How to Test Ignition Coil Pack with Multimeter (Chainsaw Repair Tips)
Aha! There I was, knee-deep in sawdust, wrestling with a chainsaw that coughed and sputtered like a disgruntled dragon. I’d spent the morning felling a beautiful oak, envisioning stacks of seasoned firewood warming homes through the winter. But my trusty saw, usually a roaring beast of burden, had decided to stage a mutiny. After checking the fuel, the spark plug, and muttering a few choice words (as any seasoned woodcutter would), the problem became glaringly obvious: the ignition coil pack. That’s when the “aha” moment hit. Knowing how to test this little component could save me hours of frustration and a trip to the repair shop. And that’s exactly what I’m going to share with you today.
So, you’re facing a similar chainsaw conundrum? Your saw’s acting up, and you suspect the ignition coil pack might be the culprit? You’ve come to the right place. I’m going to walk you through the process of testing your chainsaw’s ignition coil pack with a multimeter, step-by-step. But before we dive into the nitty-gritty, let’s understand why this little part is so important and what makes it fail.
The Ignition Coil Pack: The Heart of Your Chainsaw’s Spark
Think of the ignition coil pack as the heart of your chainsaw’s electrical system. It takes the low-voltage current from the magneto (a small generator powered by the engine’s flywheel) and transforms it into the high-voltage jolt needed to create a spark at the spark plug. This spark ignites the fuel-air mixture in the cylinder, creating the combustion that drives the piston and, ultimately, the chain. Without a functioning ignition coil pack, your chainsaw is nothing more than a heavy, noisy paperweight.
Common Reasons for Ignition Coil Pack Failure
Ignition coil packs are surprisingly robust, but they’re not immune to failure. Here are some of the most common reasons why they give up the ghost:
- Heat: Chainsaws operate in demanding conditions, and the engine generates a lot of heat. Over time, this heat can degrade the insulation within the coil pack, leading to shorts and failures.
- Vibration: The constant vibration of a chainsaw can also take its toll on the coil pack. It can loosen connections, crack the housing, and damage internal components.
- Moisture: Moisture can seep into the coil pack, causing corrosion and short circuits. This is especially common if you store your chainsaw in a damp environment.
- Age: Like any electrical component, ignition coil packs have a limited lifespan. Over time, the insulation can break down, and the internal components can wear out.
- Air Gap: The air gap is the distance between the flywheel and the ignition coil. The specified air gap is around 0.010 inches. If the air gap is not maintained, the chainsaw might not work.
Personal Story: I once had a coil pack fail on me during a particularly humid summer. I had carelessly left my saw out in the shed, and the moisture had worked its way into the coil pack. The result? A chainsaw that refused to start, and a very frustrated lumberjack. Lesson learned: always store your chainsaw in a dry place!
Gathering Your Tools and Safety First
Before we even think about touching that multimeter, let’s make sure we have everything we need and that we’re working safely.
Essential Tools
- Multimeter: A digital multimeter is the key to testing your ignition coil pack. Make sure it’s set to measure resistance (ohms) and continuity.
- Screwdrivers: You’ll need a variety of screwdrivers (usually flathead and Phillips head) to remove the chainsaw’s housing and access the coil pack.
- Socket Set or Wrenches: Depending on your chainsaw model, you may need sockets or wrenches to remove the flywheel or other components.
- Feeler Gauges: To set the air gap between the ignition coil and the flywheel.
- Spark Plug Wrench: To remove the spark plug and inspect it.
- Work Gloves: Protect your hands from sharp edges and potential electrical shocks.
- Safety Glasses: Protect your eyes from debris.
- Chainsaw Manual: Your chainsaw’s manual is your best friend. It will provide specific instructions for your model.
Safety Precautions
- Disconnect the Spark Plug Wire: This is absolutely crucial! Disconnecting the spark plug wire prevents the engine from accidentally starting while you’re working on it.
- Let the Engine Cool Down: Never work on a hot engine. Allow it to cool down completely before you start disassembling anything.
- Work in a Well-Ventilated Area: Chainsaws can emit fumes, so make sure you’re working in a well-ventilated area.
- Read the Manual: Again, your chainsaw’s manual is your best friend. Read it carefully before you start working on it.
- When in doubt, consult a professional: If you’re not comfortable working on your chainsaw, take it to a qualified repair technician.
Step-by-Step Guide: Testing Your Ignition Coil Pack
Alright, let’s get down to business. Here’s a step-by-step guide to testing your chainsaw’s ignition coil pack with a multimeter.
Step 1: Accessing the Ignition Coil Pack
The first step is to gain access to the ignition coil pack. This usually involves removing the chainsaw’s housing. The exact procedure will vary depending on your chainsaw model, so consult your manual for specific instructions.
- Remove the Spark Plug Cover: This is usually a small plastic cover that protects the spark plug.
- Remove the Top Cover: This is the main housing that covers the engine. It’s usually held in place by screws or clips.
- Locate the Ignition Coil Pack: The ignition coil pack is usually located near the flywheel. It’s a small, rectangular component with wires leading to the spark plug and the magneto.
Example: On my Stihl MS 271, I need to remove the chain brake lever, the top cover, and the starter assembly to access the ignition coil pack. It’s a bit of a hassle, but it’s necessary to get to the heart of the problem.
Step 2: Visual Inspection
Before you start poking around with the multimeter, take a good look at the ignition coil pack. Look for any signs of damage, such as:
- Cracks: Cracks in the housing can allow moisture to enter and cause short circuits.
- Burn Marks: Burn marks indicate that the coil pack has overheated.
- Corrosion: Corrosion on the terminals or wires can impede the flow of electricity.
- Loose Connections: Loose connections can also cause problems.
If you see any of these signs, it’s likely that the coil pack is faulty and needs to be replaced.
Step 3: Testing the Primary Coil
The primary coil is the part of the ignition coil pack that receives the low-voltage current from the magneto. To test the primary coil, follow these steps:
- Set the Multimeter to Ohms (Ω): Select the lowest resistance range on your multimeter.
- Locate the Primary Terminals: These are usually the two terminals on the coil pack that connect to the magneto wires.
- Connect the Multimeter Probes: Connect one multimeter probe to each of the primary terminals.
- Read the Resistance: The multimeter will display a resistance reading. This reading should be within the range specified in your chainsaw’s manual. Typically, this range is very low, often less than 1 ohm.
Data Point: A healthy primary coil on a Stihl MS 271 should have a resistance of around 0.5 ohms. A reading outside of this range indicates a problem.
Insight: A very high resistance reading (or an open circuit) indicates that the primary coil is broken. A very low resistance reading (or a short circuit) indicates that the primary coil is shorted.
Step 4: Testing the Secondary Coil
The secondary coil is the part of the ignition coil pack that generates the high-voltage spark. To test the secondary coil, follow these steps:
- Set the Multimeter to Ohms (Ω): Select a higher resistance range on your multimeter (e.g., 20kΩ).
- Locate the Secondary Terminals: One terminal is the spark plug wire connector, and the other is usually grounded to the coil pack body.
- Connect the Multimeter Probes: Connect one multimeter probe to the spark plug wire connector and the other to the coil pack body (or the grounding terminal).
- Read the Resistance: The multimeter will display a resistance reading. This reading should be within the range specified in your chainsaw’s manual. Typically, this range is much higher than the primary coil, often between 2kΩ and 10kΩ.
Data Point: A healthy secondary coil on a Husqvarna 455 Rancher should have a resistance of around 4kΩ. A reading outside of this range indicates a problem.
Insight: Again, a very high resistance reading (or an open circuit) indicates that the secondary coil is broken. A very low resistance reading (or a short circuit) indicates that the secondary coil is shorted.
Step 5: Checking Continuity to Ground
This test checks for any unwanted short circuits to ground. To perform this test, follow these steps:
- Set the Multimeter to Continuity Mode: This mode is usually indicated by a diode symbol or a sound wave symbol.
- Connect the Multimeter Probes: Connect one multimeter probe to either of the primary terminals and the other to the coil pack body (or any metal part of the engine).
- Check for Continuity: The multimeter should not beep or indicate continuity. If it does, it means there’s a short circuit to ground, and the coil pack needs to be replaced.
Important Note: Some coil packs may have a slight continuity to ground. Consult your chainsaw’s manual for specific instructions.
Step 6: Setting the Air Gap
The air gap is the distance between the ignition coil pack and the flywheel. This gap is crucial for proper ignition. If the gap is too small, the coil pack can rub against the flywheel. If the gap is too large, the spark will be weak or non-existent.
- Loosen the Coil Pack Mounting Screws: Just enough so that you can move the coil pack slightly.
- Insert a Feeler Gauge: Use a feeler gauge of the correct thickness (usually 0.010 inches or 0.25 mm) between the coil pack and the flywheel magnets.
- Tighten the Mounting Screws: Tighten the mounting screws while holding the coil pack against the feeler gauge.
- Remove the Feeler Gauge: Once the screws are tightened, remove the feeler gauge.
Pro Tip: Some people use a business card as a makeshift feeler gauge. While this can work in a pinch, it’s always best to use a proper feeler gauge for accurate results.
Interpreting the Results and Making a Decision
Now that you’ve tested your ignition coil pack, it’s time to interpret the results and decide what to do next.
Scenario 1: All Tests Pass
If all the tests pass (the resistance readings are within the specified range, and there’s no continuity to ground), then your ignition coil pack is likely not the problem. You’ll need to look for other potential causes of your chainsaw’s problems, such as:
- Spark Plug: Check the spark plug for fouling, damage, or improper gap.
- Fuel System: Check the fuel lines, fuel filter, and carburetor for clogs or leaks.
- Compression: Check the engine’s compression. Low compression can prevent the engine from starting.
Scenario 2: One or More Tests Fail
If one or more of the tests fail (the resistance readings are outside the specified range, or there’s continuity to ground), then your ignition coil pack is likely faulty and needs to be replaced.
Cost-Benefit Analysis: Ignition coil packs are relatively inexpensive, so it’s usually worth replacing them if you suspect they’re faulty. A new coil pack can cost anywhere from \$20 to \$50, depending on the chainsaw model.
Replacing the Ignition Coil Pack
Replacing the ignition coil pack is usually a straightforward process. Simply remove the old coil pack and install the new one in its place. Make sure to set the air gap correctly.
Important Note: Always use a genuine or high-quality aftermarket replacement coil pack. Cheap, low-quality coil packs may not perform properly and can fail quickly.
Beyond the Multimeter: Other Diagnostic Tips
While a multimeter is a valuable tool for testing ignition coil packs, there are other diagnostic tips you can use to troubleshoot your chainsaw’s ignition system.
The Spark Test
This test checks whether the spark plug is producing a spark.
- Remove the Spark Plug: Remove the spark plug from the cylinder.
- Connect the Spark Plug to the Wire: Reconnect the spark plug to the spark plug wire.
- Ground the Spark Plug: Hold the spark plug against a metal part of the engine (e.g., the cylinder head).
- Pull the Starter Cord: Pull the starter cord and observe the spark plug.
If the spark plug is producing a strong, blue spark, then the ignition system is likely working properly. If the spark is weak, yellow, or non-existent, then there’s a problem with the ignition system.
Caution: Be careful not to touch the spark plug while pulling the starter cord. The spark can give you a nasty shock.
The Flywheel Key
The flywheel key is a small metal key that connects the flywheel to the crankshaft. If the flywheel key is sheared, the timing will be off, and the engine won’t start.
- Remove the Flywheel: Remove the flywheel from the crankshaft.
- Inspect the Flywheel Key: Inspect the flywheel key for damage.
If the flywheel key is sheared, it needs to be replaced.
Wood Species and Chainsaw Performance: A Tangential Tale
While we’re on the topic of chainsaws, I can’t resist sharing a bit of wisdom about wood species and how they affect chainsaw performance. I’ve spent years felling trees and processing firewood, and I’ve learned that not all wood is created equal.
- Hardwoods: Hardwoods like oak, maple, and hickory are dense and strong. They require a sharp chain and a powerful chainsaw to cut efficiently. They also tend to produce more heat and wear on the chain.
- Softwoods: Softwoods like pine, fir, and spruce are less dense and easier to cut. They require less power and produce less heat. However, they also tend to be more resinous, which can gum up the chain.
Data Point: Oak has a Janka hardness rating of around 1300 lbf, while pine has a Janka hardness rating of around 380 lbf. This means that oak is significantly harder than pine.
Personal Experience: I once spent an entire afternoon trying to fell a massive oak with a dull chain. It was a grueling experience, and I ended up wasting a lot of time and energy. Lesson learned: always keep your chain sharp, especially when cutting hardwoods.
Chainsaw Maintenance: Keeping Your Saw in Top Shape
Regular maintenance is essential for keeping your chainsaw in top shape and preventing problems like ignition coil pack failure. Here are some essential maintenance tasks:
- Sharpen the Chain: A sharp chain is essential for efficient and safe cutting. Sharpen the chain regularly using a file or a chain grinder.
- Clean the Air Filter: A dirty air filter can restrict airflow to the engine, causing it to overheat and run poorly. Clean the air filter regularly with soap and water.
- Check the Spark Plug: Check the spark plug for fouling, damage, or improper gap. Replace the spark plug as needed.
- Lubricate the Chain: Lubricate the chain with chain oil to reduce friction and wear.
- Clean the Saw: Clean the saw regularly to remove sawdust and debris.
- Store the Saw Properly: Store the saw in a dry place to prevent corrosion.
Final Thoughts: The Satisfaction of a Well-Maintained Chainsaw
There’s nothing quite like the satisfaction of a well-maintained chainsaw that starts easily and cuts through wood like butter. By understanding the basics of chainsaw ignition systems and performing regular maintenance, you can keep your saw running smoothly for years to come. And who knows, you might even save yourself a few trips to the repair shop.
So, the next time your chainsaw starts acting up, don’t panic. Grab your multimeter, follow these steps, and diagnose the problem yourself. You might be surprised at how easy it is to fix. And remember, a little knowledge and a little elbow grease can go a long way in the world of wood processing. Happy cutting!
