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!