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Thread: Aggravating Fuel Economy Problem

  1. #1
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    Default Aggravating Fuel Economy Problem

    I own a 2004 Silverado SS 6.0L. When i first got my truck in 2011 it was getting about 16.3L/100km & over the years since it has raised to 17.3L/100km not bad & nothing i really worried about over 7 years. This past November I was out hunting for a month hauling my quad in the bed of my truck & idling for long periods of time daily my fuel economy displayed in my truck was 17.3L/100km it has been that exactly for any recent memory. A month or two before i replaced my water pump because it was leaking so that's pretty much brand new. So hunting season ended and i was back to regular driving still 17.3L/100km. I dont really pay attention to it just when i see it scanning thru settings & resetting my personal trip mileage.

    My tensioner pulley & idler pulley were making noise so i ordered a kit to replace them. I replaced the tensioner & tensioner pulley, idler pulley & serpentine belt. Randomly looked at my fuel economy a random day after doing it and noticed i jumped to 18.5L/100km so i was like wtf don't 100% know if it it jumped before or after the work. Prior to installing those items i made sure they were exact sizes and direct replacements, all parts ordered off rock auto & i buy the premium parts. The old pulleys when taken off i could spin with my hand & would do like 30+ revolutions before stopping. The new bearings would not free wheel like that when finger spun they would spin maybe 1 or so revolutions. So in my head i was like there is no way the new bearings would cause that much drag on the engine making the fuel economy go down. So i thought maybe the tensioner itself so i put the new pulley on the old tensioner & reinstalled it. If i remember correctly there was a slight change for the better but not much can't remember exactly. A few fill ups go by & still getting the same economy 18.5-18.9.

    So next i decided to change the plugs & wires since they had 100,000+ km on them. Bought iridium AC-Delco plugs with the Premium AC-Delco wires to go with them. Change them, no change in fuel economy still around the same as before. Noticed my fan clutch bearing was making noise so i changed the fan clutch, while i did that i cleaned the MAF & also took my throttle body off and cleaned it and it was pretty dirty. Roughly a fill up goes by still no fucking change in my economy sitting at about 18.9L/100km steadily. After doing all this especially my new plugs my throttle response has been night & day difference but hasn't done shit to my economy. Went to my lake this past weekend with my quad & my economy went up to 19.1L. Getting 10/10 aggravated now. Get home un-load go fill up goes does to 18.9-19.0L these last 2 fill ups ive also been running injector cleaner in my fuel tank.

    All this time my check engine light hasn't come on, the ODB scanner i have doesn't show any codes or pending codes. I don't have a rough idle. After changing my plugs i did a kinda mini test on my coils, while the engine was running i unplugged then plugged back in each coil when i unplugged each one there was a change in engine idle it would go rough as in being a miss fire but when i plugged them back in it would go back to a smooth idle. I didn't fully test anything else with my coils because my throttle response is instant and there's no rough idle & I'm not too aware on how to do a full test on each one.

    I'm completely dumb founded on what it could be when it comes to doing a "tune-up" i think I've went above & beyond especially when 3 months ago i was at 17.3L/100km with none of this shit done except the water pump. Like what could it be a plugged cat? Bad O2 sensors? but that should throw a check engine light. Bad coils? but doesn't seem like they're bad. The serpentine belt was pretty much identical in length. Is new bearings in the pulley's causing drag which i think isn't the case just a thought i had. It's been about 2 fill ups of gas since all work was completed. I also don't slam on the gas, i drive pretty steady. When i do work i torque everything to factory specs, double, triple check everything.

    Any suggestions on what i could check or what it could be? I want to take it to a mechanic but i don't want him to diagnose it for 180$ then say nothing came up or whatever. Obviously as a last resort that's what id try. Maybe their injector cleaner service they offer, i really don't know.

  2. #2
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    Well, for one, you can't trust the calculated mpg indicator. It means nothing. Hand calc or dont worry about it.

    Two, if your highway driving/city driving split has changed, it will have drastic affects on your mpg.

    Three, are you sure this isn't just you randomly paying attention in winter time? Mpg will go down minimum 10% in the winter.

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    Quote Originally Posted by HiTempguy View Post
    Well, for one, you can't trust the calculated mpg indicator. It means nothing. Hand calc or dont worry about it.

    Two, if your highway driving/city driving split has changed, it will have drastic affects on your mpg.

    Three, are you sure this isn't just you randomly paying attention in winter time? Mpg will go down minimum 10% in the winter.
    All good advice. I don't think it's a full 10% drop in winter, but it's definitely a drop due to the extra butane that's blended in "as a favor" to call it #WinterGas.

    The "favour" is to the refineries because they have eff all market for their butane.
    Last edited by JugZ; March 16th, 2018 at 06:00 AM.

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    Well in winter in November i was getting 17.3/L/100km hauling 800lbs of gear and idling lots along with driving. I usually glance at it everytime i fill up and in the 7 years i've owned it I have never seen it above 17.3 regardless of season or driving habits. My highway / city driving stay pretty constant & if they have changed over the years it still hasn't been above 17.3. But yeah good idea i will keep track of the mileage manually & see how it changes over the next 5 fill ups & compare it to what the computer says.

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    Honestly seems pretty normal to me, dude. Your truck went from 17L/100km to 19L/100km because it's winter. /thread

    My truck goes from 13.5L/100km to 17L/100km in the winter time. I've owned the truck for 5 years and it does the same thing every winter.

    I'm back down to 15L/100km now that the weather is starting to get a little nicer. And by the time we're in the plus temps, I'll be back down to 13L/100km.

    I think you see a 2L/100km jump simply due to the winter gas and extremely cold temperatures. Colder air is denser, more air in the engine means more fuel to compensate and keep AFR's the same. Science bro.

    I see nearly 4L/100km jump because of the shitty gas, the colder air, and because I drive around all winter in 4x4, where your truck is AWD, and your baseline mileage is already worse. Plus the age of the vehicle, etc, etc, etc.
    Quote Originally Posted by LOLJDM View Post
    Rob with an awesome post as always.

  6. #6
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    Quote Originally Posted by JugZ View Post
    All good advice. I don't think it's a full 10% drop in winter, but it's definitely a drop due to the extra butane that's blended in "as a favor" to call it #WinterGas.

    The "favour" is to the refineries because they have eff all market for their butane.
    Guess it depends what vehicle you drive.

    Probably not going to notice much difference on a tiny little Honda that gets excellent mileage all the time, or a big jacked up truck that gets horrible mileage all the time.

    He's losing 12% fuel economy in the winter. I'm losing 25% fuel economy in the winter.
    Quote Originally Posted by LOLJDM View Post
    Rob with an awesome post as always.

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    I don't see any mention of an air filter, also MAF could be getting dirty. O2 sensors could also start to wear out, which makes engine run richer, it will only set an error code if a sensor fails, not when they send incorrect readings in their normal parameter range. You have an 04, so your useless park brakes could be dragging too, could be anything.

    Winter fuel does reduce mileage, along with cold temps, and its been cold this year.
    1993 B2200, S4 13B Swapped, 5-speed, otherwise stock

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    Don't forget the extra rolling resistance due to road conditions there is also and potential loss of traction in stop and go traffic, then you can add on how people like to warm their vehicles up.

    Couple weeks ago went to Saskatoon and back worst milage ever reported by the dash computer 16.5L/100km on the way back weather was nicer and there was very little wind and I was closer to 15L/100km without resetting it so the trip out was still effecting the numbers.
    Model View Caffeine

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    im in the same boat with a 2002 Supercharged F150. in the city im down to like 9 mpg. but on the highway i get a constant 15mpg.

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