Compression Test Results Interpreter

Compression test results interpreter output shows how evenly the cylinders build pressure and which readings fall outside the limits you enter. It keeps zero readings in their proper cylinder positions and rejects invalid entries instead of hiding them.

What the Numbers Mean

• Absolute pressure: Compare every cylinder with the minimum value in the service information for your exact engine.
• Cylinder balance: A Bosch compression-tester manual gives a general screen in which the lowest cylinder is at least 90% of the highest. The vehicle maker's limit comes first.
• Even but low readings: Similar numbers can still be below specification because of test setup, valve timing, engine wear, or another shared cause.
• One or more low cylinders: Repeat the dry test before using a wet compression test or cylinder leak-down test to narrow the cause.

Make Every Reading Comparable

Follow the vehicle and tester instructions before relying on the result. The Bosch procedure calls for a warm engine, all spark plugs removed, a wide-open throttle, disabled ignition and fuel systems, and the same number of compression strokes for each cylinder. The correct way to disable fuel and spark depends on the vehicle, so use its service procedure.

Read Low-Cylinder Patterns Carefully

A dry test shows that pressure is low, but it does not name the failed part. Bosch advises adding the specified small amount of oil and repeating the test when readings are low. A large increase can point toward piston-ring sealing. Little change can point toward valves or related parts. A leak-down test can locate escaping air more directly.

Do Not Diagnose from PSI Alone

Compression varies by engine design, test speed, temperature, throttle position, gauge, altitude, and valve timing. This tool compares the values you provide. It cannot replace the engine's minimum-pressure specification or the correct diagnostic procedure.