Ranger 2WD V6-245 4.0L VIN X SFI (1997)
Compression Check: Testing and Inspection
Cylinder Leakage Test
When a cylinder produces a low reading, the use of Rotunda Engine Cylinder Leak Detection/Air Pressurization Kit 014-00708 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 (TDC) 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 will be audible in the throttle body. A leak
by the exhaust valve can be heard at the tail pipe. Leakage past the piston rings will be audible at the positive crankcase ventilation (PCV) connection. If
air is passing through a blown head gasket to an adjacent cylinder, the noise will be evident at the I spark plug hole of the cylinder into which the air is
leaking. Cracks in the cylinder block, or head gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator. To detect a
cracked cylinder wall, it may be necessary to remove air supply at tool and move piston to BDC to expose full length of cylinder bore.
