Relative Compression

Introduction:

Relative compression testing is part of the standard AA vehicle inspection. This is a very useful step in the diagnostic process, which can save you a lot of time and money when working on a vehicle.

The Relative Compression test is to confirm if there are any mechanical issues in the engine or not.  It can also be a good, quick first step before any transducer testing as it is quicker to run this diagnostic, than it is to do a traditional compression test with gauge.

The test is relative and only shows relative difference in cylinders compression expressed as percentage toward most good cylinder.

Relative compression test results are dependent upon:

– the compression of each engine cylinder

– the battery condition

– the starter motor condition

– the  condition of electrical circuit elements (cables, connectors etc.)

Apparatuses used:

1. Oscilloscope (lab scope)

2. Factory  Diagnostic scanner.

3. Specialised relative compression tester.

More detailed information is available here:

FUNDAMENTALS OF THE AUTOMOTIVE RELATIVE COMPRESSION TEST

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