In the picture you can see two bolts that were placed on the left and right side of the exhaust in front of the main catalytic converters. The black bolt was on the driver side and the bolt that isn't black is on the passenger side. I had misfires on the driver side engine only and you can see what it did to the exhaust. So this is a warning to all if your car is running rich or lean. The passenger bolt is how the exhaust should look inside. The bolt should look rusted but not black like the driver side it means to much fuel was in the exhaust.