14.2 mpg highway & no error codes or lights on 2004 Buick Rainier

fuel mieage on local & highway, using high or low grade fuel, increasingly getting worse. Bought from dealer 1 year ago doing 16.0mpg, now down to 14.2mpg. no signs anywhere. mechanics won't look at it without a code to trace.

by in San Diego, CA on July 11, 2010
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2 answers
ANSWER by , July 11, 2010
Check this government website for 2WD Rainier. http://www.fueleconomy.gov/feg/findacar.htm They are not brilliant for MPG but some tires even can help fuel economy, (less rolling resistance). I wonder on a scan tool what the fuel trim figures are Long Term Fuel Trim figures show if your car's computer is adding or taking away fuel which may not yet have set a code.
ANSWER by , July 31, 2010
you may want to seek professional help because my 2006 AWD Rainer needed the stabiltrac serviced and after that the fuel mileage went from 15.7 to 19 mpg highway