How to compression test the engine

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When performing compression tests, it's imperative that the tests be done with:

-A fully charged and properly rated cranking battery

-Engine warmed up to Operating Temperature if possible (Test can be performed on a cold engine as well, I prefer the warmed up engine method)

-All Spark Plugs Removed

-Plug wires on Spark Tester or grounded with jumper leads

-Throttle plate at the WOT Position

Insert compression tester into #1 spark plug opening, and crank the engine until the reading no longer rises. Record reading.

Repeat above step for each cylinder.

Compare numbers. They should be +/- 5% of each other.

You can take it a step further by squirting a little oil in each cylinder through the spark plug hole and re-test to check the condition of the rings.

Additional reading...

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