Properly Checking and Testing Engine Compression

A compression check indicates the condition of the top end of your engine, consisting of the pistons, rings, valves and head gaskets. More specifically, a compression check can help you narrow down a loss of compression due to worn-out piston rings, defective valves or a blown head gasket. The engine should be warmed up to the normal operating temperature to check compression. The battery should also be fully charged to perform the tests.

Clean the area around the spark plugs very thoroughly before removing them from the engine. Compressed air is best for this, if available, if not a small brush, or bicycle pump will get the job done as well. Make sure you use eye protection whenever using compressed air. The idea is to get these areas as clean as possible, preventing any dirt from getting down into the cylinders when removing the spark plugs, or performing the compression test.

Remove all the spark plugs from the engine, and set them aside out of your way. Carefully, block the throttle wide open. There are many ways to achieve this, just be careful not to damage anything in the process. You will need to disconnect the ignition system, the easiest way is to unplug the primary wires from the coil or coil packs. Also, disconnect the fuel injection system by unplugging the connector to the injector wiring harness.