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2003 Chevrolet Avalanche 1500 Question: Why is my gas mileage dropping, 2mpg seems to be running smooth.

 

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RickW1219, Coal Township, PA, December 12, 2011, 20:13
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tires inflated properly. no service lights on.

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  • Answer #1

    patrick mannion from Greg Solow's Engine Room, December 12, 2011, 21:32
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    Brand of fuel, winter and summer grades all can make a small difference but 2 mpg is a lot.You would need to look at fuel trim figures on a scan tool to see if long term fuel trims are out of spec but not to the point of setting a code. Is the Chevy high mileage engine would have less friction but the injectors may wear. Are the air filter and spark plugs fresh?

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    RickW1219, December 13, 2011, 04:47
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    air filter is fresh, spark plugs are not,90000 miles,just cleaned throttle body thought that was the problem was idling roughly and stalling. IT didn't drop all at once but when I got it I was getting 16mpg and it is down to 14 sometimes less. Usually on a trip on the Interstate I could get 18,now I don't see a difference. I was wondering has the quality of fuel gone down that much and more ethanol in the fuel. Thank you for your time.

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  • Answer #2

    December 16, 2011, 03:22
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    you might just have carbon build up from poor quality gas, have you tried a fuel treatment, i recomend zmax. awsom stuff helped me with my impalla as it also had a 2mpg drop, and its for both fuel and oil. its about $30 at any parts store.

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    RickW1219, December 16, 2011, 06:15
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    have tried fuel treatments. not z max though. Thank you.

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    brian23703, December 28, 2011, 00:16
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    no problem let me know how it turns out.

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  • Answer #3

    January 11, 2013, 15:34
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    a mileage loss can be caused by a number of things the most common is tire pressure 5 psi can cause 2 to3 mile to the gallon loss it may be caused by need of maintenanc suh as tune up oh a bad sensor

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