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How can I do a compression test

I do mine when the engine is warm (not too hot to touch). Take all the spark plugs out at once. Open the throttle and choke. Take the coil wire off. Insert your tester adaptor into the first plug hole and make sure it's pretty hand tight. Turn the engine over with the key a few turns until the gauge won't go any higher. That's your dry compression for that cylinder. Write it down and move to cylinder number 2, depending on the engine you have and the cylinder order. Once done with all cylinders note if any variances more than 10 - 15%. If so then squirt a teaspoon full of oil (no more) into each spark plug hole and test them again. This is a wet compression test. If you notice a big difference in your numbers for the cylinder(s) in question, then your rings are probably worn or the cylinder wall is scored. If no change then possible bad valve or head gasket.

That's how I do it anyway.
 
no plugs it ain't gonna start anyway. warm motor then it's wet already. I might add get the gauge that screws in, not the one you have to hold in.

Reset the gauge after every hole and keep the plugs in order or mark them. Here is a link to how to read plugs.

Lastly keep a log of the compression for latter you might need to refer back to it.

Spark Plugs
 
GM changed their recommended procedure before Y2K became a common buzzword. You can do it cold. Min reading within 15% of the max value and no cylinder under 100 psi. This is the 'dry' version. As noted above, a wet version - done after the dry one - can provide insight if an issue is noted.
 
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