How To Test Hei Distributor Module

How to Test a HEI Distributor Module: A Comprehensive Guide

Testing your vehicle's High Energy Ignition (HEI) distributor module is crucial for ensuring optimal engine performance and avoiding frustrating breakdowns. A faulty module can lead to misfires, poor starting, and even complete engine failure. This guide provides a step-by-step approach to diagnosing HEI module problems, saving you time and money on potential repairs.

Understanding the HEI Distributor Module

The HEI distributor module is the brains of your ignition system. It receives a signal from the engine's computer (or points in older systems) and uses this to control the timing and firing of the spark plugs. A malfunctioning module can disrupt this precise timing, leading to noticeable engine issues.

Common Signs of a Bad HEI Module

Before diving into testing, familiarize yourself with the symptoms of a failing HEI module:

• Misfiring: Rough running, sputtering, or hesitation during acceleration.
• Hard starting: Difficulty cranking the engine, requiring multiple attempts to start.
• No spark: Complete lack of ignition, preventing the engine from running.
• Erratic idle: Fluctuations in engine speed at idle.
• Check Engine Light: Illumination of the check engine light accompanied by relevant diagnostic trouble codes.

Testing Your HEI Distributor Module: A Practical Approach

Testing your HEI module involves several key steps and requires basic tools. Always disconnect the negative battery terminal before starting any electrical work.

1. Visual Inspection

Begin with a visual inspection of the module. Look for any obvious signs of damage such as:

• Physical damage: Cracks, burns, or melted components.
• Loose connections: Check all wiring connections for security and corrosion.
• Fluid leaks: Look for signs of oil or water intrusion.

Any of these issues can indicate a problem and might require replacement.

2. Resistance Testing (using a multimeter)

This step requires a digital multimeter (DMM) capable of measuring resistance in ohms.

• Identify the terminals: Locate the terminals on the HEI module. The specific terminals and their functions may vary slightly depending on the vehicle and module, so consult your vehicle's service manual for precise locations.
• Measure resistance: Follow your vehicle's manual to find specified resistance values for the different terminals. Compare your readings to these specifications. Significant deviations from the specified ranges often suggest a faulty module.
• Interpret results: Readings outside the acceptable range indicate a faulty component and require module replacement.

Important Note: Resistance readings alone aren't always conclusive. Further testing may be necessary.

3. Checking for Spark (using a spark tester)

A spark tester will help verify the module's ability to generate a spark.

• Connect the spark tester: This involves connecting the tester appropriately to the ignition coil wire and a ground point.
• Crank the engine: Crank the engine over while observing the spark tester.
• Observe the spark: A strong, consistent spark confirms proper module function. Weak or intermittent sparking indicates a problem.

Again, refer to your vehicle's service manual for the proper connection and testing procedures.

4. Advanced Diagnostics (using a scan tool)

For modern vehicles with advanced computer systems, a scan tool is invaluable. A scan tool can retrieve diagnostic trouble codes (DTCs) that may pinpoint a faulty HEI module or other related issues.

• Connect the scan tool: Connect the scan tool to your vehicle's OBD-II port.
• Retrieve DTCs: Retrieve and analyze the diagnostic trouble codes.
• Interpret results: Look for codes directly related to ignition problems.

Replacing the HEI Distributor Module

If your testing reveals a faulty HEI module, replacement is usually necessary. Remember to always follow the correct procedures outlined in your vehicle's service manual to ensure proper installation and prevent damage.

Disclaimer: This guide provides general information. Always consult your vehicle's repair manual for specific instructions and safety precautions related to your particular make and model. Improper testing or repair can lead to damage or injury.