Ensuring the optimal performance of your vehicle’s ignition system is crucial for reliable engine operation. Among the key components within this system are ignition coils, which play a vital role in generating the high voltage required for spark plug ignition. To maintain the efficiency of your ignition coils, periodic testing is essential. This article will guide you through the process of using a multimeter to test ignition coils, ensuring that they are functioning optimally for a smooth-running engine.
Before embarking on the testing procedure, it is imperative to gather the necessary tools and observe appropriate safety precautions. A digital multimeter is essential for accurate measurements, and it should be set to the appropriate voltage and resistance scales. Additionally, ensure that the vehicle is parked on a level surface with the engine turned off and the ignition key removed. Wear appropriate safety gear, including gloves and eye protection, throughout the testing process.
With the multimeter prepared and safety precautions in place, you can begin the testing procedure. Firstly, identify the ignition coils in your vehicle’s engine compartment. They are typically located near the spark plugs and are connected by high-voltage wires. Once identified, disconnect the negative terminal of the battery to prevent electrical shock during testing. Next, remove the spark plug wires from the ignition coils. Use the multimeter to measure the primary resistance of each coil by connecting the leads to the positive and negative terminals of the coil. The resistance should be within the range specified by the manufacturer, typically between 0.5 and 2 ohms.
Multimeter Fundamentals
A multimeter is a versatile electrical testing device used to measure various electrical properties such as voltage, current, and resistance. It operates based on the principle of Ohm’s Law, which states that the voltage across a conductor is directly proportional to the current flowing through it and the resistance of the conductor. Multimeters have multiple modes, including:
Voltage Measurement
The voltage mode measures the potential difference between two points in a circuit. The multimeter is connected in parallel with the circuit, and the display shows the voltage reading in volts. To ensure accurate voltage measurement, the multimeter should have a high input impedance to minimize loading effects on the circuit.
Current Measurement
The current mode measures the flow of electrons through a circuit. The multimeter is connected in series with the circuit, and the display shows the current reading in amperes. To prevent damaging the multimeter, ensure it can handle the expected current flow. Different types of current measurement include AC (alternating current) and DC (direct current).
Resistance Measurement
The resistance mode measures the opposition to current flow in a circuit. The multimeter is connected in parallel with the component being tested, and the display shows the resistance reading in ohms. Resistance measurement is used to test continuity (presence of an electrical path), identify faulty components, and determine the value of resistors.
| Measurement Type | Connection | Units |
|---|---|---|
| Voltage | Parallel | Volts (V) |
| Current | Series | Amperes (A) |
| Resistance | Parallel | Ohms (Ω) |
Identifying the Ignition Coils
First, we need to locate the ignition coils in our vehicle. They’re usually mounted on the engine or near it, and they’ll have wires connected to them that lead to the spark plugs. Ignition coils can come in different shapes and sizes, so it’s best to consult your car’s manual or online resources to identify them accurately.
Checking the Primary Resistance
To test the primary resistance of an ignition coil, we’ll need to set our multimeter to the ohms (Ω) setting. Next, we’ll need to locate the two terminals on the ignition coil that are connected to the primary circuit. These terminals are usually labeled with a “+” and a “-“. Once we’ve found the terminals, we’ll need to touch the multimeter probes to them and read the resistance value. The resistance value should be within the range specified in our vehicle’s manual. If it’s not, the ignition coil may be faulty and need to be replaced.
Checking the Secondary Resistance
To test the secondary resistance of an ignition coil, we’ll need to set our multimeter to the kilohms (kΩ) setting. Next, we’ll need to locate the two terminals on the ignition coil that are connected to the secondary circuit. These terminals are usually labeled with a “+” and a “-“. Once we’ve found the terminals, we’ll need to touch the multimeter probes to them and read the resistance value. The resistance value should be within the range specified in our vehicle’s manual. If it’s not, the ignition coil may be faulty and need to be replaced.
Testing Primary Resistance
The primary resistance test measures the resistance between the positive and negative terminals of the ignition coil. This test can help identify if the coil is open or has a high resistance that can prevent it from functioning properly. Open a digital multimeter and set it to the ohms (Ω) setting. Then, follow these steps:
1. Locate the ignition coil.
The ignition coil is usually located near the distributor or on the engine block.
2. Disconnect the ignition coil wires.
There are two wires that connect to the ignition coil: a primary wire and a secondary wire. Disconnect both of these wires.
3. Connect the multimeter leads to the ignition coil terminals.
Connect one lead to the positive terminal and the other lead to the negative terminal. The multimeter should display a reading in ohms.
| Ignition Coil Type | Primary Resistance (Ω) |
|---|---|
| Standard Ignition Coil | 0.4 – 2.0 |
| High-Performance Ignition Coil | 0.1 – 0.5 |
4. Compare the reading to the specification.
The specification for the ignition coil’s primary resistance can be found in the vehicle’s repair manual. If the reading is outside of the specification, the ignition coil may need to be replaced.
Measuring Secondary Resistance
Secondary resistance is the resistance between the two high-voltage terminals of the coil. This test helps determine if the coil’s windings are open or shorted. To measure secondary resistance:
- Set the multimeter to the ohms (Ω) setting.
- Connect one multimeter lead to each high-voltage terminal of the coil.
- Read the multimeter display. The resistance should be within the manufacturer’s specifications, typically around 5 to 15 kΩ.
- If the resistance is too high, the windings may be open or damaged. If the resistance is too low, the windings may be shorted.
Here’s a table summarizing the test results:
| Resistance | Meaning |
|---|---|
| Within manufacturer’s specifications | Coil is functioning properly |
| Too high | Windings may be open or damaged |
| Too low | Windings may be shorted |
Note that the secondary resistance may vary slightly depending on the type of coil and its temperature. Always refer to the manufacturer’s specifications for the correct values.
Verifying Voltage Output
A multimeter can be used to measure the voltage output of an ignition coil. To do this, connect the positive lead of the multimeter to the positive terminal of the ignition coil and the negative lead of the multimeter to the negative terminal of the ignition coil. Then, set the multimeter to the volts AC setting and crank the engine. The multimeter should read the voltage output of the ignition coil.
A typical ignition coil will produce an output voltage of between 10,000 and 20,000 volts. If the output voltage is below this range, the ignition coil may be faulty and need to be replaced.
Measuring the voltage output of an ignition coil with a multimeter is a simple and effective way to test the ignition coil.
The following table shows the steps involved in measuring the voltage output of an ignition coil with a multimeter:
| Step | Description |
|---|---|
| 1 | Connect the positive lead of the multimeter to the positive terminal of the ignition coil. |
| 2 | Connect the negative lead of the multimeter to the negative terminal of the ignition coil. |
| 3 | Set the multimeter to the volts AC setting. |
| 4 | Crank the engine. |
| 5 | The multimeter should read the voltage output of the ignition coil. |
Interpreting the Dwell Time
What is Dwell Time?
The dwell time is the percentage of time that the ignition coil is powered on during each engine cycle. It is determined by the ignition timing, which is controlled by the engine’s computer. The dwell time is an important factor in ignition system performance, as it affects the amount of time that the coil has to build up a magnetic field.
Measuring Dwell Time with a Multimeter
To measure the dwell time, you will need to connect a multimeter to the ignition coil. The positive lead of the multimeter should be connected to the positive terminal of the coil, and the negative lead should be connected to the negative terminal.
Calculating Dwell Time from Duty Cycle
Once you have connected the multimeter, you can set it to measure the duty cycle. The duty cycle is the percentage of time that the ignition coil is powered on. The dwell time can be calculated from the duty cycle using the following formula:
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Dwell Time = Duty Cycle x 360 degrees
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Interpreting the Dwell Time
The dwell time for a typical ignition coil is between 5 and 10 degrees. If the dwell time is too short, the coil will not have enough time to build up a strong magnetic field, and the spark will be weak. If the dwell time is too long, the coil will overheat and could eventually fail.
The table below shows the dwell time for different types of ignition systems:
| Ignition System | Dwell Time (degrees) |
|---|---|
| Conventional | 5-10 |
| Electronic | 3-6 |
| Solid State | 1-2 |
If the dwell time is not within the specified range, it is likely that there is a problem with the ignition system. You should have the system diagnosed by a qualified mechanic.
Troubleshooting Open Circuits
To test for an open circuit, you need to remove the coil from the distributor. Use your multimeter to set it to the highest ohmic scale. Touch one probe to each terminal on the coil and observe the reading. An open circuit is indicated by an infinite resistance reading (OL).
An open circuit typically results from a broken wire inside the coil or a faulty connection between the coil and the distributor. Here’s a step-by-step troubleshooting guide:
- Check the primary circuit. Disconnect the coil from the distributor and use the multimeter to test the resistance between the positive terminal on the coil and the body of the distributor. A good primary circuit will read between 0.5 ohms to 2 ohms.
- Check the secondary circuit. Connect the multimeter to the positive and negative terminals on the coil. A good secondary circuit should read between 5,000 and 30,000 ohms.
- Check the coil’s continuity. Connect the multimeter to each terminal on the coil and observe the reading. A good coil will have continuity, meaning that there is a complete circuit between the two terminals.
- Inspect the wiring. Check the wiring harness for any loose or damaged connections. Ensure that all wires are securely attached to the coil and the distributor.
- Test the distributor. If the coil passes all the tests, the problem may be with the distributor. Test the distributor cap and rotor for cracks or damage. Replace the distributor if it fails the test.
- Check the ignition module. The ignition module can fail, causing an open circuit in the coil circuit. Use the multimeter to test the ignition module according to the manufacturer’s instructions.
- Replace the coil. If the coil fails any of the tests or if the problem persists after you have tested all the other components, replace the coil with a new one.
Identifying Short Circuits
To test for short circuits, set the multimeter to the ohms or continuity setting and connect the probes to the primary terminals of the ignition coil. A reading of zero ohms or a continuous beep indicates a short circuit. To further isolate the short, disconnect the ignition coil from the wiring harness and retest. If the short persists, it is likely in the ignition coil itself. If the short disappears, it is likely in the wiring harness or another component connected to the ignition coil.
Here is a table summarizing the steps for testing ignition coils for short circuits:
| Step | Action |
|---|---|
| 1 | Set the multimeter to the ohms or continuity setting. |
| 2 | Connect the probes to the primary terminals of the ignition coil. |
| 3 | Read the multimeter display. |
| 4 | If the reading is zero ohms or there is a continuous beep, there is a short circuit. |
| 5 | Disconnect the ignition coil from the wiring harness and retest. |
| 6 | If the short persists, it is likely in the ignition coil itself. |
| 7 | If the short disappears, it is likely in the wiring harness or another component connected to the ignition coil. |
Checking Terminal Connections
1. Inspect the coil’s terminals for any signs of damage or corrosion.
Make sure the terminals are clean and free of debris to ensure a good electrical connection.
2. Use the multimeter to check the resistance across the primary terminals.
The primary terminals are typically labeled with a “P” or “Prim.” The resistance value should be within the manufacturer’s specified range, typically around 0.5 to 5 ohms.
3. Check the resistance across the secondary terminals.
The secondary terminals are usually labeled with an “S” or “Sec.” The resistance value should be significantly higher than the primary resistance, typically in the range of 5,000 to 50,000 ohms.
4. Check the resistance between each terminal and the coil’s body.
Verify that there is no conductivity between the terminals and the coil’s body. This could indicate an internal short circuit within the coil.
5. Disconnect the coil from the vehicle’s electrical system.
This will prevent any electrical current from flowing through the coil while you’re performing the remaining tests.
6. Set the multimeter to the AC voltage scale.
The ignition coil produces alternating current (AC), so you need to use the AC voltage setting.
7. Attach one probe to the coil’s negative terminal and the other probe to the positive terminal.
Crank the engine and observe the voltage reading on the multimeter.
8. The voltage reading should be in the range of 5,000 to 20,000 volts.
If the voltage is too low or zero, there may be a problem with the coil, the ignition module, or the wiring.
9. If you have a spark tester, you can use it to test the coil’s ability to produce a spark.
Connect the spark tester to the coil’s output terminal and crank the engine. The spark tester should produce a bright spark if the coil is functioning correctly.
| Test | Expected Result | Indication of Problem |
|---|---|---|
| Primary resistance | 0.5 – 5 ohms | Open or shorted coil |
| Secondary resistance | 5,000 – 50,000 ohms | Open or shorted coil |
| Resistance to body | No conductivity | Internal short circuit |
| AC voltage (engine running) | 5,000 – 20,000 volts | Weak or faulty coil, ignition module, or wiring |
Interpreting Multimeter Readings
When testing ignition coils with a multimeter, the readings you obtain can provide insights into the coil’s condition. Here are some guidelines for interpreting these readings:
Open Circuit
If the multimeter reads “OL” or “Infinity,” it indicates that the ignition coil is open. This means that the circuit is broken and current cannot flow through the coil. The coil is likely faulty and requires replacement.
Shorted Condition
If the multimeter displays a reading close to zero ohms, it suggests that the ignition coil is shorted. The short circuit allows current to bypass the coil and flow directly through it. This condition can also lead to coil failure.
Primary Resistance
The primary resistance reading indicates the resistance of the primary winding of the ignition coil. This reading should typically fall within the manufacturer’s specifications (usually between 0.5 and 2 ohms). A high reading indicates a faulty winding, while a low reading may suggest a short circuit.
Secondary Resistance
The secondary resistance reading measures the resistance of the secondary winding of the ignition coil. This reading should also be within the manufacturer’s specifications (typically between 5,000 and 25,000 ohms). A high reading may indicate an open circuit, while a low reading may suggest a shorted winding.
Dwell Time
Dwell time refers to the amount of time that the ignition coil remains energized during each ignition cycle. This reading is not directly measured by a multimeter but can be calculated based on the dwell angle provided by a timing light. A shorter dwell time indicates a weaker ignition signal, while a longer dwell time may indicate a problem with the ignition system or engine timing.
How To Test Ignition Coils With A Multimeter
To test an ignition coil, you will need a multimeter. A multimeter is a device that can measure voltage, current, and resistance. You can find multimeters at most hardware stores.
Once you have a multimeter, follow these steps to test an ignition coil:
- Set the multimeter to measure resistance. The resistance setting will be abbreviated as “Ω”.
- Touch the positive lead of the multimeter to the positive terminal of the ignition coil.
- Touch the negative lead of the multimeter to the negative terminal of the ignition coil.
- Read the display on the multimeter. The resistance reading should be between 0.5 and 1.5 ohms.
If the resistance reading is not between 0.5 and 1.5 ohms, the ignition coil is probably bad and needs to be replaced.
People Also Ask About How To Test Ignition Coils With A Multimeter
Q: What is the function of an ignition coil?
Q: What is the function of an ignition coil?
An ignition coil is a transformer that converts the low voltage from the battery into the high voltage needed to create a spark in the spark plug.
Q: What are the symptoms of a bad ignition coil?
Symptoms of a bad ignition coil can include difficulty starting the engine, engine misfires, and poor fuel economy.
Q: How often should ignition coils be replaced?
Ignition coils typically last for 100,000 to 150,000 miles. However, they can fail sooner if they are exposed to excessive heat or moisture.
