Cylinder Leakage Test

Perform a cylinder leakage test by injecting regulated shop air into the cylinder head's spark plug hole, then visually searching and listening for a leak. The valves, rings, and head gasket seal the combustion chamber. The intake valve leads to the intake manifold, and the exhaust valve leads to the exhaust tailpipe. The piston rings lead to the crankcase and the PCV valve in the valve cover. The head gasket between the head and the block seals the cylinder and the engine's cooling system.

Cylinder leakage test.

By introducing compressed air into the combustion chamber through the spark plug hole, we're able to listen and see any air escaping through one of these areas.

If the intake valve were not seating correctly, air would escape past the valve and into the intake manifold. Air heard at the throttle plate indicates a faulty intake valve at that particular cylinder as the problem. If air is heard escaping through the tailpipe, the exhaust valve is defective, probably burned. If air is escaping through the PCV outlet, the piston rings are faulty. If air bubbles appear from the radiator neck the head gasket (most likely), the cylinder head, or the block's deck are at fault. Always refer to the manufacturer's specifications before performing any automotive test.