How to compression test the engine

[Don65Stang]

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... http://www.7173mustangs.com/thread-compression-test

 

[droptop73]

Grounding the coil wire works too.

 

[will e]

If you squirt oil, use a small syringe and try to be consistent on how much you use in each cyl

 

[caspianwendell]

If you squirt oil, use a small syringe and try to be consistent on how much you use in each cyl

The oil is for testing a very low or no compression...if adding oil brings up the compression then it's a ring problem, if it remains unchanged then could be burnt valve, collapsed lifter, hole in piston, etc.