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Discussion Starter #1
I promise that this isn't another thread where someone wants to know why they're truck with 40s and a 12in lift has bad fuel mileage.

Truck is a 2013 4.6L Double Cab Short Bed 4x4 and approximately 18k miles. No recent mods that would cause a sudden drop in MPGs but for informations sake the truck has 275/65r18 Goodyear AT tires and a 2in level kit.

I hardly ever use 4wd, and usually only let it warm up for 5-10 minutes before driving. 80% of my driving is at 50-60mph. 10% is at 30-40mph, the other 5% is 75-80 on the highway. I'm not a super aggressive driver but I don't like going slow either.

Typically my truck gets around 17-18mpgs. I always use 87 gas and winter gas has been around for a few months now and was getting around 14-15mpg but on my last two or three fill-ups my fuel mileage has been horrendous. Hand calculated I'm getting 11-12 mpg. I went 192 miles on just under 15 gallons of gas on my last tank. The first bad mpg tank I chalked up to maybe a bad tank of gas but this is now my 3rd tank of bad mpg from different stations.

Now I know it's a truck not a Prius, I'm more concerned that it's been such a sudden drop that something may be wrong with my truck and that could be why the mpg has dropped seemingly out of nowhere.

Any ideas? Truck is coming up on 20k mile maintenance and will ask about it there but would like to give them so ideas to check out along with my squeaky brakes.

Thanks in advance for your help.
 

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With the cold temps have you been idling more than usual to get it warm? Same gas station?

I'm from upstate NY and my vehicles ran better when I put Sunoco fuel in it, don't know why but it seemed to run the best.

I have never used any of the Murphy or cheap fuel stations only brand name.
 

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Discussion Starter #3
Thanks for the reply. Trucks been doing the same 5-10 minute warm up since early-mid December when it first started getting real cold. It only warms up in the morning too, I don't let it idle when I leave work for lunch, leave class, or leave going too or from job #2 .

I usually use Cumberland Farms or Hess gas, sometimes Mobile but no real Sunoco stations around here.
 

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Are you still using the same station and brand of fuel. They could have moisture in the tanks or just a bad batch of fuel or worn out fuel filters. If so, I would try a different high volume station and maybe even another brand.

JMO but a 5 to 10 minute warm up seems quite a bit. I do a minute to minute & half idle to get the oil circulated and the RPM's drop down.
 

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Discussion Starter #5
I have about three different stations I use, one close to work, one close to home and one on the way home from job number 2. I use the one close to home most frequently but have used different stations these last few tanks trying to figure out why the MPGs have dropped.

I'll try a shorter warm up time on the next couple tanks.
 

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My mpg suck when its super cold too...any truck, any brand. Seems to run richer and all the moving parts take for ever to get warmed up to get ahead the mpg curve on the ride. This morning it was -23 here..
 

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Is your truck a flex fuel? If so, the alcohol density may be acting up.

I would suggest removing the negative battery cable for some time and seeing if that makes a difference.

Completely hypothetical. I feel like my MPG went down quite a bit, and I just ignored it. I had my truck in for some service (shit issue I caused) and that required that the logical system be disconnected for a while. Now that I have the truck back, the mileage has restored back up to the upper teens and it seems to be more responsive. I might be full of shit though. Lol.
 

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Discussion Starter #8
I'll have to try the battery thing although my truck isn't a flex fuel.

My commutes are typically 10-30 minutes, not sure how long it would take to warm up enough to get to decent mpg area though.
 

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Even with no engine light on (right?), it might not bad idea to have it scanned. I would try the dealer or a good local shop, the scanners they use are usually way better then the parts stores "Free Scan"

A good local shop won't charge you more then a few bucks if not free....
 

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winter gas. Try the battery reset. Isn't there a fuse to pull also? Can't remember. Might be an entirely different vehicle though. Number 5 fuse??
 

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Sorry guys I'm new here and want to be kind. Please stop with the battery reset and look into placebo. You do not need to look into an expensive scan tool, if you truly are concerned about fuel mileage then get any obd2 scan tool that will also give you data. Not just codes. Once you get your data look at your fuel trim, as long as your long term is within plus or minus 5 percent then you need to come to the realization that it is you/traffic. If you want to save yourself the trouble then just wait for the check engine light to come on. I promise you if you're engine truly is requesting that much additional fuel without the request of the user the check engine light will come on.
 

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I agree about trying the battery pull/ECU reset. Have you checked the tire pressure? Cold temps will really drop the tires down.

It's worth looking at your air filter/air box. Seems crazy but I'd make sure the air inlet to the box is free and clear and that the air filter doesn't need to be cleaned/replaced.

You may also run some injector cleaner through the gas. At 18k it shouldn't be a dramatic difference but I'm bought in to using this stuff at a regular frequency as good maintenance.

If you still feel like it's a problem after all of this stuff you might clean your MAF.
 

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My personal theory (for what it's worth)...

The ECU adjusts. If he had bad gas the ECU could have tried to compensate. In time ECU values would return to normal performance. Resetting the ECU forces it to start over and start learning right away.
 

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I totally get why that sounds good, but it just isn't true. For one thing you're not resetting anything and for another your computer is adapting immediately and logging that immediate information for the long term. This theory kind of made sense a long time ago, but it's just not true today. After a battery is disconnected the vehicle still remembers its long term fuel trims and gives the engine that amount of fuel as soon as it enters closed loop. The only thing that may reset is your instrument clusters mpg which after your reset the battery for what you might think is going to give better mph is most likely going to cause you to drive lighter because we all like to prove our own theory/hopes. Anyhow... it's doing nothing.

I promise everyone reading this that the EPA and every other acronym cares way more about what your fuel standards are than you do. Engineers would sell their mothers to get you an extra mpg. If disconnecting your battery even gave you a chance at something beneficial it would be required at every service. In fact they'd make you come in every 250 miles for a mpg service and we'd charge you for it.

I promise you, 99.9 percent of the time, unless you just got done off roading and sucked up a bunch of mud in your air filter the reason for your fuel economy decline is you getting used to driving the truck and enjoying yourself more. Even mud in the a/f would end up setting the check engine light as it would be running rich. If there truly is a problem your fuel trims will withing a relatively short time go out of their parameters and give you a check engine light.

Sorry for the rant, but I just wish most people could see how well modern automotive engines monitor their own efficiency in real time and learned time.

Moral of the story... relax. It's you... and maybe.... and this is a super maybe... the fuel mixtures at that particular time of the year... but that's a super maybe. Reality is, it's most likely you. And if you don't believe me... reset your mpg counter, drive like a grandma, watch mpg rise. Don't use the well nobody drives like that in real life argument... if there really was a problem grandma wouldn't be able to trick a failure with driving habits.

I know there's a lot of people smarter than me on here, so if I'm wrong about anything here please correct me so I can find myself a little more educated. Again I'm new here and hope I'm not overstepping.

Edit: Just understood a bit more of what you were saying.... had it had bad gas your short term would have compensated and your long term would have moved. However, once you got a good tank your short term would have adjusted your long term. Regardless a battery pull is doing nothing to help this process along.
 

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a little more info here... I have to say I'm not an ECU engineer or a mechanic just a guy who enjoys learning about the Tundra and doing things myself. If I've learned something from reading on the forums I'm happy to pass it along to the next guy.

I should add, I'm not suggesting a quick battery disconnect which would just clear the EVIC and your radio presets :( An ECU reset usually needs the battery disconnected for 30-45 minutes. From what I understand, after an ECU reset it throws away the old values and start learning fresh. Why could this be helpful?

If we think he might have had bad gas it could have resulted in an engine knock. From what I understand the ECU will retard the timing and it'll be hard for the ECU to trust an advance in timing. If the bad gas is gone, start over and start averaging new values cleanly.

The ECU is always learning but sometimes there is an advantage to starting over. From what I've read in the forums after an ECU reset, the ECU learns aggressively in the first 250 miles. All instructions for air intakes, throttle body spacers, after market MAFs all say to reset the ECU.

I'll add my own crazy theory, ever restart a pc, or power off your phone, unplug your digital television, or the forums suggest that even in our trucks you have to reset the stereo by forcing it to power off. It's just something that doesn't hurt, one thing to eliminate and rule out and it doesn't cost money. You'd feel silly to get charged for an ECU reset.

All that said and I tend to agree the most likely cause is the right foot or the weather.
 

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To the op, when you say the last three fill ups have been low mpg, how many total miles are we talking about? And how long a time period?
 

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It's been darn cold lately. I think that's the issue. Last winter I eeked by at I think 17mpg, something like that. Right now my Scanguage is indicating 15. Probably because every start has been at 10F or colder. Takes a lot of gas to start at those temps I guess; and then if you drive on a super cold motor it still takes a fair amount of gas. Not only that, but the diffs are stupid cold too. Takes a while for those to warm up and get the oil thin.

You could change the diff oil and check tire pressure (tires supposedly lose a psi per 10F, so if you last aired up in 80F weather they could be quite low). But my guess is that it'll go back to normal once this cold snap is over with.
 

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Discussion Starter #20
Hey gents thanks for the info, tried gas from a 4th station and combined with slightly warmer temps it has been just alittle better. Driving habits have been the same since day 1 and this is my second winter with the truck and I don't remember it being this bad last year but it has also been much colder this year. I'm going to just throw it up to the weather and mention it when it goes in for its 20k mile service in a couple weeks.

Thanks for your help!
 
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