When winter blizzards and freezing temperatures knock out power, a generator that won’t start can turn an emergency into a crisis. Cold weather is especially hard on ignition components like the ignition coil (magneto), often causing no-spark, intermittent power, or complete failure—even if the engine and battery seem fine. We will show you how to test ignition coil components quickly and safely.
Common Symptoms of a Bad Ignition Coil
How do you know if the coil is the issue? Look for these signs:
Difficulty starting: The engine cranks but won’t fire up .
Misfiring: The generator runs roughly or surges under load.
No spark: The most definitive sign that your ignition coil is bad .
Method 1: The Spark Test (Quick Check)
This is the fastest way to check for a faulty magneto.
Safety First: Disconnect the kill switch and any low-oil sensors to ensure they aren't grounding out the system .
Remove the Plug: Take out the spark plug and reconnect it to the spark plug wire.
Ground It: Hold the threaded body of the plug against a bare metal part of the engine (like a cooling fin).
Pull the Cord: Watch the tip of the plug as you pull the starter cord.
Analyze the Spark:
Good: A bright, blue/white spark is visible .
Bad: No spark, or a weak yellow or orange spark, indicates a weak coil that needs replacement .
Method 2: Using a Multimeter (Bench Test)
For a more precise diagnosis, use a multimeter to check ignition coil resistance.
Primary Resistance: Set your meter to ohms (Ω). Connect the leads to the coil's primary terminals (usually the small wires or connectors). You should see a reading of 0.5 to 1.5 Ohms .
Secondary Resistance: Set the meter to the highest ohm scale (Rx1K). Place one lead on the coil's primary wire terminal and the other inside the spark plug boot (where the metal terminal clips on). You should see a reading of approximately 16,000 to 17,000 Ohms (16-17 kΩ) .
Result: If your readings are far outside these ranges, the coil is defective.
Replacing the Coil
If your tests confirm a bad coil, replacement is straightforward. You must set the air gap correctly during installation. Using a business card as a spacer between the coil and the flywheel magnet usually achieves the perfect gap of 0.010 to 0.020 inches .
Don't let ignition failure leave you in the dark. A quick test can save you time and get your power backup running again. Click here to check our Generator Ignition Coil.