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Sudden Drop in Fuel Economy


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A little history to start with........ I have a 2008 Sierra Denali with a 2.3l whipple supercharger, k&n intake, muffler swap. The whipple has been on for about 2 year now or 13000 miles. Recently I have been experiencing a loss in fuel mileage. I was previously getting around 12 mpg with pretty much city driving. Lately I have been only getting about 10mpg and I don't think I am driving it any different. Now the difference between say this time last year and now is that I recently purchased a GTO and that has become my daily driver and the truck seems to be my weekend ride. Is the fact that the truck sits most of the time and is not driven consistently, be part of the cause of the fuel mileage decrease or could there be something else wrong. And when I say it sits I have really only put like 2500 mile on the truck since January. I have no trouble codes as I scanned it with my autocal handheld and there are no check engine lights. Any idea as to what the cause might be. Could it be just because it sits and only gets driven most of the time on short trips of 5-10 miles most of the time now????

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I thought the same thing on the last tank of gas but I just filled it up and already 40 miles into the new tank I am right at 10mpg. I am going to take it out tonight and put about 30 miles on it and get some highway miles to see if it changes.

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I typically fill it up about once a month and it seems the last tank was really bad and this tank is starting out just as bad. Ill report back this even with what the DTC says the fuel mileage increase to after taking it out for a longer drive and on the highway.

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Well I took it out tonight and put an additional 40-50 miles on it and the mileage has come up some. I am going to clean the air filter and clean the mass air flow sensor as well and see if that helps.

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while you're at it, clean your TB.. with the amount of miles you put on it, i would also put some injector cleaner in the tank, i prefer SeaFoam myself. i only put 6-8 miles per day if that back and forth to work, and when my mileage drops it works for me..

 

good luck

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  • 5 months later...

I made an account just to ask you about your mirrors. Did you just sand down the facts and paint them with a urethane paint? I've been looking for aftermarket ones that are fully paintable with no luck. They look great and I'd love to get my hands on some mirrors like that.

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