Relative Compression — Cranking Amps

What it tells you

Clamp an amp probe on the battery lead, disable the injectors, and crank: every compression stroke loads the starter, drawing one current peak per cylinder. Even peaks mean a balanced engine; one low hump singles out the weak cylinder — found in thirty seconds, without pulling a single plug.

Healthy vs fault

Toggle Fault overlay on the scope above to drop the faulty capture over the healthy one. Seeing both traces on the same graticule is how you train your eye for the difference — the deviation that names the fault.

Symptoms this catches

• ▸misfire
• ▸rough idle
• ▸low power
• ▸compression
• ▸weak cylinder
• ▸engine balance

Watch the walkthrough

Kits that capture this signal