How to Test a Motorcycle Ignition Coil: 12 Steps (& Symptoms)
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A motorcycle ignition coil is a vital ignition system component that converts the low-voltage electrical current from the battery into a high-voltage spark. It then delivers this spark to the spark plugs, igniting the air-fuel mixture in the engine cylinders and enabling combustion and power generation.
But what do you do if it suddenly becomes compromised? And how exactly does one go about testing a motorcycle ignition coil?
Testing a motorcycle ignition coil entails checking primary and secondary resistance, testing for open or short circuits, verifying spark strength, and visually inspecting the ignition coil and spark plug wires. Some tests require a spark plug wire tester, while the rest employ a digital multimeter.
Since the motorcycle ignition coil is part of the ignition system, I recommend following the guidelines in my article on How to Test a Motorcycle Rectifier first. Once you complete those preliminary checks, proceed with the below steps on how to test a motorcycle ignition coil:
- Safety First
- Locate the Ignition Coil
- Inspect the Ignition Coil
- Disconnect the Spark Plug Wires
- Measure and Read Primary Resistance
- Take Secondary Resistance Readings
- Test for Open and Short Circuits
- Visually Inspect the Spark Plug Wires
- Reconnect the Spark Plug Wires
- Test the Ignition System
- Verify Spark at the Spark Plugs
- Seek Professional Assistance
By scrutinizing the battery and conducting related tests first, you ensure that your electrical system is in good condition and can provide sufficient power to the coil. Moreover, ascertaining these facets makes for a systematic and thorough approach to diagnosing your motorcycle ignition coil — helping eliminate potential issues from the battery, voltage regulator, or other electrical components.
How to Test a Coil on a Motorcycle
Before testing your motorcycle ignition coil, ensure that your battery is fully charged (not overcharged) and not suffering from parasitic draw. After which, you need to perform the following tests on your two-wheeler:
- Open-circuit voltage test
- DC voltage regulator test
- Voltage drop test
- Regulator bypass
- Diode leak test
- Motorcycle rectifier test
Doing these initial tests helps rule out other possible culprits behind your ignition system hiccups. However, if all these other elements check out, the next step is to scrutinize your motorcycle ignition coil directly by following the below procedures:
1. Safety First.
Before troubleshooting steps on the motorcycle ignition coil, ensure that your thumper is parked on a stable, level surface and that the ignition is turned off. Additionally, wear protective equipment like gloves and goggles to prevent accidents or injuries.
2. Locate the Ignition Coil.
Once you have secured yourself and your two-wheeler, locate the ignition coil on your bike. Depending on the year, make, and model that you have, you would typically find the motorcycle coil in one of these three places:
Near the Engine
The ignition coil is often positioned near the power mill, usually mounted on the frame or engine block. Depending on the motorcycle’s design, it may be placed on either side of the engine or at the front or rear.
(TIP: If you are a beginner or new to your bike’s electrical systems, you can easily spot the motorcycle ignition coil by looking for a cylindrical or rectangular-shaped component with two or more spark plug wires connected to it.)
Under the Fuel Tank
In some motorcycles with fuel tanks positioned over the engine, the ignition coil can be found beneath the fuel tank. However, accessing a motorcycle ignition coil with this setup may require removing the fuel tank entirely.
Near the Battery or Electrical System
In certain models, the motorcycle ignition coil is near the battery or other electrical components. Modern sports bikes, cruisers, tourers, and ADV/dual-sport motorcycles typically have this arrangement, as the latter allows for shorter wiring connections and more efficient power transfer.
3. Inspect the Ignition Coil.
Inspect the ignition coil for signs of physical damage, such as corrosion or cracks. If none are found, gently wiggle the ignition coil and its connectors to check for any signs of looseness or poor connections.
Furthermore, consider the condition of the coil housing, terminals, and wiring. Remember that any visible damage or abnormality found could indicate a faulty ignition coil and may warrant repair or replacement.
While at it, check for proper mounting. This entails verifying that the motorcycle ignition coil is securely mounted in its designated location and checking for loose or missing mounting bolts or brackets. Any attachment aids found loose, deteriorated, or displaced should immediately be replaced to ensure the ignition coil remains stable during operation.
4. Disconnect the Spark Plug Wires.
At this point, motorheads typically have already ruled out issues with the mounting and condition of the motorcycle ignition coil. If this is the case, examine your thumper’s spark ignition.
To proceed, remove the spark plug wires from the ignition coil by gently pulling them away. Also, take note of the correct placement of the detached plug wires by labeling each wire to ensure proper reconnection later.
5. Measure and Read Primary Resistance.
Primary resistance refers to the electrical resistance in the primary winding of a motorcycle ignition coil. It is measured between the positive and negative terminals of the ignition coil and is lower in value than secondary resistance (usually ranging from 0.5—5 Ohms, depending on OEM specs).
This measurement is crucial since it helps determine the proper functionality of the primary winding and potential issues with the ignition coil’s internal wiring or connections.
To measure primary resistance, use a digital multimeter and set it to the Ohms mode. Connect the multimeter’s positive (red) lead to the ignition coil’s positive terminal and the negative (black) lead to the coil’s negative terminal.
With this process, you would want to get a reading within the specified range for your motorcycle. Anything outside the normal range (either low or excessive) would indicate discontinuity or a short circuit in the primary winding.
6. Take Secondary Resistance Readings.
Secondary resistance, on the other hand, refers to the electrical resistance in the secondary winding of the ignition coil. It is measured between the positive terminal and the high-voltage output terminal connecting to the spark plug wire. Compared to primary resistance, it is usually higher in value (typically ranging from 5,000—15,000 Ohms or more, depending on OEM specs).
This measurement helps determine the ignition coil’s ability to generate a strong spark at the spark plug. Taking readings is still a must, even if primary resistance values fall within range.
Measuring secondary resistance merits the same tool and settings. The only difference is that you need to connect the multimeter’s positive lead to the ignition coil’s positive terminal and the negative lead to the spark plug wire socket.
Getting out-of-range values mostly signify the same complications a low or excessive primary resistance would have — but with accompanying symptoms like an intermittent spark, misfiring, and poor engine performance.
7. Test for Open and Short Circuits.
Depending on the results of your primary and secondary resistance readings, test for current overloading or discontinuity in the ignition coil. If you get low resistance readings, a short circuit test is required. Conversely, excessive resistance readings warrant an open circuit test.
Using the continuity or diode mode on a digital multimeter like Klein Tools MM450 Multimeter (view on Amazon), check for any short circuits within the ignition coil. Connect the leads to the terminals. The outcome you would want is the absence of a beeping sound — an indication that no short circuit is present.
With the same settings on the multimeter, touch the positive lead to the coil’s positive terminal and the negative lead to the spark plug wire socket. This time around, test for open circuit. The goal here is inverse — there should be continuity or a beeping sound to indicate a complete circuit.
8. Visually Inspect the Spark Plug Wires.
Although seldom, there are instances where there are no issues with the ignition coil or its housing, terminals, wiring, and connections after performing the first seven steps in this guide. And if you experience something similar, it is time to check on electrical components like the spark plug wires.
If current flow and continuity are normal, chances are the spark plug wires are damaged, frayed, or severely worn. If so, replace any damaged wires as needed.
9. Reconnect the Spark Plug Wires.
Once you have completed the testing and inspection of the motorcycle ignition coil and other relevant electrical components and have made necessary repairs or replacements, reattach the spark plug wires to their respective terminals on the coil.
Follow the markings you made in step #4, and ensure the spark plug wires are firmly seated and properly connected.
10. Test the Ignition System.
With the motorcycle ignition coil reconnected, start your thumper and observe the engine’s behavior. The ignition coil is functioning correctly if the power mill runs smoothly without any misfires or hesitation. Otherwise, further troubleshooting may be required.
11. Verify Spark at the Spark Plugs.
Even if the motorcycle ignition system works uninterrupted at this point, I strongly recommend confirming spark output at the spark plugs for added measure. This way, you can ascertain that your ignition system’s internal wiring and external electrical components are in good shape and problem-free.
To confirm that the motorcycle ignition coil produces sparks, remove a spark plug from the engine and connect the spark plug wire to it. Next, ground the spark plug against the engine block using insulated pliers and crank the engine.
The aim is to get a prominent spark at the spark plug’s electrode. Anything short of this outcome may signify the need to replace your spark plugs.
12. Seek Professional Assistance.
If all else fails after following all the steps in this guide, seek the expertise of a professional mechanic or technician. They will have specialized equipment and knowledge to diagnose and resolve complex ignition system issues that may be too intricate or deeply rooted to be addressed by these general guidelines.
Tools for testing:
- Diagnostic scan tool like Autel MaxiCOM MK808S Bi-Directional Scan Tool (view on Amazon)
- Voltmeter
- Digital Multimeter
- Measurement probes
- Ohm meter
- Spark plug wire tester like GTC505 Engine Ignition Analyzer (view on Amazon)
- Spark plug socket
- Insulated pliers
- Test light
- Battery charger or maintainer
Symptoms of a Weak Ignition Coil
Engine Misfiring
When an ignition coil is weak, it may lead to misfires, which result in irregular or uneven engine operation. These misfires occur when the weak ignition coil fails to provide a strong enough spark to ignite the fuel-air mixture consistently, disrupting the combustion process and causing the engine to perform poorly.
Performance Issues
In addition to engine misfiring, a flawed motorcycle ignition coil may also result in the engine not running smoothly and exhibiting symptoms such as power loss, hesitation, or stumbling during acceleration.
These performance hiccups are attributed to the ignition coil failing to create a strong spark, causing the power mill to run rough at idle, shudder, exhibit uneven idle speed, stall or shut off abruptly, or give off a choppy engine sound.
In contrast to its inability to ignite the air-fuel mixture, the motorcycle ignition coil may ignite the engine’s cylinders prematurely, contributing to backfiring or loud, popping bangs from the exhaust. A weak ignition coil typically results in reduced engine power and overall performance. When this happens, your motorcycle may feel sluggish, lack responsiveness, or struggle to maintain higher speeds.
Starting Difficulties
Starting issues are not typically an initial sign of a compromised motorcycle ignition coil. But these symptoms manifest when the spark plug is impacted (if not the culprit behind the problem).
An ignition coil gone bad typically goes hand in hand with a defective plug or spark plug wires. As such, efficiency in starting your motorcycle is bound to be adversely affected, as the inadequate spark will struggle to ignite your two-wheeler’s air-fuel mixture.
Reduced Fuel Efficiency
Because of potential challenges with igniting the air-fuel mixture, it would be unsurprising for a defective motorcycle ignition coil to translate to incomplete combustion and inefficient fuel consumption. Consequently, you may notice decreased fuel efficiency and increased fuel consumption from your two-wheeler until you can address its ignition-related concerns.
Illuminated Check Engine Light
In some cases, a weak motorcycle ignition coil can trigger the CEL to illuminate on the instrument cluster. This happens when the Engine Control Unit or ECU detects ignition-related issues.
Depending on the ignition coil problem’s severity, fault codes may or may not accompany this warning light. Having a high-spec diagnostic scan tool handy is highly advised but optional.
Cost of an Ignition Coil Repair
The cost of repairing a motorcycle ignition coil is contingent on several factors, including the make and model of the motorcycle, the specific issue with the ignition coil, and the labor rates in your area. On average, repairing a motorcycle ignition coil can range from $50 to $300 (if not more for replacement).
Remember that this estimate is a general range, and the actual cost may differ depending on the factors mentioned. It is always recommended to consult a qualified mechanic or technician who can diagnose the exact issue with the ignition coil and provide an accurate cost estimate for the repair.
Can a Motorcycle Run With a Busted Ignition Coil?
No, a motorcycle typically cannot run with a completely busted ignition coil. The ignition coil generates the high-voltage spark needed to ignite the engine cylinders’ air-fuel mixture.
If the ignition coil becomes completely non-functional or severely damaged, it will not be capable of producing the necessary spark. Hence, the engine will not start or run.
Conclusion — How to Test a Motorcycle Ignition Coil
To summarize, here are the general guidelines on how to test a motorcycle coil:
- Safety First
- Locate the Ignition Coil
- Inspect the Ignition Coil
- Disconnect the Spark Plug Wires
- Measure and Read Primary Resistance
- Take Secondary Resistance Readings
- Test for Open and Short Circuits
- Visually Inspect the Spark Plug Wires
- Reconnect the Spark Plug Wires
- Test the Ignition System
- Verify Spark at the Spark Plugs
- Seek Professional Assistance
By following this sequence, you can effectively test a motorcycle ignition coil and determine its functionality. However, remember that these troubleshooting procedures may vary based on service manual recommendations and your motorcycle’s specific make and model.
