How to Test Ignition Coils with a Multimeter (Chainsaw Repair Tips)
Hello everyone! Let’s dive into the world of chainsaw ignition coils. Modern chainsaws, with their sleek designs and powerful engines, often mask the complex electrical systems that bring them to life. A faulty ignition coil can turn your trusty saw into an expensive paperweight. That’s where understanding how to test an ignition coil with a multimeter becomes essential. I’ve spent years felling trees, bucking logs, and splitting firewood, and I can tell you firsthand that a dead chainsaw in the middle of a job is incredibly frustrating. Knowing how to diagnose and potentially fix the problem yourself can save you time, money, and a lot of headaches. So, let’s get started with this chainsaw repair tips.
Understanding the Ignition Coil: The Heart of Your Chainsaw
Before we grab our multimeters, let’s understand what an ignition coil does and why it’s so crucial. In simple terms, the ignition coil is like a mini-transformer. It takes the low voltage from the chainsaw’s magneto and converts it into a high-voltage spark that ignites the fuel-air mixture in the cylinder. Without a functioning ignition coil, there’s no spark, no combustion, and no roaring chainsaw.
Think of it this way: your chainsaw engine needs a tiny lightning bolt to get going. The ignition coil is what generates that lightning bolt.
Key Components of an Ignition System
To properly diagnose ignition issues, it’s important to know the components involved.
- Magneto: The magneto generates the initial low-voltage electrical current. It’s typically located near the flywheel.
- Ignition Coil: As discussed, this transforms the low voltage into high voltage.
- Spark Plug: The spark plug receives the high-voltage current from the ignition coil and creates the spark within the cylinder.
- Flywheel: The flywheel contains magnets that interact with the magneto to produce electricity.
- Kill Switch: This switch grounds the ignition system, stopping the spark and shutting off the engine.
Why Test the Ignition Coil?
Over time, ignition coils can fail due to heat, vibration, or simply age. Common symptoms of a failing ignition coil include:
- Difficulty starting: The engine might crank but not start, or it might start intermittently.
- Weak spark: The spark may be too weak to ignite the fuel-air mixture effectively.
- Engine misfires: The engine might run roughly or stall frequently.
- No spark at all: The engine won’t start and there’s no spark at the spark plug.
Testing the ignition coil with a multimeter allows you to determine if the coil is functioning within its specified parameters, or if it’s the source of your chainsaw’s problems. It’s a relatively simple process that can save you the cost of replacing other parts unnecessarily.
Safety First: Disconnecting and Grounding
Before we begin any electrical testing, safety is paramount. Here’s what you need to do:
- Disconnect the Spark Plug Wire: Remove the spark plug wire from the spark plug. This prevents accidental starting. Secure the wire away from the spark plug.
- Ground the Spark Plug Wire: Attach the spark plug wire to the engine block or chassis. This provides a safe path for any residual electricity to discharge. You can use a test lead with alligator clips for this.
- Allow the Engine to Cool: If the engine has been running, allow it to cool completely before working on it.
- Wear Safety Glasses: Protect your eyes from any debris.
- Work in a Well-Ventilated Area: Avoid working in enclosed spaces where fuel fumes can accumulate.
Tools You’ll Need
- Multimeter: A digital multimeter (DMM) is essential for measuring resistance and voltage. Make sure it’s in good working order and the battery is charged.
- Screwdrivers: You’ll need screwdrivers to access the ignition coil and disconnect any wires.
- Pliers: Pliers can be helpful for gripping and manipulating wires.
- Spark Plug Wrench: To remove and inspect the spark plug.
- Service Manual (Optional): A service manual for your specific chainsaw model can provide valuable information about the ignition coil’s specifications and testing procedures.
Step-by-Step Guide to Testing Your Ignition Coil
Here’s a detailed, step-by-step guide on how to test your chainsaw’s ignition coil with a multimeter. I’ll break down each step and explain the concepts involved.
Step 1: Visual Inspection
Before diving into electrical testing, give the ignition coil a thorough visual inspection. Look for any signs of damage, such as:
- Cracks: Cracks in the coil housing can allow moisture and contaminants to enter, causing short circuits and failure.
- Burn Marks: Burn marks indicate overheating, which can damage the coil’s internal components.
- Corrosion: Corrosion on the terminals can impede electrical flow.
- Loose Wires: Check for any loose or disconnected wires.
If you find any of these issues, the ignition coil is likely faulty and needs to be replaced.
My Experience: I once had a chainsaw that kept cutting out. After a visual inspection, I found a tiny crack in the ignition coil housing. Even though it was small, it was enough to let moisture in and cause intermittent failures. Replacing the coil solved the problem.
Step 2: Setting Up Your Multimeter
Now, let’s get your multimeter ready.
- Turn on the Multimeter: Turn on your multimeter and set it to the “Ohms” (Ω) setting. This setting measures resistance. You’ll likely have different ranges to choose from (e.g., 200Ω, 2kΩ, 20kΩ). Start with the lowest range and increase it if necessary.
- Connect the Test Leads: Insert the black test lead into the “COM” (common) jack and the red test lead into the “Ω” (ohms) jack.
Step 3: Testing the Primary Resistance
The primary resistance is the resistance of the primary winding of the ignition coil. This winding receives the low-voltage current from the magneto.
- Locate the Primary Terminals: Identify the primary terminals on the ignition coil. These are typically the two smaller terminals. Refer to your chainsaw’s service manual if you’re unsure.
- Connect the Test Leads: Touch the red test lead to one primary terminal and the black test lead to the other primary terminal.
- Read the Resistance Value: Observe the resistance reading on the multimeter. The expected resistance value will vary depending on the chainsaw model, but it’s typically between 0.5 and 5 ohms. Refer to your service manual for the specific value for your chainsaw.
Interpreting the Results:
- Within Range: If the resistance reading is within the specified range, the primary winding is likely good.
- Zero Resistance (Short Circuit): If the resistance reading is zero ohms, there’s a short circuit in the primary winding. The coil is faulty and needs to be replaced.
- Infinite Resistance (Open Circuit): If the resistance reading is infinite (OL or 1 on the multimeter display), there’s an open circuit in the primary winding. The coil is faulty and needs to be replaced.
- Significantly Higher or Lower Resistance: If the resistance reading is significantly higher or lower than the specified range, the primary winding is likely damaged and the coil should be replaced.
Example: Let’s say your service manual specifies a primary resistance of 2 ohms. If your multimeter reads 1.8 ohms, that’s within the acceptable range. But if it reads 0 ohms or infinite resistance, the coil is definitely bad.
Step 4: Testing the Secondary Resistance
The secondary resistance is the resistance of the secondary winding of the ignition coil. This winding produces the high-voltage current that goes to the spark plug.
- Locate the Secondary Terminals: Identify the secondary terminals on the ignition coil. One terminal is typically the spark plug wire connection, and the other is a ground connection.
- Connect the Test Leads: Touch the red test lead to the spark plug wire connection and the black test lead to the ground connection.
- Read the Resistance Value: Observe the resistance reading on the multimeter. The expected secondary resistance value is typically much higher than the primary resistance, ranging from 2,000 to 15,000 ohms (2kΩ to 15kΩ). Again, refer to your service manual for the specific value for your chainsaw.
Interpreting the Results:
- Within Range: If the resistance reading is within the specified range, the secondary winding is likely good.
- Zero Resistance (Short Circuit): If the resistance reading is zero ohms, there’s a short circuit in the secondary winding. The coil is faulty and needs to be replaced.
- Infinite Resistance (Open Circuit): If the resistance reading is infinite (OL or 1 on the multimeter display), there’s an open circuit in the secondary winding. The coil is faulty and needs to be replaced.
- Significantly Higher or Lower Resistance: If the resistance reading is significantly higher or lower than the specified range, the secondary winding is likely damaged and the coil should be replaced.
My Insight: I once encountered a chainsaw with a weak spark. The primary resistance was fine, but the secondary resistance was significantly lower than the specified range. This indicated a partial short circuit in the secondary winding, which was weakening the spark. Replacing the coil restored the engine’s power.
Step 5: Testing the Spark Plug Wire (If Detachable)
If your chainsaw has a detachable spark plug wire, you can test its resistance separately.
- Disconnect the Spark Plug Wire: Disconnect the spark plug wire from both the ignition coil and the spark plug.
- Connect the Test Leads: Touch the red test lead to one end of the wire and the black test lead to the other end.
- Read the Resistance Value: The resistance of the spark plug wire should be relatively low, typically a few thousand ohms (a few kΩ). Refer to your service manual for the specific value.
Interpreting the Results:
- Within Range: If the resistance reading is within the specified range, the spark plug wire is likely good.
- Zero Resistance (Short Circuit): If the resistance reading is zero ohms, there’s a short circuit in the spark plug wire. The wire should be replaced.
- Infinite Resistance (Open Circuit): If the resistance reading is infinite (OL or 1 on the multimeter display), there’s an open circuit in the spark plug wire. The wire should be replaced.
- Significantly Higher Resistance: If the resistance reading is significantly higher than the specified range, the spark plug wire is likely damaged and should be replaced.
Important Note: Some spark plug wires have a built-in resistor. This will increase the resistance reading. Consult your service manual for the correct value.
Step 6: Checking for Continuity to Ground (Optional)
This test checks for any unwanted electrical connection between the ignition coil windings and the engine ground.
- Set the Multimeter: Set your multimeter to the “Continuity” setting (often indicated by a diode symbol or a sound wave symbol).
- Connect the Test Leads: Touch the red test lead to one of the ignition coil terminals (either primary or secondary) and the black test lead to the engine block or chassis.
- Observe the Reading: If the multimeter beeps or shows a reading close to zero ohms, there’s continuity to ground, indicating a short circuit. The ignition coil is faulty and needs to be replaced. If the multimeter shows no continuity (OL or 1 on the display), there’s no unwanted connection to ground.
Why This Matters: A short circuit to ground can drain the spark energy and prevent the engine from starting.
Interpreting Your Results: A Summary
Here’s a quick summary of how to interpret your multimeter readings:
- Primary Resistance:
- Within Range: Good
- Zero Ohms: Short Circuit – Replace Coil
- Infinite Ohms: Open Circuit – Replace Coil
- Significantly Out of Range: Damaged – Replace Coil
- Secondary Resistance:
- Within Range: Good
- Zero Ohms: Short Circuit – Replace Coil
- Infinite Ohms: Open Circuit – Replace Coil
- Significantly Out of Range: Damaged – Replace Coil
- Spark Plug Wire Resistance:
- Within Range: Good
- Zero Ohms: Short Circuit – Replace Wire
- Infinite Ohms: Open Circuit – Replace Wire
- Significantly Higher Resistance: Damaged – Replace Wire
- Continuity to Ground:
- Continuity (Beep or Near Zero Ohms): Short Circuit – Replace Coil
- No Continuity (OL or 1): Good
What If the Ignition Coil is Bad?
If your testing reveals that the ignition coil is faulty, the only real solution is to replace it. Fortunately, ignition coils are relatively inexpensive and easy to replace.
- Purchase a Replacement Coil: Buy a new ignition coil that’s specifically designed for your chainsaw model. You can find these at most chainsaw repair shops or online retailers.
- Disconnect the Old Coil: Disconnect the wires from the old ignition coil. Take note of the wire connections so you can reconnect them correctly to the new coil.
- Remove the Old Coil: Remove the screws or bolts that hold the old ignition coil in place.
- Install the New Coil: Install the new ignition coil in the same position as the old one. Tighten the screws or bolts securely.
- Reconnect the Wires: Reconnect the wires to the new ignition coil, making sure they’re connected to the correct terminals.
- Reconnect the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
- Test the Chainsaw: Start the chainsaw and see if it runs properly.
Other Potential Causes of Ignition Problems
Even if your ignition coil tests good, your chainsaw might still have ignition problems. Here are some other potential causes to consider:
- Faulty Spark Plug: A cracked, fouled, or worn spark plug can prevent the engine from starting. Inspect the spark plug and replace it if necessary. The spark plug gap should also be checked and adjusted according to the manufacturer’s specifications.
- Dirty Air Filter: A clogged air filter can restrict airflow and prevent the engine from starting. Clean or replace the air filter.
- Contaminated Fuel: Old or contaminated fuel can cause starting problems. Drain the fuel tank and replace it with fresh fuel.
- Clogged Fuel Filter: A clogged fuel filter can restrict fuel flow to the carburetor. Replace the fuel filter.
- Carburetor Issues: A dirty or improperly adjusted carburetor can cause starting problems. Clean or rebuild the carburetor.
- Faulty Kill Switch: A faulty kill switch can ground the ignition system and prevent the engine from starting. Disconnect the kill switch and see if the engine starts.
- Weak Magneto: A weak magneto can produce insufficient voltage to power the ignition coil. Test the magneto’s output voltage with a multimeter.
- Incorrect Air Gap: The air gap between the flywheel and the ignition coil must be correct for the ignition system to function properly. Refer to your service manual for the correct air gap specification and adjust it if necessary. Typically, this is around 0.010″ to 0.020″ (0.25mm to 0.50mm).
- Loose Connections: Check all electrical connections in the ignition system for looseness or corrosion. Clean and tighten any loose connections.
Real-World Case Study: The Stubborn Stihl
I once spent an entire afternoon troubleshooting a Stihl MS 290 that refused to start. I tested the ignition coil, and it seemed fine. I replaced the spark plug, cleaned the air filter, and even rebuilt the carburetor, but nothing worked. Finally, I decided to check the air gap between the flywheel and the ignition coil. It was way too wide! I adjusted the air gap to the correct specification, and the chainsaw fired up immediately. This taught me that even if the major components are working correctly, something as simple as an incorrect air gap can cause major problems.
Chain Saw Maintenance Tips
While you’re working on your chainsaw, it’s a good idea to perform some routine maintenance. Here are a few tips:
- Sharpen the Chain: A sharp chain is essential for efficient cutting and safety. Sharpen the chain regularly using a file or a chain grinder.
- Lubricate the Chain: Use bar and chain oil to keep the chain lubricated. This reduces friction and wear.
- Clean the Air Filter: Clean the air filter regularly to maintain proper airflow.
- Inspect the Spark Plug: Inspect the spark plug regularly and replace it if necessary.
- Check the Fuel Lines: Check the fuel lines for cracks or leaks. Replace them if necessary.
- Tighten the Nuts and Bolts: Check all nuts and bolts for tightness. Tighten them if necessary.
- Store the Chainsaw Properly: Store the chainsaw in a dry place. Drain the fuel tank before storing it for extended periods.
Wood Processing and Firewood Preparation: Strategic Insights
Beyond chainsaw maintenance, let’s consider some strategic insights related to wood processing and firewood preparation.
- Wood Selection: Choosing the right wood is crucial for efficient burning and heat output. Hardwoods like oak, maple, and beech are denser and burn longer than softwoods like pine and fir. Aim for a moisture content of 20% or less for optimal burning.
- Felling Techniques: Safe and efficient felling techniques are essential for logging. Use proper wedges and directional felling cuts to control the direction of the fall.
- Bucking and Splitting: Bucking logs into manageable lengths and splitting them into firewood requires the right tools and techniques. A hydraulic log splitter can significantly increase efficiency and reduce physical strain. I personally use a 27-ton hydraulic splitter, which allows me to split even the toughest oak logs with ease.
- Drying and Seasoning: Properly drying and seasoning firewood is essential for reducing moisture content and improving burning efficiency. Stack the firewood in a well-ventilated area and allow it to dry for at least six months, preferably a year.
- Stacking Methods: Efficient stacking methods can maximize drying and storage space. Consider using a traditional woodpile or a more modern storage rack.
- Safety Gear: Always wear appropriate safety gear when operating a chainsaw or log splitter, including safety glasses, hearing protection, gloves, and sturdy boots.
Final Thoughts
Testing your chainsaw’s ignition coil with a multimeter is a valuable skill for any woodworker or chainsaw user. It can save you time, money, and frustration by allowing you to diagnose and potentially fix ignition problems yourself. Remember to always prioritize safety and consult your service manual for specific instructions and specifications for your chainsaw model. And don’t forget the importance of regular maintenance to keep your chainsaw running smoothly for years to come.
By combining this knowledge with proper wood selection, efficient processing techniques, and a commitment to safety, you can enjoy the benefits of a well-maintained chainsaw and a plentiful supply of firewood. Now, go out there and get those logs bucked and split!
