Ignition Coil Stihl Chainsaw (5 Pro Tips For Quick Testing)

I once spent a frustrating afternoon wrestling with my Stihl chainsaw, convinced the fuel line was clogged. I took it apart, cleaned everything meticulously, and put it back together… only to have it sputter and die again. Turns out, the culprit was a tiny crack in the ignition coil, a part I hadn’t even considered. This experience taught me a valuable lesson: understanding how to quickly test your ignition coil can save you a ton of time and frustration. So, let’s dive into how to troubleshoot your Stihl chainsaw’s ignition coil.

Ignition Coil Stihl Chainsaw: 5 Pro Tips for Quick Testing

An ignition coil is a critical component in your Stihl chainsaw, responsible for generating the high-voltage spark needed to ignite the fuel-air mixture in the cylinder. A faulty ignition coil can lead to a no-start condition, weak spark, or intermittent engine performance. I’m going to share five pro tips for quick testing, ensuring you can diagnose and address ignition coil issues efficiently.

Understanding the Ignition System Basics

Before diving into testing, it’s essential to understand the basic workings of the ignition system. The ignition coil receives a low-voltage current from the chainsaw’s magneto. It then amplifies this voltage to thousands of volts, creating a spark at the spark plug. This spark ignites the fuel-air mixture, driving the piston and powering the chainsaw.

A healthy ignition system is vital for optimal chainsaw performance. When the ignition coil malfunctions, it disrupts this process, leading to starting problems or reduced power. I often tell people to think of it as the heart of the chainsaw – if it’s weak, the whole system suffers.

Tip 1: Visual Inspection for Obvious Damage

The first step in testing your Stihl chainsaw’s ignition coil is a thorough visual inspection. Look for signs of physical damage, such as cracks, burns, or melted plastic. These are often indicators of a failing coil.

Cracks: Cracks in the coil housing can allow moisture to penetrate, leading to short circuits and reduced performance. I’ve seen coils with hairline cracks that were almost invisible but caused significant issues.
Burns: Burn marks or melted plastic suggest the coil has overheated, which can damage the internal windings and render it unusable. Overheating can occur due to prolonged use or electrical faults.
Corrosion: Check the coil terminals for corrosion. Corrosion can impede the flow of electricity, resulting in a weak spark. Clean the terminals with a wire brush or electrical contact cleaner if corrosion is present.

During a recent logging project, one of my team members reported his chainsaw wouldn’t start. A quick visual inspection revealed a crack in the ignition coil housing. Replacing the coil immediately resolved the issue, saving us valuable time in the field.

Takeaway: A simple visual inspection can often reveal obvious damage that points directly to a faulty ignition coil.

Tip 2: Testing Spark Plug Condition and Gap

Before suspecting the ignition coil, it’s crucial to rule out the spark plug as the culprit. A fouled or improperly gapped spark plug can mimic the symptoms of a bad ignition coil.

Remove the Spark Plug: Carefully remove the spark plug from the cylinder head using a spark plug wrench.
Inspect the Spark Plug: Examine the spark plug for signs of fouling, such as carbon buildup, oil deposits, or excessive wear. Clean the spark plug with a wire brush or replace it if necessary.
Check the Spark Plug Gap: Use a spark plug gap tool to ensure the gap between the electrode and the ground electrode is within the manufacturer’s specifications. The correct gap is typically between 0.020 and 0.025 inches (0.5 to 0.6 mm) for Stihl chainsaws, but always consult your owner’s manual for the exact measurement.
Test the Spark Plug: Connect the spark plug to the spark plug wire and ground the spark plug against the engine block. Pull the starter cord and observe the spark. A strong, blue spark indicates a healthy spark plug. A weak, yellow spark or no spark suggests the spark plug is faulty and needs replacement.

I remember a time when my chainsaw kept cutting out mid-cut. I was convinced it was a fuel issue, but after replacing the fuel filter and cleaning the carburetor, the problem persisted. Finally, I checked the spark plug and found it was heavily fouled with carbon deposits. Replacing the spark plug solved the issue immediately.

Takeaway: Always check the spark plug’s condition and gap before assuming the ignition coil is the problem.

Tip 3: Using a Spark Tester for a Quick Diagnostic

A spark tester is a simple and inexpensive tool that allows you to quickly check the strength and consistency of the spark generated by the ignition coil. It provides a more reliable test than grounding the spark plug against the engine block.

Connect the Spark Tester: Disconnect the spark plug wire from the spark plug and connect it to the spark tester. Ground the spark tester to the engine block.
Pull the Starter Cord: Pull the starter cord and observe the spark gap on the tester. A strong, consistent spark indicates a healthy ignition coil. A weak, intermittent spark or no spark suggests the ignition coil is faulty.
Adjust the Gap: Some spark testers allow you to adjust the gap to simulate the resistance of the spark plug. Increasing the gap can help identify a weak ignition coil that can’t produce a strong enough spark to jump the gap.

I find spark testers particularly useful in diagnosing intermittent ignition problems. Sometimes, the chainsaw will start and run fine for a few minutes before cutting out. A spark tester allows me to monitor the spark continuously and identify any drops in voltage or interruptions in the spark.

Takeaway: A spark tester provides a quick and reliable way to assess the performance of the ignition coil.

Tip 4: Measuring Resistance with a Multimeter

A multimeter is a versatile tool that can be used to measure the resistance of the ignition coil windings. This test can help identify short circuits or open circuits within the coil.

Disconnect the Ignition Coil: Disconnect the ignition coil from the chainsaw. Make sure the chainsaw is turned off and the spark plug wire is disconnected for safety.
Set the Multimeter: Set the multimeter to the ohms setting (Ω).
Measure Primary Resistance: Connect the multimeter leads to the primary terminals of the ignition coil. The primary resistance should be low, typically between 0.5 and 2 ohms. Refer to your Stihl chainsaw’s service manual for the exact specification.
Measure Secondary Resistance: Connect the multimeter leads to the secondary terminals of the ignition coil (the spark plug wire terminal and the coil body). The secondary resistance should be higher, typically between 2,000 and 10,000 ohms. Again, consult your service manual for the correct range.
Interpret the Results: A reading outside the specified range indicates a faulty ignition coil. A reading of zero ohms suggests a short circuit, while an infinite reading suggests an open circuit.

I once encountered a chainsaw that would start but ran poorly, lacking power and misfiring frequently. The spark was weak, but the spark plug was new and properly gapped. Using a multimeter, I measured the secondary resistance of the ignition coil and found it was significantly lower than the specified range. Replacing the ignition coil resolved the issue, restoring the chainsaw’s power and performance.

Takeaway: Measuring the resistance of the ignition coil windings with a multimeter can help identify internal faults that are not visible during a visual inspection.

Tip 5: Checking the Air Gap Between the Ignition Coil and Flywheel

The air gap between the ignition coil and the flywheel is crucial for proper ignition timing. If the air gap is too large or too small, it can affect the strength and timing of the spark.

Locate the Air Gap: The air gap is the small space between the ignition coil and the flywheel. It’s typically located on the side of the flywheel.
Use a Feeler Gauge: Use a feeler gauge to measure the air gap. The correct air gap for most Stihl chainsaws is between 0.010 and 0.014 inches (0.25 to 0.35 mm). Consult your owner’s manual for the exact specification.
Adjust the Air Gap: If the air gap is not within the specified range, loosen the mounting screws that hold the ignition coil in place. Use the feeler gauge to set the correct air gap and then tighten the mounting screws.

I’ve seen cases where the ignition coil was not properly aligned with the flywheel, resulting in a weak or erratic spark. Adjusting the air gap to the correct specification restored the chainsaw’s performance. I even created a simple jig using a piece of cardboard cut to the correct thickness to ensure the air gap was consistent across all my chainsaws.

Takeaway: Ensuring the correct air gap between the ignition coil and the flywheel is essential for proper ignition timing and spark strength.

Additional Tips for Stihl Chainsaw Ignition Coil Troubleshooting

Here are some additional tips to help you troubleshoot ignition coil problems in your Stihl chainsaw:

Check the Wiring: Inspect the wiring connecting the ignition coil to the chainsaw’s electrical system. Look for frayed wires, loose connections, or damaged insulation. Repair or replace any damaged wiring.
Test the Kill Switch: The kill switch is designed to ground the ignition coil, preventing it from generating a spark. A faulty kill switch can cause the chainsaw to not start or to cut out intermittently. Disconnect the kill switch wire from the ignition coil and try starting the chainsaw. If the chainsaw starts, the kill switch is likely faulty and needs replacement.
Consider Environmental Factors: Moisture and humidity can affect the performance of the ignition coil. If you’re working in wet conditions, try drying the ignition coil with a clean cloth or compressed air.
Use Genuine Stihl Parts: When replacing the ignition coil, always use a genuine Stihl part. Aftermarket parts may not meet the same quality standards and can lead to premature failure. I learned this the hard way after installing a cheap aftermarket coil that failed after only a few hours of use.

Common Mistakes to Avoid

Assuming the Ignition Coil is Always the Problem: Don’t immediately assume the ignition coil is the issue. Always check the spark plug, fuel system, and other components first.
Ignoring the Air Gap: The air gap is a critical adjustment that is often overlooked. Always check and adjust the air gap when troubleshooting ignition problems.
Using the Wrong Tools: Using the wrong tools can damage the ignition coil or other components. Always use the correct tools for the job, such as a spark plug wrench, feeler gauge, and multimeter.
Forgetting Safety Precautions: Always disconnect the spark plug wire and turn off the chainsaw before working on the ignition system. This will prevent accidental starting and electric shock.

Real-World Case Studies

Case Study 1: Intermittent Starting Problem: A customer brought in a Stihl chainsaw that would start sometimes but not others. The spark plug was new, and the fuel system was clean. Using a spark tester, I found that the spark was intermittent. Measuring the resistance of the ignition coil with a multimeter revealed that the secondary resistance was fluctuating. Replacing the ignition coil resolved the intermittent starting problem.
Case Study 2: Weak Spark and Poor Performance: A logger complained that his Stihl chainsaw lacked power and misfired frequently. The spark was weak, and the engine was difficult to start. After checking the spark plug and fuel system, I measured the air gap between the ignition coil and the flywheel. The air gap was too large. Adjusting the air gap to the correct specification restored the chainsaw’s power and performance.
Case Study 3: No Spark After Rain: A homeowner reported that his Stihl chainsaw wouldn’t start after a heavy rain. A visual inspection revealed a crack in the ignition coil housing. Moisture had penetrated the crack, causing a short circuit. Replacing the ignition coil resolved the issue.

Maintaining Your Stihl Chainsaw Ignition System

Proper maintenance can help prevent ignition coil problems and extend the life of your Stihl chainsaw. Here are some tips:

Keep the Chainsaw Clean: Clean the chainsaw regularly to remove dirt, debris, and moisture. Pay particular attention to the ignition coil and surrounding area.
Store the Chainsaw Properly: Store the chainsaw in a dry, well-ventilated area to prevent corrosion and moisture damage.
Use Fresh Fuel: Use fresh, high-quality fuel and oil. Old or contaminated fuel can damage the engine and affect the ignition system.
Replace the Spark Plug Regularly: Replace the spark plug according to the manufacturer’s recommendations. A worn or fouled spark plug can put extra strain on the ignition coil.
Inspect the Ignition Coil Regularly: Inspect the ignition coil for signs of damage or wear. Replace the ignition coil if you notice any cracks, burns, or corrosion.

Safety Considerations

Working on a chainsaw can be dangerous. Always follow these safety precautions:

Wear Safety Glasses: Wear safety glasses to protect your eyes from flying debris.
Wear Gloves: Wear gloves to protect your hands from cuts and abrasions.
Disconnect the Spark Plug Wire: Disconnect the spark plug wire before working on the ignition system to prevent accidental starting.
Work in a Well-Ventilated Area: Work in a well-ventilated area to avoid inhaling fumes.
Follow the Manufacturer’s Instructions: Always follow the manufacturer’s instructions when working on your chainsaw.

Conclusion

Testing your Stihl chainsaw’s ignition coil doesn’t have to be a daunting task. By following these five pro tips – visual inspection, spark plug check, spark tester, multimeter test, and air gap adjustment – you can quickly diagnose and address ignition coil issues. Remember to prioritize safety, use the right tools, and consider all possible causes before replacing the ignition coil. With a little knowledge and the right approach, you can keep your Stihl chainsaw running smoothly for years to come. And who knows, you might even save yourself a frustrating afternoon like the one I had!

Now, go forth and conquer those logs, armed with the knowledge to keep your chainsaw’s spark alive!

Ignition Coil Stihl Chainsaw (5 Pro Tips for Quick Testing)