Have a 1997 chevy 2500 express with the 5.7 ltr. Thing runs fine and no check engine light is on! but I'm getting really bad MPG (9mpg). the guy i bought it from said he was getting 18 hwy. So checked the exhaust very little airflow coming out. so I replaced the muffler. More air flow was noticed it was quit a bit louder and then the check engine light came on. code was for a mass air flow sensor, replaced that and still had the engine light on! ended up replaceing a oxg sensor. light went out, but still 9mpg! called chevy garage and they said to check timming and put at 26degrees. did that still 9mpg! went to re-time one more time and noticed dist. movement. pulled it and gear on the bottom was wore out, so bought a new one and put it in and timed it to 24 degrees. could not get 26 it would run rough! MPG went up to 11 !
could really use some imput or help, PLEASE!!