02/04/2026
A compression test is a diagnostic check that measures how much pressure each cylinder in your engine can build when the engine is cranking.
Inside your engine, each cylinder compresses a mix of air and fuel before ignition. A compression tester (a gauge screwed into the spark plug hole) measures how well that cylinder can hold and build pressure.
• High, even pressure = healthy cylinder
• Low or uneven pressure = something’s wrong internally.
When a cylinder misfires, it means combustion isn’t happening properly. That can be caused by:
• Ignition issues (spark plugs, coils)
• Fuel issues (injectors)
• Mechanical problems (this is where compression testing comes in)
A compression test helps confirm or rule out mechanical failure.
If a cylinder has low compression, it can point to:
• Worn or broken piston rings
• Burnt or leaking valves
• Blown head gasket
• Cracked cylinder head
These issues stop the cylinder from sealing properly, so it can’t build enough pressure to ignite fuel → causing a misfire.
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