My GMC sierra is getting horrible gas mileage and I did a full tuneup is there any other things it could be?
I have a 2003 Gmc sierra its the 5.3 liter. I bought it last year last time i checked it’s mpg it was getting 16 mpg while pulling a trailer. Now a year later i noticed I’m filing up more so i went and did a tune up, things changed fuel filter, oil, oil filter, spark plugs, spark plug wires, air filter, added fuel injector cleaner. I did this with my friend at his shop he owns and he didn’t notice anything else that needed to be changed. Well now I have been driving really thinking about conserving gas and just checked I’m getting 11.68 mpg. Is there something we are missing that could possibly be causing it to be this low. its a full stock gmc nothing modded not lifted no weight added and no codes or lights.
Thanks
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Filed under Gas Conservation FAQ by on Apr 25th, 2011. Comment. 
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Comments on My GMC sierra is getting horrible gas mileage and I did a full tuneup is there any other things it could be?
5.3 liter seems to about cover it.
Maybe you didn’t put in decent spark plugs and that made it worse. Did you use OEM plugs and wires? Could be the problem. How’s tire pressure? How is the car warming up? Does it get at normal op pretty fast or take awhile? Coolant level?
You should try some injector cleaner or take off the hose going the the carb and use some carb cleaner…..Steve
Ask your friend if he ran your VIN vs GM database of Advisories, Alerts, Memos, Notifications, Recalls, Service Campaigns, TSB’s [tech service bulletins], etc, etc.
I doubt he did, bc w/ most manufacturers that database is proprietary, ie, only GM has it.
Since 03, could be many of em.
Have GM run your VIN.
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“…independent mechanics complain they lack the proprietary tools and data to service many late-model cars…” some 2004 models and earlier.
They’r seeking a “Right to Repair” law allowing them access to manufacturers’ databases.
Wall St Journal, Feb, 2011.
. .
http://online.wsj.com/article/SB10001424052748703555804576102272750344178.html?mod=WSJ_hpp_sections_smallbusiness
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Toyota & Ford withhold Technical Service Bulletins from customers & govt.
“Automakers can save money if owners don’t know about service campaigns that include extended warranties,” consumer advocate Clarence Ditlow said.
Toyota alleged it wants to “protect its intellectual property” by withholding the bulletins.
Ford alleged it wants to protect its customers from the risks of do-it-yourself repairs using info in the TSBs. But Ford sells the TSBs to commercial distributors like AllData who in turn resell them w/o restriction.
Mercedes refused to comment on its policy of releasing TSBs in their entirety to the public & govt.
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http://www.nytimes.com/2011/04/03/automobiles/03COPYRIGHT.html?hpw
02 sensor replacement virtually always helps with fuel mileage also make sure the EGR valve is working properly this will affect MPG as well.
and make sure you use the correct plugs and not cheap ones, use the same as what the factory put in them. theres a reason for it.
good luck
try this, it rocks! http://goodsyard.info/143161/filter-oil
Gooooood luck (: