Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Engine Compression Test
Perform the following steps to conduct a compression test.
- Conduct the following steps to check cylinder compression.
- Engine should be at room temperature.
- Disconnect wiring from the ignition module.
- Remove the spark plugs.
- Throttle body valve should be wide open.
- Battery should be at or near full charge.
- For each cylinder, crank engine through 4 compression strokes.
- The lowest reading cylinder should not be less than 70 percent of the highest.
- No cylinder reading should be less than 689 kPa (100 psi).
- Normal
Compression builds up quickly and evenly to specified compression on each cylinder.
- Piston Rings
Compression is low on the first stroke, tends to build up on following strokes, but does not reach normal. Compression improves considerably with the addition of oil.
- Valves
Compression is low on the first stroke, does not tend to build up on the following strokes, and does not improve much with the addition of oil. Use approximately 3 squirts from a plunger-type oiler.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.