I bought my 2003 Silverado new. It's a 1500, 6-cly. It now has 58,000 miles, starts and runs as good as it ever did, does not use oil, no knocks or engine rattles. It's never been mistreated and always serviced regularly. The problem is poor gas mileage. I use to get 17-19 MPG. Yesterday I put the pencil to it and I got a whopping 9.9 miles to the gallon. My mechanic(s) say that all the codes and air filter are fine and the tail pipe does not show any unusual soot. They are kind of at a loss to explain what is happening. Anyone ever had this problem or have any ideas what it might be? Any help would be greatly appreciated.

 

Have you put a upgraded exhaust like magnaflow or is everything still stock?

 

Did it drop all at once or was it gradual? Is your odometer correct? Maybe a gas leak. Maybe someone siphoning your gas at night????

 

Is the front air dam in place? Don't have this sister lifted do ya?

Allan

 

Everything is still stock, all original with nothing removed and no leaks. It was more quick than gradual, I think.

 

some of the O2 sensors control the fuel mixture. The MAF sensor also does. It is probably one of the many sensors on the engine malfunctioning but not bad enough to throw a code.