Troubleshooting GM's HEI Ignition System

To understand Electronic Ignition and how the ignition system couples to the computerized engine management system, you must troubleshoot an electronic ignition distributor system.

The particular distributor you will be using in the laboratory was used in Chevrolet V8 engines from 1974 through 1985 cars and trucks. This High Energy Ignition (HEI) technology is still in use in current GM ignition systems.

The Delco-Remey HEI system consists of the battery, ignition switch, ignition coil, spark plugs, primary and secondary wiring and a special distributor assembly.

Full battery voltage is present at the battery terminal of the distributor in either the "START" or "RUN" position,as no ballast resistance wire is used.

This figure shows the exploded view of your project distributor.

Courtesy of General Motors Corporation

This testing is used when the ignition has no available spark and the "BATT" wire has been checked for battery voltage in START and RUN. 

After you have disassembled your distributor, you will be testing the electrical parts of the system. You may also use references from General Motors, or from Mitchell Manuals, or Mitchell on Demand all found in the laboratory.

First test the ignition coil primary, as shown in the figure below. The normal specifications should be between 0.5ohms to 4.0ohms.

Second test the ignition coil secondary, as shown in the figure below. The normal specification should be between 4Kohms to 14Kohms.

Next, check to see that the primary coil does not have any continuity to ground. By checking from the ground terminal to either of the primary coil connections,  "Tach"  or  "Batt"  ohm meter should read, infinity or "OL"

Courtesy of General Motors Corporation

If the Ignition Coil checks out as good, it should still be tested with a performance test using an Oscilloscope under load, but we will do this after the system is returned to service and can be performance tested with an ignition analyzer.

Next, the pick up coil must be tested, check with an Ohmmeter use the two leads from the coil beneath the pole piece. The specifications are 500ohms to 1500ohms, you must flex the wires and operate the vacuum advance while testing, the reading should remain stable through the test. If not replace the pick up coil.  While the Ohmmeter is connected to one side of the pick up coil connect the other lead to the body ground of the distributor housing the reading should read Infinity or "OL", if not replace the pick up coil. See the figure below.

Courtesy of General Motors Corporation

If after these tests the ignition system will not create a spark replace the Ignition Module.

                                                                                               "Mac" 10/11

This exercise has allowed you to witness the first and current process of testing control modules in electronic module systems including all computer systems. An inherent problem exists; if you make any mistakes or skip any steps you will find the module at fault and mistakenly replace it without repairing the failure.

Please post your response to; How will you overcome or protect you and your paying customer from replacing good modules or computers?  Add your name and class to your response to comments below. 

This project meets the requirements of the State of California Career Technical Education Model Curriculum Standard C6.0; Students understand the application, operation, maintenance, and diagnosis of engines. C6.4 Maintain, diagnose, service, and repair ignition, electronic, and computerized engine controls and fuel management systems.