How to Test Stihl Ignition Coil with Multimeter (3 Pro Tips)
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How to Test Stihl Ignition Coil with Multimeter (3 Pro Tips)
The year is 1926. Andreas Stihl, a name now synonymous with chainsaws, pioneers his first electric chainsaw. Little did he know, his invention would revolutionize forestry and woodworking, setting the stage for a legacy of innovation. Fast forward nearly a century, and the heart of many Stihl chainsaws, the ignition coil, remains a critical component. When your Stihl chainsaw sputters and refuses to roar to life, a faulty ignition coil is often the culprit.
I’ve spent countless hours in the field, felling trees and processing firewood, and I can tell you firsthand that a malfunctioning chainsaw can bring your entire operation to a grinding halt. That’s why knowing how to diagnose and test your Stihl ignition coil is crucial. This isn’t just about fixing a machine; it’s about maintaining your livelihood and ensuring your projects stay on track.
Key Takeaways:
- Understanding Ignition Coil Function: Learn how the ignition coil works to generate the high voltage needed to spark the fuel-air mixture in your Stihl chainsaw.
- Multimeter Mastery: Discover how to use a multimeter to accurately test the primary and secondary resistance of your ignition coil.
- Troubleshooting Techniques: Get pro tips for identifying common ignition coil problems and interpreting your multimeter readings.
- Safety First: Review essential safety precautions to protect yourself while working on your chainsaw.
- DIY vs. Professional Repair: Determine when it’s best to tackle the repair yourself and when to seek professional help.
The Ignition Coil: Heart of Your Stihl Chainsaw
Before we dive into testing, let’s understand what an ignition coil does. Think of it as the heart of your chainsaw’s ignition system. It takes the low voltage from the magneto (or battery in some models) and transforms it into the high voltage needed to create a spark at the spark plug. This spark ignites the fuel-air mixture in the cylinder, powering the engine.
Without a properly functioning ignition coil, your chainsaw simply won’t start. It’s that critical.
Why Test Your Stihl Ignition Coil?
Several symptoms can point to a faulty ignition coil. I’ve experienced them all firsthand:
- No Spark: The most obvious sign. If you pull the starter cord and don’t see a spark at the spark plug, the ignition coil is a prime suspect.
- Difficult Starting: Your chainsaw cranks and cranks but refuses to start, or it starts intermittently.
- Weak Spark: The spark is present but weak, leading to poor engine performance, misfires, and stalling.
- Engine Misfires: The engine runs erratically, with noticeable skips or hesitations.
- Engine Stalling: The engine starts and runs for a short period, then stalls unexpectedly.
Testing your ignition coil with a multimeter helps you pinpoint the problem and avoid unnecessary replacements. It’s a cost-effective way to diagnose the issue and get your chainsaw back in action quickly.
Gathering Your Tools and Materials
Before we get started, you’ll need a few essential tools and materials:
- Multimeter: A digital multimeter is ideal for accurate readings. Make sure it’s in good working condition and the battery is charged.
- Screwdrivers: You’ll need screwdrivers to remove the chainsaw’s cover and access the ignition coil.
- Spark Plug Wrench: To remove the spark plug for testing.
- Safety Glasses: Protect your eyes from debris.
- Gloves: Protect your hands from sharp edges and potential electrical shocks.
- Stihl Chainsaw Service Manual (Optional): A service manual provides detailed diagrams and specifications for your specific Stihl model.
Safety First: Essential Precautions
Working on a chainsaw involves potential hazards. Always prioritize safety:
- Disconnect the Spark Plug Wire: This prevents accidental starting and electrical shock.
- Wear Safety Glasses and Gloves: Protect your eyes and hands from debris and potential hazards.
- Work in a Well-Ventilated Area: Avoid inhaling exhaust fumes.
- Refer to Your Stihl Chainsaw Service Manual: Follow the manufacturer’s instructions for your specific model.
- If Unsure, Seek Professional Help: Don’t hesitate to consult a qualified mechanic if you’re uncomfortable with any step.
Step-by-Step Guide: Testing Your Stihl Ignition Coil with a Multimeter
Now, let’s get down to business. I’ll guide you through the process of testing your Stihl ignition coil step-by-step.
Step 1: Accessing the Ignition Coil
- Locate the Ignition Coil: The ignition coil is typically located near the flywheel, under a protective cover.
- Remove the Cover: Use a screwdriver to remove the screws or fasteners securing the cover.
- Identify the Ignition Coil Terminals: You’ll typically find two terminals: a primary terminal (connected to the magneto or battery) and a secondary terminal (connected to the spark plug wire).
Step 2: Testing the Primary Resistance
The primary resistance test checks the integrity of the coil’s primary winding.
- Set the Multimeter: Set your multimeter to the ohms (Ω) setting, typically in the range of 200Ω.
- Connect the Probes: Place one multimeter probe on the primary terminal of the ignition coil and the other probe on the engine ground (a clean, unpainted metal surface on the engine block).
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Read the Resistance: Observe the reading on the multimeter.
- Expected Reading: The primary resistance should typically be between 0.5 and 2 ohms. Refer to your Stihl chainsaw service manual for the exact specification for your model.
- Reading of Zero or Close to Zero: Indicates a short circuit in the primary winding.
- Reading of Infinity (OL or 1): Indicates an open circuit in the primary winding.
Step 3: Testing the Secondary Resistance
The secondary resistance test checks the integrity of the coil’s secondary winding.
- Set the Multimeter: Set your multimeter to the ohms (Ω) setting, typically in the range of 20,000Ω (20kΩ).
- Connect the Probes: Place one multimeter probe on the spark plug wire terminal of the ignition coil and the other probe on the engine ground.
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Read the Resistance: Observe the reading on the multimeter.
- Expected Reading: The secondary resistance should typically be between 2,000 and 10,000 ohms. Refer to your Stihl chainsaw service manual for the exact specification for your model.
- Reading of Zero or Close to Zero: Indicates a short circuit in the secondary winding.
- Reading of Infinity (OL or 1): Indicates an open circuit in the secondary winding.
Step 4: Interpreting the Results
Now that you’ve taken the readings, let’s interpret the results:
- Readings Within Specification: If both the primary and secondary resistance readings are within the specified range, the ignition coil is likely functioning correctly. The problem may lie elsewhere in the ignition system, such as the spark plug, spark plug wire, or magneto.
- Readings Outside Specification: If either the primary or secondary resistance readings are outside the specified range, the ignition coil is likely faulty and needs to be replaced.
Pro Tip #1: The Visual Inspection
Before you even reach for your multimeter, give the ignition coil a thorough visual inspection. Look for:
- Cracks or Damage: Cracks in the coil’s housing can allow moisture to enter, causing shorts and malfunctions.
- Burn Marks: Burn marks indicate overheating, which can damage the coil’s windings.
- Corrosion: Corrosion on the terminals can interfere with electrical conductivity.
- Loose Connections: Ensure all connections are secure and free from corrosion.
I once had a chainsaw that was constantly misfiring. After a visual inspection, I discovered a tiny crack in the ignition coil housing. Moisture was seeping in, causing intermittent shorts. A new ignition coil solved the problem instantly.
Pro Tip #2: The Air Gap Adjustment
The air gap is the distance between the ignition coil and the flywheel. This gap is crucial for proper ignition timing and spark generation. If the air gap is too wide or too narrow, it can cause starting problems and poor engine performance.
- Locate the Air Gap: The air gap is the small space between the ignition coil and the flywheel.
- Use a Feeler Gauge: Use a feeler gauge to measure the air gap. The specified air gap for most Stihl chainsaws is typically between 0.010 and 0.014 inches (0.25 to 0.35 mm). Refer to your Stihl chainsaw service manual for the exact specification for your model.
- Adjust the Air Gap: If the air gap is not within the specified range, loosen the ignition coil mounting screws and adjust the position of the coil until the air gap is correct. Tighten the mounting screws securely.
I remember one instance where a customer brought in a Stihl chainsaw that refused to start. After checking the ignition coil, I discovered the air gap was way off. Correcting the air gap was all it took to get the chainsaw running smoothly again.
Pro Tip #3: The Spark Test
Even if the resistance readings are within specification, it’s always a good idea to perform a spark test to confirm that the ignition coil is producing a strong spark.
- Remove the Spark Plug: Use a spark plug wrench to remove the spark plug from the cylinder head.
- Reattach the Spark Plug Wire: Reattach the spark plug wire to the spark plug.
- Ground the Spark Plug: Hold the spark plug against a clean, unpainted metal surface on the engine block. This grounds the spark plug.
- Pull the Starter Cord: Pull the starter cord briskly.
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Observe the Spark: Observe the spark at the spark plug gap.
- Strong, Blue Spark: Indicates a healthy ignition coil and a good spark.
- Weak, Yellow Spark: Indicates a weak spark, which can be caused by a faulty ignition coil, a fouled spark plug, or a problem with the magneto.
- No Spark: Indicates a faulty ignition coil or another problem in the ignition system.
I once encountered a chainsaw that had a weak, intermittent spark. The resistance readings were within specification, but the spark test revealed the problem. Replacing the ignition coil with a new one restored the engine’s power and performance.
DIY vs. Professional Repair: Making the Right Choice
Testing and potentially replacing an ignition coil can be a rewarding DIY project. However, there are times when seeking professional help is the best course of action.
DIY is a Good Option If:
- You’re comfortable working on small engines.
- You have the necessary tools and equipment.
- You understand basic electrical concepts.
- You have access to a Stihl chainsaw service manual.
Seek Professional Help If:
- You’re uncomfortable with any step of the process.
- You’re not sure how to interpret the multimeter readings.
- You suspect a more complex problem with the ignition system.
- You don’t have the necessary tools or equipment.
Cost Considerations: Repair vs. Replacement
Before you decide to repair or replace your ignition coil, consider the cost implications.
- Ignition Coil Replacement: A new Stihl ignition coil can range in price from \$20 to \$100, depending on the model and the retailer.
- Professional Repair: The cost of professional repair can vary depending on the mechanic’s hourly rate and the complexity of the job.
In some cases, replacing the ignition coil yourself can be the most cost-effective option. However, if you’re unsure about the diagnosis or repair process, it’s always best to seek professional help to avoid further damage to your chainsaw.
Beyond the Ignition Coil: Other Potential Culprits
While the ignition coil is a common cause of starting problems, it’s essential to rule out other potential culprits:
- Spark Plug: A fouled or worn spark plug can prevent the engine from starting. Inspect the spark plug for signs of wear, carbon buildup, or damage. Replace the spark plug if necessary.
- Spark Plug Wire: A damaged or corroded spark plug wire can interrupt the flow of electricity to the spark plug. Inspect the spark plug wire for cracks, cuts, or corrosion. Replace the spark plug wire if necessary.
- Magneto: The magneto generates the electrical current that powers the ignition system. A faulty magneto can prevent the engine from starting. Test the magneto with a multimeter to check its output voltage.
- Fuel System: A clogged fuel filter, a malfunctioning carburetor, or stale fuel can prevent the engine from starting. Clean the fuel filter, rebuild the carburetor, or drain the fuel tank and refill it with fresh fuel.
- Compression: Low compression can prevent the engine from starting. Check the compression with a compression tester.
Conclusion: Keeping Your Stihl Chainsaw Roaring
Testing your Stihl ignition coil with a multimeter is a valuable skill that can save you time, money, and frustration. By following the steps outlined in this guide, you can confidently diagnose ignition coil problems and get your chainsaw back in action.
Remember to prioritize safety, use the right tools, and refer to your Stihl chainsaw service manual for specific instructions for your model. And if you’re ever unsure about any step of the process, don’t hesitate to seek professional help.
Now, armed with this knowledge, go forth and conquer those logs! Keep your chainsaw roaring, and your projects on track.
Next Steps:
- Gather your tools and materials.
- Review the safety precautions.
- Follow the step-by-step guide to test your Stihl ignition coil.
- Interpret the results and take appropriate action.
- If necessary, replace the ignition coil or seek professional help.
Happy cutting!
