What is the effect of removing all spark plugs during a compression test?

Removing all spark plugs during a compression test improves cranking speed, which is essential for obtaining accurate compression readings. When the spark plugs are removed, the engine does not have to overcome the resistance that each cylinder provides during its compression stroke. This decreased load allows the engine starter to crank the engine more easily and at a higher speed, thus enabling the technician to get a more precise indication of the engine's compression levels.

At a higher cranking speed, the engine can build compression more quickly, providing a clearer and more accurate representation of the condition of the cylinders. The readings obtained are more reliable, as any potential dampening effects caused by slow cranking are eliminated. In the context of diagnostics, being able to assess the compression characteristics effectively is vital for determining engine health and performance.