Compression test results

[free5ty1e]

Whats up -

Borrowed my friend's compression tester this past weekend and checked out my EJ22T in the middle of replacing the spark plugs/wires. I got readings between 139-155psi (cylinder 2 being the strongest). What should these readings be on a healthy engine that's not 10 years old? Am I still OK or are my rings done?

How is this figured, anyway? At 8.0:1 CR and with no boost, shouldn't the cylinder pressures be around 8*14.7=117.6psi? I'm obviously not calculating this right, anyone know how that works?

[vrg3]

Usually what you're more concerned with is the difference between cylinders. If one cylinder has much greater or much less compression than the others, that's a problem.

I don't know how you'd calculate the expected compression... I do know that the factory service manual specifies for the EJ22T a compression between 142 and 171 psi, with a service limit of 114 psi, and a maximum difference between cylinders of 28 psi.

The absolute number isn't always that meaningful because a lot of cheap compression gauges are poorly calibrated (or can easily lose their calibration if stored in a toolbox where they bounce around), and also because the connection at the spark plug hole often leaks a little. The strength of the starter motor also affects the final pressure you measure.

If you really want to know what's going on, a leakdown test is a better way to check the engine's health.

But in any case it sounds like your engine is fine.

[free5ty1e]

OK I got it... yeah thats not too much of a spread for a 10 year old car. Thanks for the info - I'm new to leakdown tests though, how would one go about doing that?

[vrg3]

To do a leakdown test, you first bring the cylinder you're testing to TDC of the compression stroke so all the valves are closed. Then you apply regulated compressed air to the spark plug hole to pressurize the combustion chamber, and measure how much pressure leaks out. If you're really observant, you can also figure out where the leaking air is going.

It ought to be possible to build your own leakdown tester with an air compressor, a pressure regulator, a pressure gauge, and some plumbing, but I've never tried it.

[free5ty1e]

Ah, thank you, I see the light now. I'll check into that this weekend. I appreciate the help.