Mercury MerCruiser Service Manual page 285

6. Apply 138–206 kPa (20–30 psi) of air pressure through the adapter hose into the cylinder to be tested. Keep the crankshaft
from rotating.
7. Test result interpretation:
Possible Cause
Leaking intake valve
Leaking exhaust valve
Leaking piston or piston rings
90-8M0099748 eng DECEMBER 2015
Test Result
Air is heard leaking up through the intake manifold at the throttle body.
Air is heard leaking into the exhaust system.
A high volume of air leaks into the test cylinder's rocker arm cover and can be felt flowing
out of the oil fill or breather cap. (Low volume air bleed past the rings is normal.)
© 2016 Mercury Marine
Engine Troubleshooting
Page 3C-13