High all. My son's 1999 DOHC has just about got me whipped. It has been one thing after another and just when I think I have it all straightened out something else pops up. I checked his mileage a while back and it has been averaging 12 to 16 mgp. I tried to blame that on a heavy foot and intown driving. I just filled it up and he drove 28.3 miles, I filled it back up and he used 3.15gal. Thats 8.98 MPG . I read a post a while back someone said they were getting 8MPG and I laughed to my self saying no way. I asked my son if he was letting his friends siphon the gas out . I was not happy with the 16mpg but now I am at my wits end. The car runs good. Has no codes. Fuel trim values and O2 raedings look good. Tires are at rated air pressure. Trans rebuilt, brakes not dragging as far as I can tell. If the brakes were dragging that bad they would be on fire. I do notice a rich smell from the exhaust and inside the pipe is fairly heavy with carbon although you don't see any smoke. The engine has good compression and recent plugs. I am at a loss to figure this out. I am going to start over in the morning and pull the plugs to see how they look. Any ideas would be appreciated.