Cylinder Leakage Testing
During a cylinder leakage test shop air is injecting into the cylinder.Then the technician would begin searching for any place air may be leaking. We know the different places that must be sealed in a combustion chamber. We have the intake valve that leads to the intake manifold. We also have it's companion the exhaust valve that leads to the exhaust tail pipe. There's the piston rings that lead to the crankcase and the PCV valve in the valve cover. Then there's the head gasket and the surface between the head and the block leading to the engines cooling system.
So if we introduce compressed air into the combustion chamber through the spark plug hole we would be able to listen for the air escaping through one of these areas. For instance, if the intake valve were not seating correctly air would escape past the valve and into the intake manifold. If you opened the throttle body and heard air escaping during a cylinder compression test you just identified the intake valve of that particular cylinder as the problem. If you heard air escaping through the tailpipe the exhaust valve is probably burned and if air is escaping through the PCV valve the piston rings are faulty. If air bubbles appear from the radiator neck the head gasket (most likely), cylinder head, or the block's deck are at fault. Always refer to the manufacturers specifications before performing any automotive test.
