How To Test A Coil With An Ohmmeter (Chainsaw Tune-Up Tips)

Aha! It hit me like a rogue branch to the face – the sputtering chainsaw, the frustration, the wasted time… all pointing to one culprit: a faulty ignition coil. I remember vividly that crisp autumn morning, ready to tackle a mountain of firewood, only to be defeated by a stubborn engine. That’s when I realized, understanding how to test a coil with an ohmmeter wasn’t just a useful skill; it was the key to keeping my chainsaw humming and my woodpile growing.

This isn’t just about fixing a chainsaw; it’s about self-sufficiency, saving money, and the satisfaction of knowing you can handle whatever challenges the woodlot throws your way. So, grab your ohmmeter, and let’s dive into the world of chainsaw ignition coils. I’m going to walk you through everything you need to know, from understanding the basics of ignition systems to performing the tests that will pinpoint whether your coil is the problem. Think of me as your guide through the tangled underbrush of chainsaw mechanics.

Chainsaw Tune-Up Tips: How to Test a Coil with an Ohmmeter

Understanding the Chainsaw Ignition System: The Spark of Life

Before we get our hands dirty with the ohmmeter, let’s understand the role of the ignition coil within the larger chainsaw ignition system. It’s the heart of the electrical system, responsible for generating the high-voltage spark that ignites the fuel-air mixture in the cylinder. Without a properly functioning coil, you’re essentially trying to start a fire without a match.

The typical chainsaw ignition system consists of these key components:

Flywheel: A rotating component with magnets embedded in it. As the flywheel spins, these magnets pass by the ignition coil.
Ignition Coil: Also known as the armature, this device uses the changing magnetic field from the flywheel to induce a high-voltage current.
Spark Plug: The final destination of the high-voltage current. The spark plug creates a spark gap within the cylinder, igniting the fuel-air mixture.
Ignition Module (Sometimes): Some newer chainsaws use an electronic ignition module to control the timing and strength of the spark.
Kill Switch: A simple switch that grounds the ignition system, preventing the spark plug from firing and stopping the engine.

The magic happens through electromagnetic induction. As the flywheel’s magnets rapidly pass the ignition coil, they create a changing magnetic field. This changing field induces a voltage in the coil’s primary winding. The coil then uses a transformer-like action to step up this voltage to thousands of volts in the secondary winding. This high voltage then travels to the spark plug, creating the spark that starts the combustion process.

Why Coils Fail: The Usual Suspects

Ignition coils, like any mechanical component, are prone to failure. Here’s a rundown of the common culprits:

Heat: Chainsaws operate in demanding environments, and the engine heat can take a toll on the coil’s insulation, leading to shorts and failures.
Vibration: The constant vibration of a chainsaw can weaken the coil’s internal connections and cause components to break down.
Moisture: Exposure to moisture can corrode the coil’s terminals and windings, leading to poor performance or complete failure.
Age: Over time, the insulation on the coil’s windings can degrade, leading to shorts and reduced output.
Physical Damage: Impacts or mishandling can physically damage the coil, rendering it useless.

Symptoms of a Faulty Ignition Coil: Recognizing the Warning Signs

Recognizing the symptoms of a failing ignition coil can save you time and frustration. Here are some telltale signs:

Hard Starting: The engine is difficult to start, requiring excessive pulling or cranking.
No Starting: The engine refuses to start at all, even after repeated attempts.
Weak Spark: The spark at the spark plug is weak or intermittent. This can be difficult to see with the naked eye, but you might notice a faint or yellowish spark instead of a strong blue one.
Misfiring: The engine runs erratically, with occasional misfires or stalls.
Poor Performance: The engine lacks power and struggles to maintain speed, especially under load.
Engine Stalling: The engine stalls frequently, especially when hot.

If you experience any of these symptoms, testing the ignition coil is a crucial step in diagnosing the problem.

Preparing for the Test: Gathering Your Tools and Knowledge

Before you dive into testing, make sure you have the right tools and a clear understanding of the process.

Ohmmeter (Multimeter): A digital multimeter is ideal for this task. Ensure it’s in good working order and the battery is fresh. Analog multimeters can also be used, but digital meters are generally more accurate and easier to read. You’ll want to make sure your ohmmeter is capable of measuring low resistances (less than 1 ohm) and high resistances (several thousand ohms).
Chainsaw Service Manual (Recommended): Your chainsaw’s service manual is invaluable. It provides specific resistance values for your particular coil model. These values are crucial for accurate testing. If you don’t have a physical manual, you can often find them online through the manufacturer’s website or online forums.
Safety Glasses: Protect your eyes from debris and potential sparks.
Gloves: Protect your hands from dirt, grease, and potential electrical shocks (although the voltage is low, it’s always best to be cautious).
Screwdrivers and Wrenches: You’ll need these to access the ignition coil. Refer to your chainsaw’s service manual for the specific tools required.
Cleaning Supplies: A clean rag and some electrical contact cleaner can help ensure accurate readings.
A Clean, Well-Lit Work Area: This will make the process easier and safer.

Safety First: Important Precautions

Working with electrical components requires caution. Here are some important safety precautions to keep in mind:

Disconnect the Spark Plug Wire: Always disconnect the spark plug wire from the spark plug before working on the ignition system. This prevents accidental starting and potential electrical shock.
Allow the Engine to Cool: Let the engine cool down completely before working on it. This prevents burns from hot engine components.
Work in a Well-Ventilated Area: If you’re using any cleaning solvents or sprays, work in a well-ventilated area to avoid inhaling harmful fumes.
Follow the Manufacturer’s Instructions: Always refer to your chainsaw’s service manual for specific safety instructions and procedures.
If in Doubt, Seek Professional Help: If you’re uncomfortable performing any of these tests, consult a qualified chainsaw mechanic.

Testing the Ignition Coil: A Step-by-Step Guide

Now, let’s get to the heart of the matter: testing the ignition coil with an ohmmeter. This involves measuring the resistance of the primary and secondary windings of the coil. The resistance values should fall within the specifications outlined in your chainsaw’s service manual.

Step 1: Accessing the Ignition Coil

The first step is to access the ignition coil. This typically involves removing the chainsaw’s engine cover and possibly some other components. Refer to your chainsaw’s service manual for specific instructions.

Remove the Engine Cover: Use the appropriate screwdrivers or wrenches to remove the engine cover.
Locate the Ignition Coil: The ignition coil is usually located near the flywheel. It’s a small, rectangular component with wires leading to the spark plug and other parts of the ignition system.
Disconnect the Wires: Carefully disconnect the wires from the ignition coil. Make sure to note the position of each wire so you can reconnect them correctly later. It’s a good idea to take a picture with your phone before disconnecting anything.

Step 2: Testing the Primary Winding

The primary winding is the low-voltage side of the coil. It’s typically connected to the ignition module or points system.

Set the Ohmmeter: Set your ohmmeter to the lowest resistance scale (usually in the ohms range).
Connect the Probes: Touch the ohmmeter probes to the two terminals of the primary winding. These terminals are usually clearly marked or identifiable by their smaller size.
Read the Resistance: Read the resistance value displayed on the ohmmeter.
Compare to Specifications: Compare the measured resistance value to the specifications in your chainsaw’s service manual. The primary winding resistance is typically very low, often less than 1 ohm.

Interpreting the Results for the Primary Winding:

Resistance within Specifications: If the measured resistance is within the specified range, the primary winding is likely good.
Zero Resistance (Short Circuit): If the ohmmeter reads zero resistance, it indicates a short circuit in the primary winding. This means the coil is likely faulty and needs to be replaced.
Infinite Resistance (Open Circuit): If the ohmmeter reads infinite resistance (or “OL” for “Over Limit”), it indicates an open circuit in the primary winding. This also means the coil is likely faulty and needs to be replaced.
Resistance Significantly Outside Specifications: If the resistance is significantly higher or lower than the specified range, it indicates a problem with the primary winding. The coil is likely faulty and needs to be replaced.

Step 3: Testing the Secondary Winding

The secondary winding is the high-voltage side of the coil. It’s connected to the spark plug.

Set the Ohmmeter: Set your ohmmeter to a higher resistance scale (usually in the kilohms or thousands of ohms range).
Connect the Probes: Connect one ohmmeter probe to the spark plug wire terminal (where the spark plug wire connects to the coil) and the other probe to the coil’s ground terminal (usually the metal mounting bracket).
Read the Resistance: Read the resistance value displayed on the ohmmeter.
Compare to Specifications: Compare the measured resistance value to the specifications in your chainsaw’s service manual. The secondary winding resistance is typically much higher than the primary winding resistance, often in the range of 2,000 to 10,000 ohms.

Interpreting the Results for the Secondary Winding:

Resistance within Specifications: If the measured resistance is within the specified range, the secondary winding is likely good.
Zero Resistance (Short Circuit): If the ohmmeter reads zero resistance, it indicates a short circuit in the secondary winding. This means the coil is likely faulty and needs to be replaced.
Infinite Resistance (Open Circuit): If the ohmmeter reads infinite resistance (or “OL” for “Over Limit”), it indicates an open circuit in the secondary winding. This also means the coil is likely faulty and needs to be replaced.
Resistance Significantly Outside Specifications: If the resistance is significantly higher or lower than the specified range, it indicates a problem with the secondary winding. The coil is likely faulty and needs to be replaced.

Step 4: Checking for Grounding Issues

In addition to testing the primary and secondary windings, it’s also important to check for grounding issues. This involves testing the resistance between the coil’s terminals and the coil’s metal mounting bracket (which should be grounded to the engine).

Set the Ohmmeter: Set your ohmmeter to the highest resistance scale (usually in the megohms or millions of ohms range).
Connect the Probes: Connect one ohmmeter probe to one of the coil’s terminals (either primary or secondary) and the other probe to the coil’s metal mounting bracket.
Read the Resistance: Read the resistance value displayed on the ohmmeter.
Interpret the Results: The resistance should be very high (ideally infinite or “OL”). A low resistance reading indicates a grounding issue, which means the coil is shorting to ground. This can cause weak spark or no spark at all. If you find a grounding issue, the coil needs to be replaced.

Step 5: Reassembly and Testing

If your coil passes all the tests, it’s likely in good working order. However, it’s still a good idea to double-check your connections and test the chainsaw before putting everything back together.

Reconnect the Wires: Carefully reconnect the wires to the ignition coil, making sure to connect them in the correct positions. Refer to the picture you took earlier if needed.
Reinstall the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
Test the Chainsaw: Try starting the chainsaw. If it starts and runs smoothly, the ignition coil is likely not the problem. If it still doesn’t start or runs poorly, there may be other issues with the ignition system or fuel system.
Reinstall the Engine Cover: If the chainsaw is running properly, reinstall the engine cover and any other components you removed.

Beyond the Ohmmeter: Other Diagnostic Tips

While the ohmmeter test is a valuable tool, it’s not always definitive. Here are some other diagnostic tips to consider:

Visual Inspection: Carefully inspect the ignition coil for any signs of physical damage, such as cracks, burns, or corrosion.
Spark Test: Remove the spark plug, connect it to the spark plug wire, and ground the spark plug against the engine. Pull the starter cord and observe the spark. A strong, blue spark indicates a healthy ignition system. A weak, yellow spark or no spark indicates a problem. Note that some electronic ignition systems require the spark plug to be under compression to produce a spark.
Air Gap Adjustment: The air gap between the flywheel and the ignition coil is critical for proper operation. Refer to your chainsaw’s service manual for the correct air gap specification. Use a feeler gauge to adjust the air gap as needed. A business card folded in half often works in a pinch.
Spark Plug Condition: Inspect the spark plug for signs of fouling, damage, or wear. A fouled or damaged spark plug can cause starting problems and poor performance. Replace the spark plug if necessary.
Fuel System Check: Make sure the fuel tank is full of fresh fuel and that the fuel filter is clean. A clogged fuel filter can restrict fuel flow and cause starting problems and poor performance.
Carburetor Adjustment: A poorly adjusted carburetor can also cause starting problems and poor performance. Refer to your chainsaw’s service manual for instructions on how to adjust the carburetor.

When to Replace the Ignition Coil: Making the Call

After performing the ohmmeter test and other diagnostic checks, you may need to decide whether to replace the ignition coil. Here are some guidelines:

Failed Ohmmeter Test: If the ohmmeter test indicates a short circuit, open circuit, or grounding issue, the coil needs to be replaced.
Visible Damage: If the coil shows signs of physical damage, such as cracks, burns, or corrosion, it should be replaced.
Weak Spark: If the spark test reveals a weak or intermittent spark, and other components (such as the spark plug) are in good condition, the coil may need to be replaced.
Persistent Starting Problems: If you’ve tried all the other diagnostic checks and the chainsaw still has persistent starting problems, the coil may be the culprit.

Choosing a Replacement Coil: Quality Matters

When replacing the ignition coil, it’s important to choose a quality replacement part. Here are some tips:

OEM vs. Aftermarket: OEM (Original Equipment Manufacturer) coils are generally the highest quality, but they can also be the most expensive. Aftermarket coils can be a more affordable option, but it’s important to choose a reputable brand.
Compatibility: Make sure the replacement coil is compatible with your chainsaw model. Check the part number in your chainsaw’s service manual or online parts catalog.
Warranty: Look for a replacement coil that comes with a warranty. This will protect you in case the coil fails prematurely.
Reviews: Read online reviews of different replacement coils to get an idea of their quality and reliability.

Installing the New Coil: A Detailed Guide

Installing a new ignition coil is a straightforward process, but it’s important to follow the instructions carefully.

Disconnect the Spark Plug Wire: Always disconnect the spark plug wire from the spark plug before working on the ignition system.
Remove the Old Coil: Remove the old ignition coil by unscrewing the mounting screws and disconnecting the wires.
Install the New Coil: Install the new ignition coil in the same position as the old one. Tighten the mounting screws securely.
Connect the Wires: Connect the wires to the new ignition coil, making sure to connect them in the correct positions. Refer to the picture you took earlier if needed.
Adjust the Air Gap: Adjust the air gap between the flywheel and the ignition coil. Refer to your chainsaw’s service manual for the correct air gap specification. Use a feeler gauge to adjust the air gap as needed.
Reconnect the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
Test the Chainsaw: Try starting the chainsaw. If it starts and runs smoothly, the new ignition coil is working properly.
Reinstall the Engine Cover: If the chainsaw is running properly, reinstall the engine cover and any other components you removed.

Maintaining Your Ignition Coil: Prevention is Key

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

Keep the Engine Clean: Keep the engine clean and free of debris. This will help prevent overheating and corrosion.
Check the Air Gap Regularly: Check the air gap between the flywheel and the ignition coil regularly. Adjust the air gap as needed.
Use Fresh Fuel: Use fresh, high-quality fuel. Old or contaminated fuel can damage the engine and ignition system.
Store the Chainsaw Properly: Store the chainsaw in a dry, protected location. This will help prevent moisture and corrosion.
Follow the Manufacturer’s Recommendations: Follow the manufacturer’s recommendations for maintenance and service.

Wood Science Insights: The Impact of Wood Moisture on Chainsaw Performance

Now, let’s shift gears a bit and delve into the fascinating world of wood science. The moisture content of the wood you’re cutting can significantly impact your chainsaw’s performance and the overall strain on its components, including the ignition system.

Wet Wood vs. Dry Wood: Cutting wet wood requires more power than cutting dry wood. This is because wet wood is denser and more difficult to cut through. The increased resistance can put a strain on the engine, potentially leading to overheating and ignition system problems.
Moisture Content and Cutting Efficiency: The ideal moisture content for cutting most types of wood is between 20% and 30%. This allows for efficient cutting without excessive strain on the chainsaw.
Using a Moisture Meter: A moisture meter can help you determine the moisture content of the wood you’re cutting. This can help you adjust your cutting technique and choose the right chainsaw for the job.
Seasoning Firewood: Seasoning firewood reduces its moisture content, making it easier to cut and burn. Properly seasoned firewood also produces more heat and less smoke. I’ve always found a good rule of thumb is to season hardwoods for at least a year, and softwoods for at least six months, in a well-ventilated area.

Logging Tool Selection: Matching the Tool to the Task

Choosing the right logging tool for the job is essential for safety, efficiency, and preventing unnecessary wear and tear on your equipment. This includes selecting the right chainsaw for the type of wood you’re cutting.

Chainsaw Size and Power: Choose a chainsaw with the appropriate size and power for the type of wood you’re cutting. A small, lightweight chainsaw is suitable for limbing and cutting small branches, while a larger, more powerful chainsaw is needed for felling trees and cutting large logs.
Bar Length: Choose a bar length that is appropriate for the diameter of the wood you’re cutting. The bar length should be at least as long as the diameter of the wood.
Chain Type: Choose the right type of chain for the type of wood you’re cutting. Different chain types are designed for different cutting applications, such as ripping, crosscutting, and boring.
Personal Protective Equipment (PPE): Always wear appropriate PPE when operating a chainsaw, including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps.

Firewood Seasoning Techniques: Maximizing Fuel Value

Proper firewood seasoning is crucial for maximizing its fuel value and minimizing smoke production. Here are some effective seasoning techniques:

Stacking Method: Stack the firewood in a single row, with the bark side up. This allows for better air circulation and faster drying.
Location: Stack the firewood in a sunny, well-ventilated location. This will help speed up the drying process.
Elevation: Elevate the firewood off the ground using pallets or timbers. This will prevent moisture from wicking up from the ground.
Covering: Cover the top of the firewood pile with a tarp or roof to protect it from rain and snow.
Drying Time: Allow the firewood to dry for at least six months, or preferably a year. The longer it dries, the better it will burn.

Project Planning and Execution: A Holistic Approach

Planning and executing your wood processing projects efficiently can save you time, money, and frustration. Here’s a holistic approach to consider:

Assess Your Needs: Determine how much firewood you need for the winter.
Source Your Wood: Find a reliable source of firewood, such as a local firewood dealer or a private landowner.
Plan Your Cuts: Plan your cuts carefully to maximize the yield and minimize waste.
Work Safely: Always prioritize safety when working with chainsaws and other logging tools.
Store Your Firewood Properly: Store your firewood in a dry, protected location.

Data Points and Statistics: The Numbers Behind Wood Processing

Let’s add some data-backed insights to further illustrate the importance of efficient wood processing:

Fuel Value of Dry Wood: Dry firewood has a significantly higher fuel value than wet firewood. For example, dry oak firewood can produce up to 20 million BTUs per cord, while wet oak firewood may only produce 10 million BTUs per cord.
Cost Savings of Seasoning Firewood: Seasoning your own firewood can save you a significant amount of money compared to buying pre-seasoned firewood. The exact amount will vary depending on your location and the price of firewood.
Efficiency of Hydraulic Splitters: Hydraulic log splitters can significantly increase the efficiency of firewood splitting compared to manual splitting. A hydraulic splitter can split a cord of firewood in a few hours, while it may take several days to split a cord of firewood manually.
Statistics on Chainsaw Injuries: According to the Consumer Product Safety Commission, there are approximately 30,000 chainsaw-related injuries in the United States each year. Wearing appropriate PPE and following safety precautions can significantly reduce the risk of injury.

Real-World Examples and Case Studies: Learning from Experience

I’ve seen firsthand how these principles play out in real-world scenarios.

Case Study 1: The Overheated Chainsaw: A friend of mine was cutting wet wood all day long with a small chainsaw. The engine overheated, and the ignition coil failed. By switching to a larger chainsaw and allowing the engine to cool down periodically, he was able to avoid further problems.
Case Study 2: The Poorly Seasoned Firewood: A neighbor of mine tried to burn firewood that had only been seasoned for a few weeks. The firewood was difficult to light, produced a lot of smoke, and didn’t generate much heat. By seasoning the firewood for a full year, he was able to burn it efficiently and cleanly.
My Own Experience: The Faulty Coil Discovery: As I mentioned at the beginning, my own experience with a faulty ignition coil taught me the importance of understanding chainsaw mechanics and being able to diagnose problems myself. It saved me time and money, and it gave me a sense of accomplishment.

Practical Tips and Actionable Advice: Putting Knowledge into Practice

Here are some practical tips and actionable advice you can apply immediately:

Test Your Ignition Coil Regularly: Test your ignition coil at least once a year, or more often if you suspect a problem.
Keep Your Chainsaw Clean: Clean your chainsaw regularly to prevent overheating and corrosion.
Use Fresh Fuel: Use fresh, high-quality fuel to ensure optimal performance.
Season Your Firewood Properly: Season your firewood for at least six months, or preferably a year.
Wear Appropriate PPE: Always wear appropriate PPE when operating a chainsaw.

Challenges Faced by Small Workshops and DIYers Globally

These challenges can include:

Limited Resources: Small workshops and DIYers often have limited access to resources, such as tools, equipment, and training.
Budget Constraints: Budget constraints can make it difficult to purchase high-quality tools and equipment.
Lack of Space: Limited space can make it difficult to store firewood and other materials.
Climate Conditions: Climate conditions can affect the drying time of firewood and the performance of chainsaws.
Access to Information: Access to accurate and reliable information can be limited, especially in remote areas.

Despite these challenges, small workshops and DIYers can still achieve success by being resourceful, creative, and committed to safety.

Conclusion: Takeaways and Next Steps

Testing your chainsaw’s ignition coil with an ohmmeter is a valuable skill that can save you time, money, and frustration. By understanding the basics of the ignition system, recognizing the symptoms of a faulty coil, and following the steps outlined in this article, you can diagnose and fix ignition problems yourself. Remember to prioritize safety, use quality replacement parts, and maintain your chainsaw properly.

Here are some key takeaways:

The ignition coil is a critical component of the chainsaw’s ignition system.
A faulty ignition coil can cause starting problems, poor performance, and engine stalling.
Testing the ignition coil with an ohmmeter can help you diagnose ignition problems.
Proper maintenance can help extend the life of your ignition coil.
Always prioritize safety when working with chainsaws and other logging tools.

Now that you have the knowledge and tools, take the next step and test your chainsaw’s ignition coil. If you find a problem, replace the coil and get back to cutting wood! And remember, the satisfaction of fixing something yourself is a reward in itself. So, go forth, conquer those logs, and keep your woodpile growing!