Mercury Mariner 8/9.9HP 4-Stroke Factory Service Manual, Page 30Get this manual
Compression Check 1Remove spark plugs2Install compression gauge (a) in spark plug hole3Hold throttle plate at W.O.T4Crank the engine over until the compression
Cylinder Leakage Testing
NOTE: Cylinder leakage testing, along with compression testing, can help the mechanic pinpoint the source of mechanical failure by gauging the amount of leakage in an engine cylinderRefer to the manufactures tester instructions for proper testing procedures
reading peaks on the gaugeRecord the reading5Check and record compression of each cylinder
The highest and lowest reading recorded should not differ by more than 15 (See example test chart below)A reading below 120 psi might indicate total engine wear problemExample of compression test differences Maximum (psi) 180 150 Minimum (psi) 162 127.5
Courtesy of Snap-On-Tools
6Compression check is important because an