How To Check A Coil Pack With Multimeter (3 Pro Arborist Tips)

Ever found yourself yanking the starter cord on your chainsaw, only to be met with stubborn silence? Or maybe it sputters and coughs but refuses to roar to life? The frustration is real, especially when you’re in the middle of a big firewood project or need to clear a fallen tree after a storm. One of the most common culprits behind these engine woes is a faulty coil pack, also known as an ignition coil. But how do you know for sure if that’s the problem? That’s where your trusty multimeter comes in.

Why Checking Your Coil Pack Matters: A Personal Story

Let me tell you a quick story. A few years back, I was hired to help clear a large property that had been hit hard by a microburst. Trees were down everywhere, and the homeowner was anxious to get things cleaned up. I brought my usual arsenal of chainsaws, including my trusty Stihl MS 261. On the second day, the 261 suddenly refused to start. I checked the fuel, the spark plug, everything seemed fine. I was about to call it a day when I remembered a similar issue I had faced with another saw.

I pulled out my multimeter and, sure enough, the coil pack was shot. Luckily, I had a spare in my truck (always be prepared!), and within minutes, I was back in business. The homeowner was amazed at how quickly I diagnosed and fixed the problem. That day, I learned the true value of knowing how to check a coil pack with a multimeter. It’s a skill that has saved me countless hours and kept my projects on track.

Understanding the Coil Pack: The Heart of Your Chainsaw’s Ignition System

Before we dive into the testing process, let’s take a moment to understand what a coil pack actually does. The coil pack, or ignition coil, is a crucial component of your chainsaw’s ignition system. Its primary function is to take the low-voltage electricity from the flywheel magneto and transform it into a high-voltage spark that ignites the air-fuel mixture in the cylinder. Without a properly functioning coil pack, your chainsaw simply won’t start or run correctly.

How a Coil Pack Works: A Simplified Explanation

Think of the coil pack as a tiny transformer. It consists of two coils of wire wrapped around an iron core:

Primary Coil: This coil has relatively few turns of thick wire. When the flywheel magneto spins, it generates a small amount of electricity in the primary coil.
Secondary Coil: This coil has thousands of turns of thin wire. The sudden interruption of the current in the primary coil induces a high-voltage current in the secondary coil.

This high-voltage current is then sent to the spark plug, creating the spark that ignites the fuel-air mixture.

Common Symptoms of a Faulty Coil Pack

Knowing the symptoms of a failing coil pack can help you diagnose the problem quickly. Here are some common signs to look for:

Chainsaw Won’t Start: This is the most obvious symptom. If the coil pack isn’t producing a strong enough spark, the engine won’t ignite.
Hard Starting: The chainsaw may start after multiple attempts, but it struggles to fire up.
Weak Spark: The spark plug may produce a weak or inconsistent spark.
Engine Misfires: The engine may run erratically, with occasional misfires or stalls.
Reduced Power: The chainsaw may lack power, especially when cutting through thicker wood.
Engine Stalling: The engine may stall frequently, especially when under load.

Safety First: Important Precautions Before Testing

Before you start testing your coil pack, it’s crucial to take some safety precautions:

Disconnect the Spark Plug: Always disconnect the spark plug wire from the spark plug before working on the ignition system. This prevents accidental starting and potential electrical shock.
Wear Gloves: Wear insulated gloves to protect yourself from electrical shock.
Work in a Well-Ventilated Area: Gasoline fumes are flammable and can be hazardous. Work in a well-ventilated area to avoid inhaling fumes.
Use the Right Tools: Use a multimeter that is designed for testing electrical components. Make sure the multimeter is in good working condition.
Read Your Chainsaw’s Manual: Consult your chainsaw’s manual for specific instructions and safety guidelines.

Pro Arborist Tip #1: Visual Inspection – The First Line of Defense

Before you even reach for your multimeter, give the coil pack a thorough visual inspection. This simple step can often reveal obvious problems that would otherwise be overlooked.

What to Look For During a Visual Inspection:

Cracks or Damage: Check the coil pack housing for any cracks, chips, or other signs of physical damage. Cracks can allow moisture to enter the coil pack, leading to corrosion and electrical shorts.
Corrosion: Look for signs of corrosion on the coil pack terminals and wiring. Corrosion can impede the flow of electricity and cause the coil pack to fail.
Loose Connections: Make sure all the wiring connections to the coil pack are secure and tight. Loose connections can cause intermittent sparking or a complete loss of spark.
Burn Marks: Check for any burn marks or discoloration on the coil pack. These can indicate overheating and internal damage.
Damaged Wiring: Inspect the wiring leading to and from the coil pack for any cuts, abrasions, or signs of damage. Damaged wiring can cause shorts or open circuits.

A Real-World Example: The Case of the Squirrel-Chewed Wire

I once had a chainsaw that wouldn’t start, and after a quick visual inspection, I discovered that a squirrel had chewed through one of the wires leading to the coil pack. The wire was almost completely severed, which was preventing the coil pack from receiving power. A simple wire repair saved me the time and expense of replacing the entire coil pack.

Why Visual Inspection is Important:

Saves Time: A visual inspection can often identify obvious problems quickly, saving you time and effort.
Prevents Misdiagnosis: By identifying physical damage, you can avoid misdiagnosing the problem as an internal electrical issue.
Reduces Costs: Repairing a loose connection or damaged wire is often much cheaper than replacing the entire coil pack.

Understanding Resistance: The Key to Coil Pack Testing

Before we start testing with the multimeter, it’s essential to understand the concept of resistance. Resistance is the opposition to the flow of electrical current. It’s measured in ohms (Ω). In the context of a coil pack, resistance tells us about the condition of the internal windings.

Why Resistance Matters:

Coil Pack Health: The resistance of the primary and secondary coils should fall within a specific range. If the resistance is too high or too low, it indicates a problem with the coil pack.
Short Circuits: Low resistance can indicate a short circuit within the coil pack.
Open Circuits: High resistance or infinite resistance can indicate an open circuit, meaning the wire is broken.

Using the Multimeter to Measure Resistance:

A multimeter can measure resistance. Here’s how:

Set the Multimeter: Turn the multimeter to the ohms (Ω) setting. You may need to select the appropriate range, depending on the multimeter. Start with a higher range and work your way down until you get a stable reading.
Touch the Probes: Touch the multimeter probes together. The reading should be close to zero, indicating that the multimeter is working correctly.
Connect to the Coil Pack: Connect the multimeter probes to the appropriate terminals on the coil pack.
Read the Resistance: Read the resistance value displayed on the multimeter.
Compare to Specifications: Compare the measured resistance to the specifications in your chainsaw’s manual or a reliable online resource.

Pro Arborist Tip #2: Testing Primary and Secondary Coil Resistance – The Core Diagnostic Test

Now we get to the heart of the matter: testing the resistance of the primary and secondary coils. This is the most important test for determining if your coil pack is functioning correctly.

Step-by-Step Guide to Testing Primary Coil Resistance:

Locate the Primary Terminals: Identify the primary terminals on the coil pack. These are typically the two smaller terminals that connect to the ignition module or wiring harness.
Set the Multimeter: Turn the multimeter to the ohms (Ω) setting, typically in the range of 200 ohms.
Connect the Probes: Connect one multimeter probe to each of the primary terminals.
Read the Resistance: Read the resistance value displayed on the multimeter.
Compare to Specifications: Compare the measured resistance to the specifications in your chainsaw’s manual or a reliable online resource. The primary coil resistance is usually quite low, often less than 1 ohm to around 5 ohms.

Example: Let’s say your chainsaw’s manual specifies a primary coil resistance of 0.5 to 2.0 ohms. If your multimeter reads 0.8 ohms, the primary coil is likely within the acceptable range. However, if it reads 0.1 ohms or 5.0 ohms, there’s likely a problem.

Step-by-Step Guide to Testing Secondary Coil Resistance:

Locate the Secondary Terminals: Identify the secondary terminals on the coil pack. One terminal is typically the spark plug wire connection, and the other is a ground connection.
Set the Multimeter: Turn the multimeter to the ohms (Ω) setting, typically in the range of 20,000 ohms (20kΩ).
Connect the Probes: Connect one multimeter probe to the spark plug wire connection and the other probe to the ground connection.
Read the Resistance: Read the resistance value displayed on the multimeter.
Compare to Specifications: Compare the measured resistance to the specifications in your chainsaw’s manual or a reliable online resource. The secondary coil resistance is typically much higher than the primary coil resistance, often ranging from 2,000 to 10,000 ohms.

Example: Let’s say your chainsaw’s manual specifies a secondary coil resistance of 4,000 to 8,000 ohms. If your multimeter reads 5,500 ohms, the secondary coil is likely within the acceptable range. However, if it reads 1,000 ohms or 12,000 ohms, there’s likely a problem.

Interpreting the Results: What the Resistance Readings Mean

Resistance Too Low: This could indicate a short circuit within the coil pack. A short circuit can cause the coil pack to overheat and fail.
Resistance Too High: This could indicate an open circuit or a break in the wiring within the coil pack. An open circuit will prevent the coil pack from producing a spark.
Infinite Resistance: This also indicates an open circuit. The multimeter will display “OL” or “1” on the screen, indicating that the resistance is too high to measure.
Resistance Within Specifications: If the resistance readings are within the specified range, the coil pack is likely functioning correctly. However, it’s still possible that the coil pack is failing under load.

Dealing with No Specifications: A Practical Approach

Sometimes, finding the exact resistance specifications for your specific chainsaw model can be tricky. Here’s what I do when faced with this situation:

Consult Online Forums: Search online forums dedicated to chainsaw repair. Other users may have encountered the same issue and shared the specifications for your model.
Check Similar Models: Look for specifications for similar chainsaw models from the same manufacturer. Coil pack resistance values are often similar across different models.
Use a Known Good Coil Pack: If you have access to a known good coil pack from the same model, measure its resistance and use those values as a benchmark.
Look for General Guidelines: In general, primary coil resistance should be very low (less than 5 ohms), and secondary coil resistance should be in the thousands of ohms (2,000 to 10,000 ohms).
When in Doubt, Replace: If you’re unsure about the resistance readings and the chainsaw is still not starting, it’s often best to replace the coil pack. Coil packs are relatively inexpensive, and replacing it can eliminate a major potential problem.

A Word of Caution: Temperature Sensitivity

Keep in mind that coil packs are sensitive to temperature. Resistance readings can vary depending on the temperature of the coil pack. It’s best to test the coil pack at room temperature for the most accurate results.

Pro Arborist Tip #3: The Spark Test – Confirming the Spark

Even if the resistance readings are within specifications, it’s still possible that the coil pack is not producing a strong enough spark to ignite the fuel-air mixture. That’s why it’s important to perform a spark test.

How to Perform a Spark Test:

Reconnect the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
Ground the Spark Plug: Hold the spark plug against a metal part of the engine, such as the cylinder head. This will ground the spark plug.
Pull the Starter Cord: Pull the starter cord quickly and repeatedly.
Observe the Spark: Observe the spark at the spark plug gap. The spark should be strong, blue, and consistent.

Interpreting the Spark Test Results:

Strong, Blue Spark: This indicates that the coil pack is likely functioning correctly.
Weak, Yellow Spark: This indicates that the coil pack is producing a weak spark, which may not be strong enough to ignite the fuel-air mixture.
No Spark: This indicates that the coil pack is not producing any spark at all.

Common Problems That Can Affect the Spark:

Fouled Spark Plug: A fouled spark plug can prevent the spark from jumping the gap. Clean or replace the spark plug.
Incorrect Spark Plug Gap: An incorrect spark plug gap can also affect the spark. Adjust the spark plug gap to the specifications in your chainsaw’s manual.
Damaged Spark Plug Wire: A damaged spark plug wire can cause a weak or intermittent spark. Replace the spark plug wire.
Poor Ground Connection: A poor ground connection can prevent the spark from jumping the gap. Make sure the spark plug is properly grounded to the engine.

Enhancing Spark Visibility: A Trick I Learned

Sometimes, it’s hard to see the spark, especially in bright daylight. Here’s a trick I learned from an old-timer:

Find a Dark Area: Move the chainsaw to a shaded area or wait until dusk.
Create a Shield: Cup your hands around the spark plug to block out any ambient light.
Look Closely: Look closely at the spark plug gap while pulling the starter cord. Even a weak spark will be more visible in the dark.

When the Spark Test Fails: Next Steps

If the spark test fails, and you’ve already checked the spark plug, spark plug wire, and ground connection, then the coil pack is likely the problem. It’s time to replace the coil pack.

Replacing the Coil Pack: A Step-by-Step Guide

Replacing a coil pack is a relatively straightforward process. Here’s a step-by-step guide:

Gather Your Tools: You’ll need a screwdriver, a socket set, and a new coil pack.
Disconnect the Spark Plug Wire: Disconnect the spark plug wire from the spark plug.
Remove the Engine Cover: Remove the engine cover to access the coil pack.
Disconnect the Wiring: Disconnect the wiring from the coil pack.
Remove the Old Coil Pack: Remove the screws or bolts that hold the coil pack in place.
Install the New Coil Pack: Install the new coil pack, making sure it’s properly aligned.
Connect the Wiring: Connect the wiring to the new coil pack.
Reinstall the Engine Cover: Reinstall the engine cover.
Reconnect the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
Adjust the Air Gap: Some coil packs require you to adjust the air gap between the coil pack and the flywheel. Use a business card or a feeler gauge to set the correct gap. Consult your chainsaw’s manual for the correct gap specification.

Setting the Air Gap: Why It’s Crucial

The air gap is the distance between the coil pack and the flywheel. This gap is crucial for proper ignition timing. If the air gap is too large, the spark will be weak. If the air gap is too small, the coil pack can rub against the flywheel and become damaged.

A Common Mistake: Forgetting the Air Gap

One of the most common mistakes people make when replacing a coil pack is forgetting to set the air gap. I’ve seen countless instances where someone replaces the coil pack, only to find that the chainsaw still won’t start. In most cases, the problem is simply that the air gap is not set correctly.

Aftermarket vs. OEM Coil Packs: Making the Right Choice

When replacing a coil pack, you’ll have the option of choosing between an aftermarket coil pack and an OEM (Original Equipment Manufacturer) coil pack. Here’s a quick comparison:

OEM Coil Packs: These are manufactured by the same company that made your chainsaw. They are typically more expensive but are guaranteed to fit and function correctly.
Aftermarket Coil Packs: These are manufactured by third-party companies. They are typically less expensive but may not be as reliable as OEM coil packs.

In general, I recommend using an OEM coil pack whenever possible. While aftermarket coil packs can save you money in the short term, they may not last as long or perform as well as OEM coil packs.

Budget-Friendly Tip: Refurbishing a Coil Pack (Proceed with Caution!)

While not generally recommended, in a pinch, you might be able to temporarily refurbish a coil pack if the issue is simply corrosion on the terminals. Clean the terminals with a wire brush or sandpaper to remove any corrosion. Apply a small amount of dielectric grease to the terminals to prevent future corrosion. However, keep in mind that this is only a temporary fix. If the coil pack is internally damaged, it will eventually need to be replaced. This is really a ‘get you home’ fix only.

Beyond the Coil Pack: Other Ignition System Components

While the coil pack is a common culprit, it’s important to remember that it’s just one component of the ignition system. Other components that can cause ignition problems include:

Spark Plug: A fouled, damaged, or incorrectly gapped spark plug can prevent the engine from starting.
Spark Plug Wire: A damaged spark plug wire can cause a weak or intermittent spark.
Flywheel Magneto: The flywheel magneto generates the electricity that powers the ignition system. A weak or damaged magneto can prevent the coil pack from producing a spark.
Ignition Module: The ignition module controls the timing of the spark. A faulty ignition module can cause the engine to misfire or not start at all.
Kill Switch: A faulty kill switch can prevent the engine from starting.

Diagnosing Other Ignition System Problems:

Spark Plug: Check the spark plug for fouling, damage, or incorrect gap. Clean or replace the spark plug as needed.
Spark Plug Wire: Check the spark plug wire for damage. Replace the spark plug wire if necessary.
Flywheel Magneto: Use a multimeter to test the output voltage of the flywheel magneto. Consult your chainsaw’s manual for the correct voltage specification.
Ignition Module: Testing the ignition module can be more complex and may require specialized tools. Consult your chainsaw’s manual or a qualified mechanic.
Kill Switch: Disconnect the kill switch wire from the ignition module. If the chainsaw starts, the kill switch is faulty.

Maintaining Your Chainsaw’s Ignition System: Prevention is Key

The best way to avoid coil pack problems is to maintain your chainsaw’s ignition system properly. Here are some tips:

Use Fresh Fuel: Always use fresh, high-quality fuel. Old or contaminated fuel can damage the ignition system.
Maintain the Spark Plug: Clean or replace the spark plug regularly. Follow the manufacturer’s recommendations for spark plug maintenance.
Store Your Chainsaw Properly: Store your chainsaw in a dry, clean place. Moisture and dirt can damage the ignition system.
Inspect the Wiring: Regularly inspect the wiring for damage. Repair or replace any damaged wiring.
Keep the Engine Clean: Keep the engine clean to prevent overheating. Overheating can damage the coil pack.

Fuel Stabilizers: A Must-Have for Chainsaw Owners

Fuel stabilizers are additives that help prevent fuel from breaking down and forming harmful deposits. Using a fuel stabilizer can significantly extend the life of your chainsaw’s ignition system. I recommend adding a fuel stabilizer to your fuel every time you fill up the gas can, especially if you don’t use your chainsaw frequently.

Regular Maintenance Schedule: A Proactive Approach

Creating a regular maintenance schedule can help you catch potential problems before they become major issues. Here’s a sample maintenance schedule:

Every Use: Check the spark plug for fouling, damage, or incorrect gap. Clean or replace the spark plug as needed.
Monthly: Inspect the wiring for damage. Repair or replace any damaged wiring.
Annually: Replace the spark plug. Inspect the flywheel magneto and ignition module.

Troubleshooting Checklist: A Quick Reference Guide

Here’s a quick troubleshooting checklist to help you diagnose and fix coil pack problems:

Chainsaw Won’t Start:
- Check the fuel level.
- Check the spark plug for fouling, damage, or incorrect gap.
- Perform a visual inspection of the coil pack.
- Test the primary and secondary coil resistance.
- Perform a spark test.
- Replace the coil pack if necessary.
Engine Misfires:
- Check the spark plug for fouling, damage, or incorrect gap.
- Check the spark plug wire for damage.
- Test the primary and secondary coil resistance.
- Perform a spark test.
- Replace the coil pack if necessary.
Reduced Power:
- Check the spark plug for fouling, damage, or incorrect gap.
- Test the primary and secondary coil resistance.
- Perform a spark test.
- Replace the coil pack if necessary.

Conclusion: Mastering the Coil Pack Check for Chainsaw Longevity

Checking a coil pack with a multimeter is a valuable skill for anyone who owns a chainsaw or other small engine equipment. By following the steps outlined in this guide, you can quickly and accurately diagnose coil pack problems and save yourself time, money, and frustration. Remember to always prioritize safety and consult your chainsaw’s manual for specific instructions and safety guidelines.

Don’t be intimidated by the technical jargon or the complexity of the ignition system. With a little practice and patience, you can become a master of coil pack checking and keep your chainsaw running smoothly for years to come. And remember, a well-maintained chainsaw is not only more reliable but also safer to use. So, take the time to learn about your equipment and keep it in good working condition. Your hard work will pay off in the long run.

Now, go forth and conquer those wood piles! You’ve got the knowledge and the tools to keep your chainsaw roaring.