2003 Chevrolet Avalanche 1500 Q&A
2003 Chevrolet Avalanche 1500 Question: Why is my gas mileage dropping, 2mpg seems to be running smooth.
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? - patrick mannion
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. - brian23703
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 - BIGDOG9791