Section 03-00: Engine, Service
1996 All F-150, F-250, F-350, F-Super Duty and Bronco Vehicles Equipped with 4.9L, 5.0L, 5.8L or 7.5L Gasoline Engines, and 7.3L Diesel Engines Workshop Manual

Cylinder Leakage Detector


When a cylinder produces a low reading, the use of Rotunda Pressurization Kit 014-00705 or equivalent will be helpful in pinpointing the exact cause.

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

Once the combustion chamber is pressurized, a special gauge will read the percentage of leakage. Leakage exceeding 20 percent is considered excessive.

While the air pressure is retained in the cylinder, listen for the hiss of escaping air. A leak by the intake valve (6507) will be audible in the throttle body (9E926). A leak by the exhaust valve (6505) can be heard at the tail pipe. Leakage past the rings will be audible at the positive crankcase ventilation (PCV) connection. If air is passing through a blown 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 (6010), or gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator (8005).