How to Test Stihl Ignition Coil with Multimeter: Don’t Miss Out!

When your Stihl chainsaw, brushcutter, or other equipment refuses to start, a faulty ignition coil can be the culprit. The ignition coil is responsible for generating the high voltage spark that ignites the fuel-air mixture in the engine. If the coil is damaged, it won’t produce the necessary spark, leaving your equipment stranded.

This guide will walk you through the process of testing your Stihl ignition coil using a multimeter, helping you diagnose the issue and determine if replacing the coil is the solution.

Understanding the Ignition Coil

The ignition coil is a crucial component in the ignition system of your Stihl equipment. It acts as a transformer, converting the low voltage from the battery into a high voltage spark that ignites the fuel-air mixture in the combustion chamber.

The coil consists of two windings: a primary winding and a secondary winding. The primary winding is connected to the ignition module, while the secondary winding is connected to the spark plug. When the ignition module sends a signal, the primary winding creates a magnetic field, which induces a high voltage current in the secondary winding. This high voltage current then flows through the spark plug, creating the spark that ignites the fuel.

Why Test the Ignition Coil?

Testing the ignition coil is essential when troubleshooting starting problems in your Stihl equipment. A faulty ignition coil can manifest in various ways, including:

• No Spark: The most common symptom of a bad ignition coil is a complete lack of spark at the spark plug.
• Weak Spark: A weak spark may still allow the engine to start, but it will run poorly and may stall easily.
• Intermittent Spark: An intermittent spark can cause the engine to start and stop unexpectedly.

Tools You’ll Need

Before you begin testing your ignition coil, ensure you have the following tools:

• Multimeter: A digital multimeter is essential for measuring the resistance of the ignition coil.
• Spark Plug Wrench: To remove and inspect the spark plug.
• Safety Glasses: Protect your eyes from potential debris.
• Gloves: Protect your hands when working with electrical components.

Testing the Ignition Coil: Step-by-Step

Now, let’s dive into the testing procedure:

1. Disconnect the Spark Plug:

• Use the spark plug wrench to remove the spark plug from the cylinder head.

2. Set the Multimeter to Resistance Mode:

• Turn on your multimeter and select the resistance setting (usually denoted by “Ω”).
• Choose an appropriate resistance range, typically a setting between 200 ohms and 20k ohms.

3. Identify the Ignition Coil Terminals:

• The ignition coil usually has two terminals: one connected to the primary winding and the other to the secondary winding.
• Refer to your equipment’s service manual or online resources for a diagram showing the terminal locations.

4. Measure the Resistance of the Primary Winding:

• Connect the multimeter leads to the primary winding terminals.
• Note the resistance reading displayed on the multimeter.

5. Measure the Resistance of the Secondary Winding:

• Connect the multimeter leads to the secondary winding terminals.
• Note the resistance reading.

6. Compare the Readings to the Specifications:

• Consult your Stihl equipment’s service manual or online resources for the specified resistance values for the primary and secondary windings.
• Compare your readings to the specifications.

7. Evaluate the Results:

• If the resistance readings are within the specified range: The ignition coil is likely functioning correctly. The problem might lie elsewhere in the ignition system, such as a faulty ignition module or a broken spark plug wire.
• If the resistance readings are significantly different from the specifications: The ignition coil may be faulty and needs to be replaced.

Interpreting the Results

Here’s a breakdown of what the readings mean:

• High Resistance: If the resistance is significantly higher than the specified value, it indicates a possible open circuit in the winding. This means the coil cannot conduct electricity properly.
• Low Resistance: If the resistance is significantly lower than the specified value, it indicates a possible short circuit in the winding. This means the coil is not providing enough resistance to the flow of electricity.
• No Resistance: If the multimeter reads “OL” (over-limit) or “0” (zero), it indicates an open circuit or a complete failure of the winding.

Replacing the Ignition Coil

If your testing reveals a faulty ignition coil, replacing it is essential. Here’s what you need to do:

• Purchase a New Ignition Coil: Ensure you get a new ignition coil that is specifically designed for your Stihl model.
• Disconnect the Old Coil: Disconnect the wires connected to the old ignition coil.
• Connect the New Coil: Connect the wires to the new ignition coil, ensuring they are securely connected.
• Reconnect the Spark Plug: Reinstall the spark plug and tighten it securely.
• Test the New Coil: Start the equipment and test if the new ignition coil is functioning correctly.

Troubleshooting after Replacing the Ignition Coil

Even after replacing the ignition coil, you may still encounter starting problems. Here are some additional troubleshooting steps:

• Inspect the Spark Plug: Ensure the spark plug is clean and the gap is set correctly.
• Check the Fuel System: Verify that the fuel tank is full, the fuel lines are clear, and the fuel filter is clean.
• Inspect the Ignition Module: If the problem persists, the ignition module might be faulty.

Final Thoughts: A Spark of Success

By following these steps and using a multimeter, you can effectively test your Stihl ignition coil and determine if it’s the root cause of your equipment’s starting problems. Remember to always prioritize safety and consult your equipment’s service manual for specific instructions and specifications. With a little knowledge and the right tools, you can diagnose and fix ignition coil issues, ensuring your Stihl equipment runs smoothly and efficiently.

Basics You Wanted To Know

Q: Can I test the ignition coil with the engine running?

A: No, it’s dangerous to test the ignition coil with the engine running. The high voltage generated by the coil can be lethal if you come into contact with it. Always disconnect the spark plug before testing the ignition coil.

Q: What are some common causes of a faulty ignition coil?

A: Faulty ignition coils can be caused by several factors, including:

• Heat: Excessive heat can damage the coil’s insulation, leading to short circuits or open circuits.
• Vibration: Frequent vibrations from the engine can cause the coil’s internal components to loosen or break.
• Moisture: Exposure to moisture can corrode the coil’s terminals or windings, causing electrical resistance.
• Age: Over time, the insulation in the ignition coil can deteriorate, leading to failure.

Q: How often should I test my ignition coil?

A: It’s a good idea to test your ignition coil periodically, especially if you notice any starting problems with your Stihl equipment. If you use your equipment frequently in harsh conditions, you may want to test it more often.

Q: Can I repair a damaged ignition coil?

A: It’s not recommended to repair a damaged ignition coil. The internal windings are delicate and difficult to access. It’s usually more cost-effective and safer to replace the entire coil.