HEI System - Description and Diagnosis Chart
No. T-36February, 1978
The High Energy Ignition System (HEI)
In 1974 General Motors began equipping passenger cars and light trucks with an electronic ignition system called High Energy Ignition (HEI). The HEI is different in many ways from the previously standard breaker-point ignition system.
^ Higher available secondary voltage of 35,000 volts.
^ The secondary spark plug wires are larger diameter with silicone rubber insulation. This type of wire minimizes cross firing or arching between wires. The silicone insulation is softer than rubber insulation, so wires should be routed to avoid chafing on the engine or accessories. The insulation should never be punctured with sharp tools. The boots fit tightly on the spark plug insulators and are thus sometimes difficult to remove from the spark plugs. Tools are available from several tool companies to make removal easier.
^ Distributor cap and rotor are made of special material to handle the higher secondary voltage.
^ An internal condenser is for reducing radio interference and is not a normal replacement item.
^ There is no resistance wire or ballast resistor between the ignition switch and the coil. The system operates on full battery voltage.
^ The ignition coil is mounted in the distributor cap on most engines. Figure 1.
^ Some 4-cylinder and L-6-cylinder ignition coils are mounted outside of the distributor but are different in appearance from previously standard ignition coils.
^ Breaker points are no longer used, so point maintenance and replacement is eliminated. Instead of breaker points, a magnetic pickup and an electronic module are used. Figure 3.
^ The connector on the distributor includes a spade terminal for connecting a service tachometer. Some tachometers should be connected to this terminal and ground, others to battery positive, some will not work at all. Refer to manufacturer's instructions for the equipment used. A spade terminal female connector with the wire-end bent 90° makes a simple adapter for connecting a tachometer. The tachometer terminal on the distributor cap must never be grounded. This could damage the electronic circuitry of the module.
^ Distributors with the integral coil have no external secondary connections to attach a pickup for an oscilloscope. An inductive pickup that fits the top of the distributor cap must be used to pick up secondary impulses from the coil. Refer to the manufacturer's instructions for the equipment used. Secondary pickup on distributors with separate coil is the same as standard ignition systems.
^ Oscilloscope patterns from an HEI System may vary among different makes of oscilloscopes. Check the manufacturer's published patterns when using an oscilloscope.
Diagnosis
For diagnosis of the HEI System, follow the charts with the appropriate heading for the problem being experienced. These charts cover problems in the ignition system only. Do not overlook other systems such as fuel and carburetion, valves, engine compression, etc., that might cause the same complaint.
A High Energy Ignition Analyzer J-24642 is available from:
Kent-Moore Tool Division
28635 Mound Road
Warren, Michigan 48092
If this tester is available, it should be used to determine if the module needs replacing. Operating instructions are provided with the tester.
The calibrated spark gap tester used in these procedures is available from Kent-Moore Tool Division (J-26792) as well as AC-Delco outlets (ST-125).
DIAGNOSIS CHARTS
Introduction
Decision Trees And Tables:
Typical Symbols Used In Diagnostic Charts:
This section presents a systematic method of diagnosing and troubleshooting the High Energy Ignition system. The charts you will be using are different from the ones you have used before. They aren't "go - no go" decision trees or tables. Instead the new diagnosis and troubleshooting charts use pictures plus a few words to help you solve a problem, and symbols have replaced words.
Using the Charts
The charts are divided into three sections: step, sequence and result.
A sequence could be checking the battery lead terminal on the distributor. Each sequence ends with a result and tells you the next step to go to. Work through each step of the diagnosis and trouble-shooting charts until the system is repaired.
To find where parts are located in the system just look at the parts locator chart:
Engine Cranks But Will Not Start Or Runs Rough Or Cuts Out:
Engine Cranks But Will Not Start (Continued):
Engine Cranks But Will Not Start (Continued):
Problem: Engine Cranks But Will Not Start Or Runs Rough Or Cuts Out (Separate Coil)
Problem: Engine Cranks But Will Not Start Or Runs Rough Or Cuts Out (Integral Coil)
Engine Cranks But Will Not Start Or Runs Rough (Separate Coil):
Tools Required:
Engine Cranks But Will Not Start Or Runs Rough Or Cuts Out - Integral Coil:
Engine Cranks But Will Not Start (Continued):
Engine Cranks But Will Not Start (Continued):
Step/Sequence: