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

tires inflated properly. no service lights on.

by in Coal Township, PA on December 12, 2011
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3 answers 3 comments
ANSWER by , December 12, 2011
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?
COMMENT by , December 13, 2011
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.
ANSWER by , January 11, 2013
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
ANSWER by , December 16, 2011
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.
COMMENT by , December 16, 2011
have tried fuel treatments. not z max though. Thank you.
COMMENT by , December 28, 2011
no problem let me know how it turns out.