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Thread: in town fuel economy
          
   
   

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  1. #1
    old guy 44 is offline CHR Member Visit my Photo Gallery
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    in town fuel economy

     



    I have been searching this and other forums regarding the in town mileage on my 03 GMC 4WD 5.3. My first thought was pulling the engine and recamming, possibly a bump in compression, smaller valve and port heads if they exist and whatever else I could think of at the time to trap cylinder pressure in the lower rpm range. I haven't found anyone yet that has tried a strictly mileage build on one of these and it just occurred to me that maybe I am trying to use a shotgun to kill a fly. The highway mileage is around 17-19 depending on speed. In town mileage however is deplorable. I have owned this thing for a little over a year and I doubt that it has ever seen the high side of 9 regardless of how I drive. Is this normal? This is the first LS engine I have ever had and do not know what to really expect from it. If this mileage is not normal is it possibly an engine management problem? I have plugged it into a scan tool and there are no codes, so either everything is operating within parameters or the ECM thinks that they are. The truck runs fine, has good throttle response and gives no indication of any problems. It just sucks fuel the way I used to drink beer in my 20's. If this mileage is normal the engine is coming out. If not does anyone have any suggestions where to start/

  2. #2
    DennyW is offline CHR Member Visit my Photo Gallery
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    323 V6's were not the best fuel types. 13-14 to 19 on highway. You say 4WD. That in itself will eat up fuel with that cubic inch engine. Just doesn't have the power. If it has to work harder, you have to feed it.
    Last edited by DennyW; 12-27-2016 at 09:26 PM.

  3. #3
    old guy 44 is offline CHR Member Visit my Photo Gallery
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    It is the 5.3 V8 not the V6. As for the 4WD it is 4WD not all wheel drive like most GMC's I have seen which means that in 2WD the front axle is disconnected and not turning the front differential like my 99 suburban did. Even at that the difference in city fuel economy between my 4WD and a 2WD suburban was only 2 to 3 mpg even turning the front differential constantly. So the net result of the 4WD is only that it is carrying the extra 300 to 400 pounds of equipment around, transfer case front diff and driveshaft etc. which is like throwing a small load of dirt in the bed and driving around. I would not expect a small payload in the bed of the truck to dramatically reduce fuel economy. That would be like putting two or three friends in your car and having the gas mileage drop dramatically, just not going to happen. The advertised mileage on the truck is 14 city and 18 highway. The factory ratings are determined with a professional driver generally downhill with a tail wind, or so it would seem. interestingly enough this truck exceeds the factory ratings on the highway but falls 5 to 6 mpg short around town which is why I would like to hear from someone with a similar truck and get some real mileage figures.

  4. #4
    DennyW is offline CHR Member Visit my Photo Gallery
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    My first suggestion would be to get the injection system professionally cleaned. At low speed, if they have any build up, this would effect the in town fuel mileage very much. And would not effect highway speeds. The slower in town, if the injectors are clean, gives you a finer fuel mist, and much easier to fire to get the most efficiency. I would also make sure the air filter is clean. Are the plugs older ? Plug gap also plays into it.

    ps: Does the oil smell gassy ? Are you using a good grade of oil ?
    Last edited by DennyW; 12-28-2016 at 10:53 AM.

  5. #5
    ted dehaan's Avatar
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    Have you checked your air filter
    I'LL KEEP MY PROPERTY, MY MONEY, MY FREEDOM, AND MY GUNS, AND YOU CAN KEEP THE CHANGE------ THE PROBLEM WITH LIBERALISM IS SOONER OR LATER YOU RUN OUT OF OTHER PEOPLES MONEY margaret thacher 1984

  6. #6
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    Something is wrong here-I have owned (or own) at least 7 of these Units (in either Yukon/Tahoe or Sierra Pickup) and, most of them before the 6 speed (I'll talk about those in a second)-

    The pre-2008 models were all 4 speed Autos, and the worst Gas mileage I've seen was in a Tahoe that had 4.11 Gears (it was a terror around Town-not so much on the Hiway)-the best was with a Sierra (lighter, equipped with 3.42 Gears), and it got 22 mpg on the Hiway, and about 14-15 in Town (by the way, the only full-size GMC's that are AWD are Denali's)-

    As far as the newer 6 speed models, they suck (as far as Gas!), especially if you live where I do (western US with lots of Mountains, Hills, and undulating terrain)-best mileage I have seen with the 6 Speed was 11 in Town and 16 Hiway (the eight speeds aren't any better)-

    First off, do you have 3.42/3.73 or 4.11's in it? This made the single biggest change that I've seen (I've owned them all), and where/what kind of driving do you do?

    I would agree that you have some kind of problem, as even with my '99-(first one-3.73 Gears), got about 20-21 Hiway, 12-13 in Town-do you tow a lot of loads? Are you getting this info from the Trip Computer or are you doing the math? Lots of variables here-

    I never had a single Injector problem, as a matter of fact one of my friends bought my '06 (it has over 350,000 on it now) and no Injector problems-

    I also noticed that Tires make a difference, and after trial and error I now only run Michelins (they can make up to a 2 mpg difference)-are you running the Stock size Tires (is it lifted)? I've put up to a 6" leveling/2" rear lift without issue-

    You need to find a driveability guy who knows these Trucks/SUV's and have him give it the once over-has it had a Tune-up?
    Last edited by 35WINDOW; 12-28-2016 at 01:17 PM.
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  7. #7
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    Alignment issues with quadrasteer-----------even if its aligned perfectly ( good road milage) any time you turn it any direction except straight ahed, you will hav terrific road drag because of weird geometry in that system to accomplish those turn radius---- and in town, you are never running very straight for very much of the time------

    tire types -------best at Micheln LTx----------

    Driving tip--watch all the dummies/crazys around you and DON'T drive like them-------
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  8. #8
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    Quote Originally Posted by old guy 44 View Post
    does anyone have any suggestions where to start?
    Trade trucks.

    .
    NTFDAY, DennyW and jerry clayton like this.
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  9. #9
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    Have you replaced the oxygen sensor on it lately? I've got some friends with these in hot rods and they started getting horrid mileage and another guy mentioned that dirty oxygen sensors will cause this. He said they still read but not accurately and it'll cause the computer to compensate and run it rich but not overly rich to flag for codes. They changed theirs and got back to good mileage again. Just a thought.
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    Ryan
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  10. #10
    40FordDeluxe's Avatar
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    Quote Originally Posted by jerry clayton View Post
    Alignment issues with quadrasteer-----------even if its aligned perfectly ( good road milage) any time you turn it any direction except straight ahed, you will hav terrific road drag because of weird geometry in that system to accomplish those turn radius---- and in town, you are never running very straight for very much of the time------

    tire types -------best at Micheln LTx----------

    Driving tip--watch all the dummies/crazys around you and DON'T drive like them-------
    Aren't these designed to lock out the rear steering function above 25mph so at high way speeds and as long as the alignment is correct, this shouldn't be an issue. I'm failing to see how the road drag will eat the tires here? It's a Dana 60 designed to be in the rear. The fronts sure don't have this issue. Any of these I've been around didn't wear tires any worse than a regular truck. Unless it had worn components like anything else.
    Ryan
    1940 Ford Deluxe Tudor 354 Hemi 46RH Electric Blue w/multi-color flames, Ford 9" Residing in multiple pieces
    1968 Corvette Coupe 5.9 Cummins Drag Car 11.43@130mph No stall leaving the line with 1250 rpm's and poor 2.2 60'
    1972 Chevy K30 Longhorn P-pumped 24v Compound Turbos 47RH Just another money pit
    1971 Camaro RS 5.3 BTR Stage 3 cam, SuperT10
    Tire Sizes

  11. #11
    old guy 44 is offline CHR Member Visit my Photo Gallery
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    I have submitted a detailed response twice now and it will not post. I am trying this just to see if it posts.

  12. #12
    old guy 44 is offline CHR Member Visit my Photo Gallery
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    OK that posted so we will try again.

    Gears, tires, modifications. As near as I can tell the truck is bone stock except for aftermarket wheels with 265/75/16 tires. I crawled under it and could not find a tag on either differential but the engine is not spinning up enough to have a gear set in the 4's.

    Driveability, I grew up in my dads repair shop and wrenched professionally for over 20 years and the truck has good throttle response, the engine is crisp and not laboring like something is wrong. I have not kept a detailed log of fuel usage however I used to have a second home in the mountains. It was a 230 mile round trip and if I went up and did not do much driving up there I would get home with slightly less than half a tank. If I put 30 to 40 miles on the truck up there I would need to stop for gas on the way home. My normal usage is Los Angeles traffic which if you know it no explanation is necessary if you don't no explanation is adequate. In that environment it will suck the tank dry and set the low fuel light in less than 200 miles, sometimes a lot less.

    Tune, It had new plugs and filters in it when I bought it, I am assuming that they are the correct ones because I found it at a dealer and in 20,000 miles of driving the economy has not changed. On the subject of tune what about different plugs like E3's they make a lot of claims but what is reality? Also what about one of the aftermarket tuners? If the thing had a carburetor and distributor I would be playing with re-jetting and re-curving the distributor but it is not so easy with electronics. I never thought about the O2 sensor, cheap enough to throw one at it and see what happens.

    Quadrasteer, I normally drive in 2WS because of an undiagnosed problem with the rear steering dropping out of 4WS into 2WS and not centering the rear steer. That is another thread.

    Denali, my truck is the only non denali quadrasteer I have seen. Do not know if it was ordered that way or not but it seems to be a one of or close to it.

  13. #13
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    Quote Originally Posted by old guy 44 View Post
    I have submitted a detailed response twice now and it will not post. I am trying this just to see if it posts.
    I learned a long time ago to copy my post before I hit send. That way, it isn't so much hassle to re-post. It's really sad, but this forum has turned into a second class operation.

    .
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  14. #14
    jerry clayton's Avatar
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    Well gas gauges aren't very acturet----------You need to fill it up, note odometer milage, drive it right around 100 mile fill up again and do calculation-repeat several times--- even go further-but keep a running record of miles driven and gallons used-I always only fill to auto shut off and don't top out ---------make it one of those graphie things and add notes to if long or short trips-------

    You may have as many as 4 O2 sensors--also chech coolant temp sensor and Inlet Air sensor

  15. #15
    DennyW is offline CHR Member Visit my Photo Gallery
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    Lots of good info.
    Let me explain what I meant when I said:
    At low speed, if they have any build up, this would effect the in town fuel mileage very much. And would not effect highway speeds. The slower in town, if the injectors are clean, gives you a finer fuel mist, and much easier to fire to get the most efficiency:
    The oxygen sensors can get coated, and they will not read correctly. But when you hit the high way, the exhaust temps rise, and burns it off.
    Along with checking the coolant sensor, you want to also make sure that the thermostat is actually opening at the right temp. If the thermostat, or the temp is to high, it goes lean, and the computer will richen the mix. Several things are tied together in the whole system. You must check and make sure all the things are working correctly. If TPS equipped, you have to also make sure the base idle settings (voltage) is correct at idle. If not, this changes things again in the mixture area, and timing. Just adding a little more info.

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