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.

Computer Management and Scanning the Vehicle

Computer Management System

Checking Codes and Analyzing Data

Courtesy of Snap-On Tool Corporation

When the Malfunction Indicator Warning Indicator or Service Vehicle Soon indicator and a whole host of other dash indicator lamps illuminate on the instrument panel, it is time to bring out the scan tool to give us an indication of what the problem may be.  The analyzer that we will focus on in this course is the Ethos scanner made by Snap-On Corporation. This scan tool is a first step scanner. We will be able to read codes in any module system and also read data that is generated by the computer system. To get further specific training from Snap-On you can visit the Snap-On website and sign on as a guest. Click on this hyperlink to bring you to their website.

http://www1.snapon.com/diagnostics

Use this hyperlink to take you to their training video covering the Ethos scan tool.

ETHOS SCANNER  

This hyperlink will take you to Snap-On’s power point training slide showing the depth training program. Use this training to get step by step understanding of all the specifics about the Ethos scanner. This set of slides will contain the questions to the in class test at the end of the course.   

ETHOS Scanner Training

Laboratory Exercise

1.      After viewing the Snap-On video and completing the Ethos Scanner Training slide show, secure a vehicle from our fleet with the instructor’s guidance or provide a vehicle of your own with the consent and guidance of your instructor.

2.      Complete the repair order that has been pre-written for this procedure; note the directions and questions in the technician notes area.

3.      Using the scan tool, scan the vehicle data and complete the data section on the repair order.

4.      Using the scan tool scan for any active codes, if there is an indicator on there will usually be at least one active code.

5.      Further scan the vehicle for any historical codes; note these codes on the technician notes area clearly marking them as historical.

6.      When you have found the code, use the information system in the lab to find the written information for code diagnosis.

7.      Follow the instructions to diagnose the code and find the failure of the computer management system.

8.      Show the instructor the steps you used to find the failure of your vehicle.

9.      Use the scan tool to clear all codes. Re-test vehicle for any codes returning after a test drive.

10.  Repair the vehicle; complete the repair order, including charges for labor and parts, turn in your repair order.

11.   Return the vehicle to the fleet parking lot.

                                                                                          "Mac" 10/11

Compression Testing an Engine

1.  Please read this entire article about analyzing engines.

2.  When you have completed the article, I want you and your team to choose one of the laboratory vehicles or a live job with the instructors approval, and complete the engine evaluation.

3.  Complete the Repair order and furnish it and the technician notes to the instructor for evaluation. For help follow these guidelines click url for help.
Repair Order Writing NU
4. Finally, post your own findings, including your final analysis, problems you encountered and what you learned about the engine analysis process. Post your comment by clicking on the comments listing at the end of this article.

                                                                                       

Compression and Leakage Testing Notes            

When compression or leakage testing an engine the engine should be warm with a fully charged battery, and the throttle plate blocked open for full air flow. 

          The result specifications will vary by what you are testing for and if you are working for a manufacturer considering warranty returns.  You must follow these specifications to be in compliance with your employer. Usually between 15% for High Performance and as low as 30% for Low Performance/Utility.  In my Independent shop, I personally followed these specifications while working for my customers and they were quite content with my outcomes and charges for that work.  A well running engine had all cylinders within 20% of one another, and 20% maximum leakage. 

Compression Testing

A difference of more than the 15% Performance to 30% Utility would be a major concern.  All spark plugs removed.  The first pressure impulse would be normally at least 50% of the final reading.  Since 1997 nationally, 4 impulses should be the normal amount of cranking during testing (Aspire, DCA/BAR 1996).

Wet Testing a Failing Cylinder

For gasoline engines that have failing cylinders a wet test and identify top end problems (Valves) or bottom end problems (Rings).  This test is a quick test that does a fair job of identification.  A preferable test is the Leakage test.  Use a small amount of oil injected into the cylinder, 2 squirts of an oil squirt can through the spark plug hole. (Not on diesel engines)  A substantial increase in pressure will indicate failing rings, by artificially sealing the rings temporarily to the cylinder wall.

Cylinder Leakage Testing

The Cylinder Leakage Tester in conjunction with a Compression test is an excellent way to diagnose specific failures in a cylinder.  I personally choose to remove only one plug at a time, Snap-On likes to remove all plugs at once to hear leaks through adjacent cylinders, head gasket was however checked during the compression test. Absolutely new engines leak at 7%, broken in new engines leak at 4%, maximum leakage below 15% Performance, and 30% Utility, depending on customer is allowable.                

                                                                                      “MAC” 7/11

To "Dead" time an engine with a distributor, Notes from "MAC"

DEAD TIMING AN ENGINE

Any time you remove a distributor you must return it and expect it to deliver a spark at the right place at the right time!

Procedure “A”

This procedure means that you have taken the time to mark the distributor rotor and distributor body before you have removed the distributor.  You can simply return the distributor to the same location and expect the engine to run as it ran before you started.  If you are installing a replacement distributor or have done repairs to the distributor you removed you will still need to time the engine with a timing light or scan tool.

Procedure ”B”

This procedure is required if the distributor was removed without marking it first or if the engine was rotated while the distributor was out of the vehicle.  (Watch out for your “Friends” when your back is turned!)

1. Remove cylinder #1 spark plug, with your thumb plugging the spark plug hole crank the engine and stop when you get the blast of air pushing your thumb off the hole. This indicates Top Dead Center Compression Stroke, rotate the engine slightly to establish the rotating timing mark to the stationary timing mark.      You have successfully found TDC compression stroke.
2. Locate the Firing Order, direction of rotation of the distributor, and location of the number one spark plug wire connection in the distributor.  Service information can provide these specifications.
3. Install the distributor, locate the rotor position exactly where the rotor is required to be indexed.  (Fuel injection, and timing are inter-related at this location on many engines)  Be certain the distributor has indexed with the oil pump drive and loosely install the distributor hold down bolt and bracket.
4. Install #1 spark plug wire and continue installing the rest of the spark plug wires following the proper rotatation and firing order, install the coil wire.
5.  Attempt to start the engine, Safety must be observed, engine should start and run adjust the general timing to the “Best running condition” by turning the distributor body to the best location.
6. Turn off the engine and install the timing light, on later engines the scan tool, Set the ignition timing to the manufacturer’s specifications.
7. At this time you should verify the rotational advance device (engine speed) and engine load (Power) device for advancing ignition timing.

                                                                                                                  “MAC” 7/11