The sweet hum of a lawnmower engine on a sunny day is a beautiful sound. But when that hum turns into a sputtering cough, it can quickly turn your gardening plans upside down. One common culprit for a lawnmower refusing to start is a faulty ignition coil. This crucial component plays a vital role in converting low voltage from the battery into high voltage for the spark plugs, igniting the fuel-air mixture and bringing your mower to life.
This guide will walk you through the process of testing a lawnmower ignition coil using a multimeter. We’ll cover the basics of ignition coils, the different types of tests you can perform, and the steps involved in getting accurate readings. By the end of this article, you’ll be equipped to troubleshoot your lawnmower’s ignition system with confidence.
Understanding Ignition Coils
Before diving into the testing process, let’s briefly understand the role of an ignition coil in a lawnmower.
How an Ignition Coil Works:
- Battery Power: The battery provides low voltage (typically 12V) to the ignition coil.
- Primary Winding: This coil, with a large number of turns of wire, receives the low voltage from the battery.
- Magnetic Field: As electricity flows through the primary winding, it creates a magnetic field around it.
- Interrupting the Current: The ignition module or points (depending on the mower’s system) breaks the current flow to the primary winding. This sudden interruption collapses the magnetic field.
- High Voltage Induction: The collapsing magnetic field induces a very high voltage (thousands of volts) in the secondary winding of the coil.
- Spark Plug: The high voltage travels to the spark plug, creating a spark that ignites the fuel-air mixture in the cylinder.
Types of Ignition Coils:
- Conventional Coils: These are usually found in older lawnmowers with points-based ignition systems. They typically have two terminals: one for the primary winding and one for the secondary winding.
- Electronic Coils: Modern lawnmowers use electronic ignition systems with integrated coils. These coils are often more compact and may have multiple terminals depending on their specific design.
Testing with a Multimeter: Step-by-Step
Now let’s get down to business and see how to test a lawnmower ignition coil using a multimeter.
Essential Tools:
- Multimeter: A digital multimeter is recommended for accurate readings.
- Safety Glasses: Always protect your eyes while working on electrical systems.
- Gloves: Protective gloves will help prevent electrical shocks.
Steps:
1. Disconnect the Ignition Coil:
- Locate the ignition coil. It’s typically found near the spark plug(s) and may be attached to a metal bracket or the engine block.
- Disconnect the wire(s) leading to the coil. Use a wire brush or a small piece of sandpaper to clean any corrosion from the terminals.
2. Set the Multimeter for Resistance Measurement:
- Conventional Coil Test: Turn the dial of the multimeter to the ohms (Ω) setting.
- Electronic Coil Test: For some electronic coils, you might need to adjust the multimeter’s range depending on the specific coil and its specifications. Check the owner’s manual or online resources for guidance.
3. Testing the Primary Winding Resistance:
- Locate the Primary Terminals: Identify the terminals connected to the primary winding. This is usually the larger terminal or the terminal marked “BAT” or “+”.
- Connect the Meter Leads: Connect the positive (red) lead of the multimeter to one primary terminal and the negative (black) lead to the other primary terminal.
- Read the Resistance: Note the reading on the multimeter display. The primary winding resistance for a conventional coil is typically between 0.5 and 2 ohms. For electronic coils, the resistance value may vary.
4. Testing the Secondary Winding Resistance:
- Locate the Secondary Terminals: Locate the terminals connected to the secondary winding. The secondary terminal is typically smaller and marked “SP” or “-“.
- Connect the Meter Leads: Connect the positive (red) lead of the multimeter to the secondary terminal and the negative (black) lead to the primary terminal.
- Read the Resistance: Read the resistance on the multimeter display. The secondary winding resistance is typically in the range of 5,000 to 15,000 ohms for a conventional coil. Electronic coil resistance may differ.
5. Interpreting the Results:
- Primary Winding: If the primary winding resistance is much higher or lower than the expected range, it indicates a problem with the primary coil winding.
- Secondary Winding: A high or low secondary winding resistance also suggests an issue with the secondary winding. If the resistance is infinite (OL on the multimeter), it indicates a break in the winding.
- Resistance Fluctuation: If the resistance reading fluctuates while the probes are connected, it could indicate a faulty coil or an electrical connection problem.
6. Additional Tests (for Electronic Coils):
- Continuity Check: Check the continuity between the coil terminal and the spark plug wire. This ensures a good electrical connection.
- Diode Test: Some multimeters have a diode test function. If available, use this to check the diode within the electronic ignition coil.
Troubleshooting and Common Issues
If your ignition coil tests reveal any abnormalities, you might need to replace it. However, before doing so, it’s wise to check the following:
1. Spark Plug: A faulty spark plug can also cause starting issues. Inspect the spark plug for wear, cracks, or carbon buildup. Replace it if necessary.
2. Spark Plug Wire: Check the spark plug wire for damage or cracks. Ensure it’s securely connected to both the spark plug and the ignition coil.
3. Battery: A weak or dead battery can affect the ignition system. Test the battery voltage with a multimeter. If it’s low, replace or recharge the battery.
4. Ignition Switch: A faulty ignition switch can prevent the power supply to the ignition coil. Check the switch for proper operation.
5. Wiring Connections: Inspect all wiring connections related to the ignition system for corrosion, loose connections, or damage.
Conclusion:
Testing a lawnmower ignition coil with a multimeter can be a relatively straightforward process. By following the steps outlined in this article, you can determine if the coil is faulty and prevent further headaches with your lawnmower. Remember to exercise caution while working with electrical systems and always use safety gear to protect yourself.
If you’re unsure about any of the steps or if you encounter any unexpected results, it’s always best to consult a qualified mechanic for professional assistance.
With a little bit of knowledge and the right tools, you can troubleshoot your lawnmower’s ignition system and get back to enjoying a well-maintained and smoothly running lawn.
FAQ
What is an ignition coil, and what does it do?
An ignition coil is a crucial component in a lawn mower’s ignition system. It’s responsible for transforming the low-voltage electrical current from the battery into a high-voltage spark that ignites the fuel-air mixture in the engine’s combustion chamber. The coil works by converting the battery’s 12 volts into several thousand volts. This high voltage is then sent to the spark plug, creating the spark that ignites the fuel and allows the engine to run.
Why would I need to test a lawn mower ignition coil?
There are several reasons why you might need to test your lawn mower’s ignition coil. If your mower isn’t starting, sputtering, or running erratically, the coil might be the culprit. The coil’s primary function is to produce high-voltage electricity. If the coil isn’t working properly, it can cause the engine to misfire, run poorly, or fail to start at all.
What tools do I need to test a lawn mower ignition coil?
To test a lawn mower ignition coil, you’ll need a few basic tools, including a digital multimeter, a set of spark plug wires, and a pair of safety glasses. The multimeter is used to measure the resistance of the ignition coil’s primary and secondary windings. The spark plug wires are needed to connect the multimeter to the coil, and the safety glasses are for eye protection during the test.
How do I test a lawn mower ignition coil with a multimeter?
Testing a lawn mower ignition coil with a multimeter involves a series of simple steps. First, disconnect the ignition coil from the spark plug wire and the battery. Then, set your multimeter to the ohms setting and test the resistance of the coil’s primary and secondary windings. If the readings fall outside the manufacturer’s specifications, the coil is likely faulty and needs to be replaced.
What are the resistance readings I should expect?
The resistance readings you should expect when testing a lawn mower ignition coil will vary depending on the make and model of the mower. You can find the manufacturer’s specifications for the coil in your mower’s owner’s manual or online. A general rule of thumb is that the primary winding should have a resistance between 0.5 and 2 ohms, while the secondary winding should have a resistance between 8,000 and 12,000 ohms.
What if the ignition coil test shows a problem?
If your ignition coil test reveals that the coil is faulty, you’ll need to replace it. A bad coil can prevent the engine from starting or cause it to run poorly. To replace the coil, simply disconnect the old coil from the spark plug wire and the battery. Then, connect the new coil to the spark plug wire and battery. Ensure that the new coil is compatible with your lawn mower’s model.
What are some other troubleshooting tips for lawn mower problems?
While a faulty ignition coil is a common issue, there are other factors that could be contributing to your lawn mower’s problems. Start by inspecting the spark plug, making sure it’s clean and the gap is set correctly. Also, check the fuel system for any blockages or leaks. And, if your mower uses a carburetor, make sure it’s clean and adjusted properly.