The Ultimate Guide: How to Test GM HEI Ignition Coil for Optimal Car Functioning

The General Motors High Energy Ignition (HEI) system is a staple in many classic and modern vehicles, known for its reliability and performance. However, even the most robust systems can experience issues, and the ignition coil is a common culprit. If your engine is experiencing misfires, rough idling, or a lack of power, the HEI ignition coil might be the culprit. This blog post will guide you through the process of testing your GM HEI ignition coil to determine if it’s the source of your engine woes.

Understanding the HEI Ignition Coil

The HEI ignition coil is a crucial component in the ignition system, responsible for generating high voltage to ignite the spark plugs. When the ignition switch is turned on, the coil receives low voltage from the battery. This low voltage is then transformed into high voltage through the coil’s windings, creating a spark that travels to the spark plug, igniting the air-fuel mixture in the cylinder.

Common Symptoms of a Faulty HEI Ignition Coil

Before diving into the testing process, it’s essential to understand the common symptoms that signal a faulty HEI ignition coil:

• Misfiring: This is a common symptom of a faulty ignition coil, as it indicates that the spark plug is not receiving the necessary voltage to ignite the fuel.
• Rough Idling: The engine may idle unevenly or stall if the ignition coil is not functioning properly.
• Lack of Power: A weak or intermittent spark from a faulty ignition coil can cause a noticeable decrease in engine power.
• Engine Backfiring: A faulty ignition coil can lead to backfiring, which occurs when the air-fuel mixture ignites prematurely in the exhaust manifold.
• Difficulty Starting: A failing ignition coil may struggle to provide enough spark to start the engine.

Essential Tools for Testing the HEI Ignition Coil

To test your HEI ignition coil, you’ll need a few basic tools:

• Multimeter: This is an essential tool for measuring voltage, resistance, and continuity.
• Spark Plug Wire Tester: This tool helps you check for spark at the spark plug.
• Test Light: This tool is useful for verifying the presence of power in the ignition system.
• Safety Glasses: Eye protection is vital when working with electrical components.

How to Test the HEI Ignition Coil: A Step-by-Step Guide

Now, let’s get into the testing process. This guide will help you determine if your ignition coil is the source of your engine problems:

1. Visual Inspection: Begin by visually inspecting the HEI ignition coil for any signs of damage, such as cracks, burns, or corrosion. If you find any damage, it’s a strong indication that the coil needs to be replaced.

2. Resistance Test: Use your multimeter to measure the resistance of the ignition coil‘s primary and secondary windings. Locate the positive (+) and negative (-) terminals on the coil.

• Primary Winding: Connect the multimeter leads to the positive and negative terminals of the primary winding. A typical resistance reading for a primary winding should be between 0.5 and 2 ohms.
• Secondary Winding: Connect the multimeter leads to the positive terminal and the center terminal of the secondary winding. A typical resistance reading for a secondary winding should be between 8,000 and 12,000 ohms.

3. Voltage Test: With the ignition key in the “ON” position, but the engine off, measure the voltage at the positive terminal of the ignition coil. You should expect to see battery voltage (usually around 12 volts).

4. Spark Test: Disconnect the spark plug wire from the spark plug, and connect the spark plug wire tester to the spark plug wire. With the ignition key in the “ON” position, you should see a strong blue spark when you crank the engine.

5. Test Light Test: Connect the test light to the positive terminal of the ignition coil and ground the other end of the test light. Turn the ignition key to the “ON” position. The test light should illuminate, indicating that the coil is receiving power.

6. Continuity Test: Use your multimeter to check the continuity of the ignition coil’s primary and secondary windings. Connect the multimeter leads to the positive and negative terminals of the primary winding and then to the positive terminal and the center terminal of the secondary winding. You should get a continuity reading (a low resistance value) for both windings.

Troubleshooting and Replacement

If your HEI ignition coil fails any of these tests, it’s likely faulty and needs to be replaced. To replace the ignition coil, follow these steps:

1. Disconnect the battery terminals to prevent electrical shock.
2. Locate the HEI ignition coil and disconnect the spark plug wire and the electrical connector.
3. Remove the bolts or screws holding the ignition coil in place.
4. Install the new ignition coil, ensuring the connector and spark plug wire are properly connected.
5. Reconnect the battery terminals and start the engine.

Final Thoughts: Ensuring Optimal Performance

By following these steps, you can effectively test your HEI ignition coil and determine if it’s the root of your engine problems. Remember, a faulty ignition coil can significantly impact your engine’s performance, so addressing the issue promptly is crucial.

Information You Need to Know

1. How often should I replace my HEI ignition coil?

While HEI ignition coils are known for their durability, they can wear out over time. It’s generally recommended to replace them every 50,000 to 100,000 miles, or sooner if you notice any of the symptoms mentioned above.

2. Can I test the HEI ignition coil with the engine running?

It’s not recommended to test the HEI ignition coil with the engine running. This could expose you to dangerous electrical currents and potentially damage the coil.

3. What if my HEI ignition coil tests good, but my engine still has problems?

If your ignition coil tests good, other components in the ignition system, such as the distributor, spark plugs, or wiring, could be the culprit. You’ll need to continue troubleshooting to identify the problem.

4. Can I use a generic ignition coil instead of an HEI coil?

It’s not recommended to use a generic ignition coil in place of an HEI coil. HEI coils are designed specifically for the HEI system and may not function properly in other systems.

5. What are some signs that my distributor might be faulty?

If your engine is misfiring, experiencing a loss of power, or having difficulty starting, the distributor could be the issue. Other signs include a worn or damaged rotor, a faulty cap, or a leaking vacuum advance.