Secondary Testing for Waste Spark/Distributorless Ignition Systems

16-06 Explore distributorless ignition system testing procedures.

Spark systems require an adapter to diagnose the secondary side of the system. There are two methods to test the system. Use a capacitive pickup on each HT wire with a mixing adapter displays all the cylinders on a single screen. If an ignition adapter is not available using a universal capacitive tester such as the Wyze Probe, or its equivalent, will test each cylinder individually.

Using a Scope to Test Distributorless Ignition Systems

If an ignition adapter is being used, follow the manufacturer’s recommended operating procedures.

• Connect a capacitive probe to each spark plug wire following the manufacturer’s instructions.
  • Or use a universal capacitive probe on each coil individually
  • The capacitive probe is attenuated to protect the scope from high secondary voltage
• Start the engine.
• Input the scope’s kV and time base settings.
• Use the initial settings—parade pattern:
  • Use 5 kV/Div and 10 ms/Div to see firing kV.
  • Use 1 kV/Div and 2 ms/Div to zoom in on the spark line or for single-cylinder testing.
  • Adjust scope as necessary to obtain the detail needed.
• Compare the waveforms.
  • If the parade pattern is used, all the cylinders will be displayed on one screen, making comparison easier (FIGURE 16-30).
  • If the universal probe is being used, note any differences between cylinders. Take a snapshot or video to help with analysis.
• Keep in mind the average waste spark/DIS operating values:
  • Firing voltage/kV demand typically averages between 10 and 15 kV on compression and between 3 and 4 kV on the exhaust or waste spark firing.
  • Spark kV averages between 1 and 4 kV.
  • Spark duration, also known as burn time or spark duration, should average between 1.0 and 2.0 ms. Most will average between 1.2 and 1.5 ms.

FIGURE 16-30 A DIS parade waveform from using a Snap-on scope and an SIA 2000 ignition probe. The probe was initially designed for waste spark systems but is also compatible for use with flag adapters, COP adapters and coil-on-coil in cap adapters. When using this ignition probe, determine which cylinders fire negative and which fire positive. In any waste spark system, half the cylinders will always fire in a positive (traditional) direction, and the other half will fire in a negative direction. The negative fired plugs will have a higher firing voltage then the positive fired plugs. The parade pattern shows the variation in the firing kV between cylinders. The added blue dotted line helps to illustrate the difference. The three cylinders that fire in a positive direction are at a lower voltage at about 9 kV. The other three cylinders, firing in a negative direction, are averaging approximately 14 kV.

Also note Channel 1, the yellow trace, shows much higher firing kV for all the cylinders compared to the cylinders on Channel 2, the green waveform. The difference in firing kV is because the spark plugs on Channel 1 (yellow trace) are firing on the power stroke, and the spark plugs on Chanel 2 (green trace) are firing on the exhaust or waste stroke. Firing under compression always requires more coil energy than a cylinder that is not under pressure.

Displaying the power and waste spark waveforms for comparison on the same screen is a handy diagnostic tool. If the waste spark firing voltage ever equals the power stroke firing voltage, suspect a concern with an open plug wire or spark plug. Recall that under normal operating conditions, the plugs firing on the power stroke should fall in an average range of 10 to 15 kV, while the exhaust firing voltage is typically 1 to 4 kV. The open creates an air gap larger than the spark plug gap, demanding more of the coil’s energy to overcome the additional resistance. The increased coil output results in a high firing kV for the at-fault cylinder, easily seen on the exhaust stroke’s firing line. In this screenshot, the firing kV of the misfiring cylinder (blue circle) is equal on both the power and waste spark events, around 9 kV, indicating an open in the secondary circuit.

Notice in the Profile section of the scope screen that the yellow waveform is inverted while the green waveform is not. Plugs firing on the exhaust stroke are already inverted since they fire from negative to positive. Be careful when viewing the waveform with both channels in use. Pay close attention to the voltage scales and the waveform for that channel. At a quick glance, it is easy to apply the wrong voltage level to a waveform.

Using a Scope to Test Coil-on-Plug Systems

Although there are still a sizable number of DIS systems, and to a lesser extent distributor ignition system, COP is the most prominent. The scope, once an indispensable tool for older ignition systems, has lost some of its value for use on COP systems with technicians. COP applications lend themselves well to scope testing and are invaluable for hard to diagnose concerns while shortening “everyday troubleshooting” procedures. Use a DSO if one is available. The following scope tests are available:

• Measure the primary waveform on a two-wire COP.
  • The primary waveform is a lower voltage duplicate of the secondary waveform.
  • The coil primary cannot be seen in multi-wire (three- and four-wire) coil applications.
• Measure primary current with a scope and amp clamp on any COP or other type of ignition system.
• The scope is the best way to find intermittent or hard to diagnose concerns.
  • Install a power brake:
    • To prevent personal injury when power braking, ensure that the parking brake is engaged, block the drive wheels with appropriate wheel chocks, and make sure no one is standing in front of or behind the vehicle while performing the test.
  • Test-drive the system, using extended scope test leads, with the assistance of another technician (FIGURE 16-31).

FIGURE 16-31 Aftermarket equipment suppliers offer extended length test leads for various scopes from AESwave.com. The leads shown on the left are 5 feet in length with BNC connectors for the Pico Scope, and the leads on the right are 10 feet long with banana plugs for the Snap-on scope. Extended length leads for other scopes are also available. These cables are fully shielded and allow technicians to take their scopes with them, along with another technician, to actively monitor the ignition system or any other component during a test drive.

Secondary Testing for Coil-on-Plug Systems

The testing procedure for COP ignition systems is slightly different than that for distributor and waste spark ignition systems, where all the cylinders can be checked simultaneously. Instead, secondary system testing in a COP system is done one coil at a time. The diagnostic process, based on analyzing the waveform’s results, remains the same, however, regardless of the system. There are several alternative methods available to test these systems.

The first method uses a specific coil adapter based on application, as previously shown. Secondary patterns from COP systems are sometimes difficult to obtain due to the coil’s location, insulating qualities, and transistor placement. These adapters are available from tool vendors or the scope manufacturer—e.g., Snap-on offers many. Application-specific adapters have a unique shape based on the coil’s construction. Each adapter mounts to the coil differently, to enhance secondary signal collection and output to the scope. Therefore, when using these adapters, follow the manufacturer’s installation recommendations.

Another technique involves a universal wand probe or adapter that is placed on top or on the side of the COP. These wands are available from several tool truck vendors; alternatively, do a quick Internet search for retail tool suppliers to find one. Universal wand-type adapters can be used on any secondary ignition system.

If access to the COPs is not an issue, use HT leads. Remove the coil(s) and connect HT leads, or long spark plug wires, between the coil and spark plug. Attach a capacitive clamp around the plug wire or extension lead to view the waveform. Ensure the lead is securely connected to the COP and spark plug; an extra gap due to a poor location will appear as resistance on the waveform in the firing kV and spark duration.

In a two-wire coil application coil, direct primary access is available. Back probe the ground (switching) wire, and substitute the primary waveform for the secondary (FIGURE 16-32). Remember that the primary and secondary patterns mirror each other, so a fault in the system will appear in either.

FIGURE 16-32 Secondary ignition COP waveform using an inductive pickup. The resolution of the signal will vary from vehicle to vehicle, based on coil construction and probe location on the coil. In a COP system, secondary waveforms are checked at each coil individually. Always attempt to place the probe in the same position with the same pressure on each coil, for comparative analysis. Placement and pressure of the probe or paddle will affect the signal displayed on the scope.