COMPARE / IGNITION

IGNITION COIL COMPARISON

Compare coil dwell, primary current, firing demand and burn behavior without swapping parts.

ESTIMATED SETUP3–5 min1–2 channels
WHY BEFORE DISASSEMBLY

CAPTURE THE SYSTEM
AS IT FAILED.

Coil swapping can move connectors, boots and wiring enough to hide an intermittent fault. Capturing comparable cylinders first preserves the symptom and helps separate command, coil saturation, secondary demand and combustion-related differences.

Reading the signal

Good waveform

Under matched conditions, comparable coils show consistent dwell, primary-current rise and firing/burn behavior appropriate to their design. Compare cylinders with the same probe arrangement and operating load.

Faulty waveform

Missing current, early saturation, erratic firing events or a consistently different burn period deserve investigation. Coil supply, driver behavior, plug gap, mixture and cylinder pressure can each affect the pattern; an electrical trace alone does not identify the failed part.

Common mistakes

AVOID THE
FALSE CLUE.

PREPARE THE TEST

✓ Identify COP, wasted-spark or distributor system✓ Use probes rated for the expected voltage✓ Keep pickup position consistent✓ Verify ignition and fuel hazards are controlled

STEP-BY-STEP PROCEDURE

  1. Choose the least invasive approved pickup: primary current, capacitive secondary or manufacturer-specified test point.
  2. Set a trigger that stabilizes one ignition event and leaves room for the firing and burn periods.
  3. Capture the suspect cylinder at idle and, when safe, under the load that causes the complaint.
  4. Measure dwell, peak primary current, firing event, burn duration and oscillation behavior available from the selected pickup.
  5. Capture a known-good cylinder using the identical setup and scale.
  6. Use injector command, contribution testing and plug/boot inspection to confirm whether the difference is electrical or combustion-related before parts removal.
WHAT THIS TEST CANNOT PROVE

Secondary voltage values from capacitive pickups are often comparative, not laboratory-absolute. Coil design strongly affects waveform shape.

⚠ SAFETY / CONNECTION CAUTION

Ignition systems generate dangerous voltage. Use approved pickups; never hold a coil or improvised spark lead during operation.

STOP BEFORE CONDEMNING THE PART

Repeat the capture, verify the circuit under load and use vehicle-specific specifications. Follow with the most direct confirmation test indicated by the evidence.

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