12/06/2026 10:54 am
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Automotive Q&A
Relative compression shows one low event—how do you assign it to a cylinder?
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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A relative-compression waveform is quick, but our reports sometimes label the low event as “cylinder 3” without showing how synchronization was established. On engines with uneven firing intervals or variable cranking speed, that can be wrong.
Which sync signal and verification step do you prefer?
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13/06/2026 7:45 am
Capture a known cylinder ignition or injector command on a second channel and use the engine firing order to count from that event. Confirm whether the sync edge represents the start of dwell, firing or injection so the offset is understood. For systems that suppress commands during clear-flood cranking, a pressure pulse or crank-cam reference may be more reliable.
Repeat the capture after moving the sync pickup to another known cylinder when identification matters. Relative compression ranks events; the sync and firing order assign names.
Topic starter
14/06/2026 10:13 am
We added the firing order and sync-edge definition directly to the saved waveform. A V6 case originally labeled cylinder 3 was correctly reassigned to cylinder 5 after counting from injector 1, and the mechanical test confirmed the new assignment.