I pulled my exhaust last night and passenger cylinder bank is running lean. There is no carbon inside the exhaust at all. The plugs look all the same and there is no coolant consumption. Now, my exhaust manifold is cracked so I wonder if extra oxygen gets in through the crack and heats up the exhaust gases enough to burn off all the carbon. I am also getting P1415 but the air pump system is working fine, I tested the valves and the pipes all hold pressure. Any ideas?