Cylinder Leakage Detection

WARNING: This page is about a different car, the 2004 Ford Focus. However, it is still accessible from the selected car via links, so may be relevant.

When a cylinder produces a low reading, use Special Tool 303-F012 to help pinpoint the exact cause.

The special tool is inserted in the spark plug hole, the piston is brought up to dead center on the compression stroke and compressed air is admitted.

Once the combustion chamber is pressurized, the special tool will read the percentage of leakage. Leakage exceeding 20% is excessive.

While the air pressure is retained in the cylinder, listen for the hiss of escaping air. A leak at the intake valve will be heard in the throttle body. A leak at the exhaust valve can be heard at the tailpipe. Leakage past the piston rings will be audible at the positive crankcase ventilation (PCV) connection or oil filler opening. If air is passing through a blown head gasket to an adjacent cylinder, the noise will be evident at the spark plug hole of the cylinder into which the air is leaking. Cracks in the cylinder block or gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator.