How to check spark plug

 Here’s a simple guide to check an ignition coil (used in cars, bikes, generators, etc.) using basic tools like a multimeter:

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🔧 How to Check Ignition Coil (Step-by-Step)

✅ Tools Needed:

Digital multimeter (DMM)

Screwdriver/spanner

(Optional) Test light or spark tester

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🔍 There are 2 Types of Coil Checks:

1. Primary Coil (Low voltage side)

2. Secondary Coil (High voltage side)

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🧪 1. Primary Coil Resistance Test

Steps:

1. Set multimeter to Ohms (Ω).

2. Disconnect the + and – terminals of the coil (primary wires).

3. Place probes on the positive (+) and negative (–) terminals.

Normal Reading (Typical Values):

0.4 to 2 ohms (Check vehicle manual for exact value)

⚠️ If reading is 0 ohm or infinite (OL) → coil is shorted or open → Replace it.

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🧪 2. Secondary Coil Resistance Test

Steps:

1. Place one probe on the coil tower (where the HT lead/spark plug wire connects).

2. Place the other probe on the negative (–) terminal of the coil.

Normal Reading:

5kΩ to 20kΩ (5000 to 20000 ohms)

⚠️ If there's no continuity or infinite reading, the coil is faulty.

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🔥 3. Spark Test (Practical Method)

Steps:

1. Remove spark plug and connect it to the ignition wire.

2. Ground the spark plug body to engine/frame.

3. Crank the engine or use kick start.

4. Look for strong blue spark at the plug gap.

⚠️ No spark or weak orange spark = possible bad coil or CDI/ECU issue.

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📌 Common Ignition Coil Problems:

Symptom Likely Issue

No spark Coil is open/shorted

Weak spark Internal winding leak

Misfiring when hot Coil failing under heat

Engine won’t start Coil or control module

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⚠️ Safety Tip:

Never check spark by holding the wire with bare hands — ignition voltage is around 20,000V or more, it can give a severe shock.