Every car owner has, at some point, experienced the frustration of a car that just won’t start. While there are many potential causes for this, one of the most common is a faulty distributor coil. The distributor coil is a small, but essential, component of the ignition system. It is responsible for converting the low-voltage current from the battery into the high-voltage current needed to create a spark at the spark plugs. If the distributor coil is not working properly, the engine will not be able to start, or may run erratically.
There are a few simple steps you can take to check the distributor coil. First, locate the coil. It is usually mounted on the side of the distributor, which is located at the front of the engine. Once you have found the coil, disconnect the wires that are connected to it. Next, use a multimeter to measure the resistance of the coil. The resistance should be between 0.5 and 2 ohms. If the resistance is too high or too low, the coil is faulty and will need to be replaced.
If the resistance of the coil is within the normal range, the next step is to test the coil’s output voltage. To do this, connect the positive lead of the multimeter to the positive terminal of the coil and the negative lead to the negative terminal. Then, crank the engine over. The multimeter should read between 12 and 15 volts. If the output voltage is too low or too high, the coil is faulty and will need to be replaced.
Identifying Malfunctioning Distributor Coil Symptoms
A distributor coil, also known as an ignition coil, is an essential component of the vehicle’s ignition system. It plays a vital role in converting the low-voltage electrical current from the battery into high-voltage sparks that ignite the air-fuel mixture in the engine’s cylinders. When a distributor coil malfunctions, it can lead to a range of performance issues and engine problems.
Here are some common symptoms that may indicate a faulty distributor coil:
1. Engine Misfiring or Rough Idling:
A weak or failing distributor coil can cause the spark to be intermittent or weak, leading to misfiring. This can result in noticeable irregularities in the engine’s idle and overall performance, creating a rough and uneven running condition.
2. Hard Starting or Engine Cranking Issues:
A malfunctioning distributor coil can make it difficult to start the engine or prevent it from cranking altogether. This happens because the ignition system is not receiving the sufficient voltage to create a strong spark for ignition.
3. Reduced Engine Power and Acceleration:
A weak spark from a faulty distributor coil can reduce the engine’s power and acceleration capabilities. This is because the cylinders are not receiving the optimal ignition timing and spark strength, resulting in lower performance and reduced efficiency.
4. Stalling or Surging While Driving:
Intermittent or weak spark caused by a failing distributor coil can lead to stalling or engine surges while driving. This can occur when the ignition system fails to generate a consistent spark, causing the engine to either shut off or operate erratically.
5. Engine Knocking or Pinging:
Severely weakened distributor coils can result in pre-ignition or detonation in the engine, which manifests as knocking or pinging sounds. This occurs when the air-fuel mixture ignites too early due to the weak spark, causing abnormal combustion and engine damage.
It’s important to note that these symptoms can also be caused by other ignition system components, such as spark plugs, ignition module, or wiring issues. Therefore, it’s essential to conduct thorough diagnostics to determine the exact cause of the issue and avoid costly repairs.
Visual Inspection of the Coil for Damage or Corrosion
Begin by carefully examining the distributor coil for any physical damage, such as cracks, dents, or broken wires. Look for visible signs of corrosion or rust on the housing or terminals, which could impede electrical contact and affect coil performance.
External Condition Assessment
The table below summarizes the key visual inspection points for the distributor coil:
| Inspection Point | Indication of Damage/Corrosion |
|---|---|
| Coil housing | Cracks, dents, or warping |
| Terminals | Rust, corrosion, or loose connections |
| Wires | Breaks, fraying, or exposed conductors |
If any signs of damage or corrosion are present, it is advisable to proceed with further testing to determine the extent of the issue and assess whether coil replacement is necessary.
Checking Coil Resistance Using a Multimeter
The third step to checking the distributor coil involves measuring its resistance. Use a multimeter to obtain accurate readings. Begin by connecting one probe of the multimeter to a contact point on the coil and the other probe to the ground. Set the multimeter to ohms (Ω) and record the resistance value displayed on the screen.
Here’s a table summarizing the typical resistance ranges for distributor coils:
| Ignition Coil | Resistance Range |
|---|---|
| Primary Coil | 0.4 – 1.5 Ω |
| Secondary Coil | 5,000 – 15,000 Ω |
If the measured resistance falls within these ranges, the coil is functioning properly. However, if the resistance is significantly lower or higher than the specified range, it may indicate a faulty coil that requires replacement.
Testing Distributor Output with a Spark Tester
A spark tester is a tool used to check the output of a distributor coil. It is a simple device that consists of a spark plug and a wire. To use a spark tester, simply connect the wire to the positive terminal of the battery and the spark plug to the distributor cap. Then, crank the engine and observe the spark. If there is no spark, then the distributor coil is not functioning properly.
There are a few things to keep in mind when using a spark tester. First, make sure that the spark plug is clean and in good condition. A dirty or damaged spark plug can prevent the spark from being visible. Second, make sure that the wire is securely connected to the battery and the spark plug. A loose connection can also prevent the spark from being visible.
If you are not comfortable using a spark tester, you can take your vehicle to a mechanic to have the distributor coil tested. A mechanic will have the proper tools and knowledge to diagnose the problem and recommend the best course of action.
| Here are some additional tips for using a spark tester: |
| – Use a spark tester with a built-in resistor. This will help to protect the ignition system from damage. |
| – Hold the spark tester away from the engine when cranking. This will prevent the spark from arcing to the engine and causing a fire. |
| – If you are not sure how to use a spark tester, consult a mechanic. |
Measuring Coil Primary Voltage with an Oscilloscope
Using an oscilloscope to measure the coil primary voltage is a more advanced method that provides a detailed view of the electrical signal. Here’s how to do it:
Equipment Required:
- Oscilloscope
- Coil wiring diagram
- Ignition coil
- Test leads
Procedure:
1. Connect the oscilloscope to the primary terminals of the coil using the test leads.
2. Set the oscilloscope to an appropriate time base and voltage scale.
3. Start the engine and observe the waveform on the oscilloscope display.
4. The coil primary voltage should be around 12-14 volts when the engine is running.
5. Look for any abnormalities in the waveform, such as:
| Waveform Characteristic | Possible Cause |
|---|---|
| No waveform | Open circuit in the coil primary winding or wiring |
| Low voltage | Weak coil, bad wiring connections, or insufficient battery voltage |
| High voltage | Damaged or shorted coil |
| Unstable waveform | Intermittent connection or faulty ignition module |
| Spikes or noise | Coil insulation breakdown or faulty ignition components |
Troubleshooting Coil Ground and Power Connections
Checking Ground Connections
Perform these steps to check the ground connections:
- Clean and reconnect all ground connections at the battery, starter, and distributor.
- If the problem persists, use a multimeter to check for continuity between the negative battery terminal and the distributor body.
- Continuity should be present, indicating a good ground connection.
Checking Power Connections
Follow these steps to check the power connections:
- Turn the ignition key to the “ON” position without cranking the engine.
- Use a multimeter set to the voltage scale to check for power at the positive terminal of the coil.
- There should be voltage present, typically around 12 volts.
Further Troubleshooting Steps
If the ground and power connections are confirmed to be good, but the coil still doesn’t operate properly, consider the following additional troubleshooting steps:
| Component | Test | Expected Result |
|---|---|---|
| Coil Resistance | Check coil resistance per manufacturer specifications | Within specified range |
| Rotor | Inspect for wear or damage | Smooth and undamaged |
| Distributor Cap | Check for cracks or carbon tracking | Clean and in good condition |
If any of these components fail the test, replace them accordingly to resolve the coil issue.
Verifying Ignition Control Module Compatibility
The ignition control module (ICM) is responsible for controlling the timing of the spark plugs in an ignition system. It is typically mounted on or near the distributor and receives input from the crankshaft position sensor and the camshaft position sensor. The ICM then uses this information to calculate the correct timing for the spark plugs.
When an ICM fails, it can cause a variety of problems, such as engine misfires, stalling, and difficulty starting. If you are experiencing these problems, it is important to check the compatibility of the ICM with your vehicle.
How to Check Distributor Coil Compatibility
- Locate the distributor cap. It is typically located on the top of the engine and has a round or oval shape.
- Remove the distributor cap by pulling it straight up.
- Locate the distributor coil. It is typically located in the center of the distributor and has a cylindrical shape.
- Disconnect the electrical connectors from the distributor coil.
- Remove the distributor coil by pulling it straight up.
- Compare the old distributor coil to the new one. They should be the same size and shape.
- Check the resistance of the distributor coil. It should be within the specifications listed in the vehicle’s service manual.
- If the resistance of the distributor coil is not within specifications, it should be replaced.
| Symptom | Possible Cause |
|---|---|
| Engine misfires | Faulty distributor coil |
| Stalling | Faulty distributor coil |
| Difficulty starting | Faulty distributor coil |
Inspecting Coil Harness and Wiring for Shorts or Opens
Before removing the distributor cap, visually inspect the coil harness and wiring for any signs of damage, such as:
- Cuts or abrasions in the insulation
- Loose or disconnected connectors
- Corrosion or rust on the terminals
Any of these conditions can cause electrical shorts or opens, which can affect the ignition system’s performance.
Checking for Shorts Using an Ohmmeter
To check for shorts in the coil harness, use an ohmmeter set to the lowest resistance scale. Connect one lead of the ohmmeter to the positive (+) terminal of the ignition coil, and the other lead to the negative (-) terminal. The ohmmeter should read an open circuit (infinite resistance).
If the ohmmeter reads a low resistance, there is a short circuit somewhere in the harness. Follow the harness carefully, looking for any signs of damage or shorts to ground.
Repeat the test by connecting the ohmmeter to the other end of the coil harness, at the distributor cap. The ohmmeter should still read an open circuit.
If the ohmmeter reads a short circuit, there is a problem with the distributor cap or the wiring inside it. Remove the cap and inspect it carefully for any damage, such as cracks or signs of carbon tracking. If necessary, replace the distributor cap.
To check for opens in the coil harness, set the ohmmeter to the highest resistance scale. Connect one lead of the ohmmeter to the positive (+) terminal of the ignition coil, and the other lead to the negative (-) terminal. The ohmmeter should read a low resistance (usually less than 1 ohm).
If the ohmmeter reads an open circuit, there is an open circuit somewhere in the harness. Follow the harness carefully, looking for any signs of damage or broken wires. If necessary, repair or replace the coil harness.
Diagnosing Faulty Distributor Coil
To diagnose a faulty distributor coil, inspect the coil for any visible signs of damage, such as cracks, burns, or loose connections. You can also use a multimeter to check the coil’s resistance. The resistance should be within the manufacturer’s specifications. If the resistance is too high or too low, the coil is likely faulty and needs to be replaced.
Checking the Distributor Cap
To check the distributor cap, remove it from the distributor and inspect it for any cracks, burns, or loose connections. You can also use a multimeter to check the cap’s resistance between the terminals and the center contact. If the resistance is too high or too low, the cap is likely faulty and needs to be replaced.
Checking the Rotor
To check the rotor, remove it from the distributor and inspect it for any cracks, burns, or loose connections. You can also use a multimeter to check the rotor’s resistance between the terminals and the center contact. If the resistance is too high or too low, the rotor is likely faulty and needs to be replaced.
Replacing the Distributor Cap and Rotor
To replace the distributor cap and rotor, follow these steps:
- Disconnect the negative battery terminal.
- Remove the distributor cap and rotor.
- Install the new distributor cap and rotor.
- Connect the negative battery terminal.
- Start the engine and check for proper operation.
Checking the Ignition Coil
To check the ignition coil, you will need a spark tester. Connect the spark tester to the spark plug wire and start the engine. If there is no spark, the ignition coil may be faulty and needs to be replaced.
Checking the Spark Plugs
To check the spark plugs, remove them from the engine and inspect them for any wear or damage. You can also use a spark plug tester to check the plugs for proper spark. If the plugs are worn or damaged, they need to be replaced.
Checking the Ignition Wires
To check the ignition wires, inspect them for any cracks, burns, or loose connections. You can also use a multimeter to check the wires’ resistance. If the resistance is too high or too low, the wires may be faulty and need to be replaced.
Reinstalling Distributor Coil and Verifying Proper Ignition
Once the distributor coil has been tested and found to be faulty, it should be replaced with a new one. Here are the steps on how to reinstall the distributor coil and verify proper ignition:
1. Disconnect the negative battery terminal
To ensure safety, it is important to disconnect the negative terminal of the battery before removing or installing any electrical components.
2. Remove the old distributor coil
Locate the distributor cap and remove it by unfastening the retaining bolts. Once the cap is removed, you will see the distributor rotor and coil. Disconnect the wires from the coil terminals and remove the mounting bolts to take out the old coil.
3. Install the new distributor coil
Align the new distributor coil with the mounting holes and secure it with the bolts. Reconnect the wires to the coil terminals, making sure the connections are snug.
4. Install the distributor cap
Place the distributor cap back onto the distributor housing and tighten the retaining bolts. Ensure that the cap is securely fastened.
5. Reconnect the battery
Reconnect the negative terminal of the battery to restore power to the vehicle.
6. Start the engine and check for proper ignition
Start the engine and listen for any unusual noises or vibrations. If the engine starts smoothly and runs without any issues, then the distributor coil has been installed correctly and the ignition system is functioning properly.
7. Check for any error codes
After verifying the proper ignition, it is advisable to check for any error codes that may have been stored in the vehicle’s computer during the repair process. This can be done using an OBD-II scanner.
8. Road test the vehicle
Take the vehicle for a short road test to assess its performance under real-world conditions. Ensure that the engine runs smoothly at various RPMs and that there are no hesitations or misfires.
9. Re-check the distributor coil after driving
After the road test, re-check the distributor coil to ensure that it is still functioning properly. Look for any signs of overheating or damage, and make sure the connections are secure.
10. Monitoring Distributor Coil Performance Over Time
It is recommended to periodically inspect the distributor coil and its connections to ensure continued proper ignition. Signs of a failing distributor coil may include difficulty starting, engine stalling, hesitation during acceleration, or decreased engine performance. If any of these issues arise, it is advisable to have the distributor coil and ignition system checked by a qualified mechanic.
| Symptom | Possible Cause |
|---|---|
| Engine hard to start or won’t start | Faulty distributor coil |
| Engine stalls | Poor electrical connection or damaged distributor coil |
| Hesitation during acceleration | Weak or failing distributor coil |
| Decreased engine performance | Diminished spark output from distributor coil |
How To Check Distributor Coil
Materials:
- Multimeter
- Test light
Steps:
1. Disconnect the negative battery terminal.
2. Locate the distributor coil. It is usually a cylindrical-shaped component mounted on the side of the distributor.
3. Disconnect the wires from the coil.
4. Set the multimeter to ohms.
5. Touch one probe to each terminal on the coil.
6. The multimeter should read between 0.5 and 1.5 ohms. If the reading is outside of this range, the coil is faulty.
7. Reconnect the wires to the coil.
8. Reconnect the negative battery terminal.
9. Start the engine.
10. Touch the test light to the positive terminal on the coil.
11. The test light should light up. If it does not, the coil is faulty.
People Also Ask
How do I know if my distributor coil is bad?
Symptoms of a bad distributor coil include:
* Engine misfires
* Hard starting
* Reduced engine power
* Fuel economy problems
How often should I check my distributor coil?
You should check your distributor coil every 30,000 to 50,000 miles.
Can I replace a distributor coil myself?
Yes, you can replace a distributor coil yourself. However, it is important to follow the manufacturer’s instructions carefully.
