiteNight Back up lights,Sirius and HD Radio, SnugTop sitting on deck now Got a Softopper on now,Tempress Boat Hatches.... New Bilstein shocks are on... New Mods coming soon..... X

  6. #6

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    Like Avalanche says- if your station suddenly went from pure gasoline to Gasohol- up to 15% alcohol- your mpg could drop 1-2 mpg easily.
    Check the pump at the station -see what it says.
    Like TB implies- the 5.3 is hard to beat-the 4.3 and 4.8 usually can do no better than match it- and usually fall a bit short of the 5.3 in respect to mpg.
    PS But the sudden drop makes me think ethanol in gas- or you switched stations to one that has ethanol.
    1998 suburban-
    1/2 ton

    199500 miles

  7. #7


    Look for a gas station that sells non-ethanol. After about two tank fulls your mileage will pick up. I gained back 2mpg and mrs. silveradotrailblazer picked up 4mpg's on the highway.

    2005 Chevy Silverado Z71 Crew Cab
    6" Skyjacker lift w/Edlebrock dual front remote resoviour shocks, single rear remote. Rancho skid-plate.
    17" x 9" M/T Classic Lock Wheels, 35" BFG A/T or M/T tires
    4.10 PercisionGears w/factory locker, T/A Performance rear-end cover
    Banks CAI intake, ported throttlebody, JBA coated headers, over-sized Magnaflow cats, Magnaflow cat back exhaust, Diablo tuned
    B&M aluminum deep transmission pan
    Warn brush guard w/Warn 9.5 XP winch, PIAA bulbs, Line-X bedliner, AWS Black tool chest, Extang tonneau cover
    Weather Tech floor mats
    Cover-Craft seat covers
    Dash mat cover
    Formula One window tint
    One black Lab in rear seat.

  8. #8


    I agree with everyone here - the 4.3 is a bit of a pig because it just doesnt have the power to move a vehicle that heavy. Even in 2011, it still only has 195 horsepower and 260 ft.lbs of torque. I also agree that its possible that a change in the gas where you fuel up could cause your recent MPG drop. Also, like enkei said, you might be able to get 1-2 back just by adjusting your programmer a bit, depending on how it is set now.

    One more suggestion I have is to clean your Mass Airflow sensor, especially since you have a K&N intake. Over time, the mass airflow sensor can get dirty and cause poor performance and fuel economy. The oil on K&N filters also has a tendency to coat the mass airflow sensor and cause problems with it - particularly if you might have over-oiled it at some point. To clean the sensor, you just need to pick up some mass airflow cleaner (safest to get this because other cleaners could damage the sensor) and give it a good spray. let it dry and then reinstall it.

    2008 FORD F350. My new all-around truck.
    2001 Silverado Reg. Cab Not-So-Base -- SOLD
    2003 Avalanche Z71. No Cladding. Check out my Mod thread. - Crashed. Will be rebuilt soon.
    1974 Triumph Spitfire 1500 - Work in Progress
    2003 Sierra 3500 Duramax. The Newer, Better Work Truck -- FOR SALE

  9. #9


    Big tires and lift kit are hurting your economy.

    Quote Originally Posted by tbplus10 View Post
    The short explanation of the task is remove the first spark plug, put in the compression testor adaptor, neutralize all the other spark plugs so the engine wont actually start, have someone turn the engine over while you record the readings on the compression testor gauge, then proceed to the next cylinder, repeat the proceedure until you've got a reading for every cylinder, compare the readings you have with the manual and see if you have any exceptionally low cylinders.
    When doing a compression test -

    Remove all spark plugs. Hold the butterfly wide open. Pull the ECM fuse. Then do the test as described above. You need the butterfly open to get plenty of air in the cylinders. You also reduce load on the starter/battery because you're not pulling any vacuum. That's also why you pull all the plugs first.
    When you hear hoofbeats, look for horses not zebras.

  10. #10


    as far as tuning my hypertech programmer there isnt much to do its only actual "tune" function is to choose regular or premium fuel, then theres other little things like shifting and top speed limiter etc...
    theres not many hills in corpus christi, and as far as rolling resistance im not sure, but my tires have a T speed rating so i would assume there wouldnt be too much resistance for an AT tire to have that high of a speed capability and i have had these tires since december 2008

    ill need to look over that ethanol deal yall are talking about and definitely should check out my mass airflow sensor

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