Chapter 34 Advanced Diagnostics 677 Copyright by Goodheart-Willcox Co., Inc. Ignition Scope Test Patterns Th ere are four scope test patterns sometimes used by the technician when diagnosing diffi cult to fi nd ignition problems: primary superimposed, secondary superimposed, parade (display), and raster (stacked). Primary Superimposed Pattern Th e primary superimposed pattern shows the low volt- ages in the primary system for all cylinders stacked together. Superimposed means that the patterns for all the cylinders are placed on top of one another. If one pattern does not align, that cylinder has a problem. See Figure 34-34A. Secondary Superimposed Pattern Th e secondary superimposed pattern places all the cylinder high-voltage waveforms on top of each other. Th e superimposed secondary waveform allows you to quickly check the operating condition of all cylinders. For example, if one spark plug is not fi ring properly, the waveform for that cylinder (spark plug) will not align with the others. Th e abnormal trace will stand out because the fi ring voltage is higher or lower than normal. Th e secondary superimposed pattern is used to check for general problems in the ignition system. If one of the wave- forms is out of place, the other scope patterns may be used to fi nd exactly which component is causing the problem. Parade Pattern Th e parade pattern, also called the display pattern, lines up the waveform for each cylinder side by side across the screen. Th e other cylinders are displayed in fi ring order, Figure 34-34B. Th is makes the parade pattern useful for comparing fi ring volt- ages of each spark plug. If one or more fi ring lines are too tall or short, a problem is present in those cylinders. During normal operating conditions, secondary volt- ages will usually vary 7 kV to 25 kV for electronic ignitions. A tall fi ring line on the parade pattern indicates high resistance in the ignition secondary caused by an open spark plug wire, a wide spark plug gap, a burned coil pack connec- tion, or a burned secondary connection in a distributorless ignition. High resistance requires higher voltage output from the ignition coil. A short fi ring line indicates low resistance in the igni- tion secondary, which may be an indication of leaking coil pack, spark plug wire insulation, oil-fouled spark plugs, carbon tracking, or similar problems. Not as much voltage would be needed because of a short to ground. Raster Pattern In a raster pattern, or stacked pattern, the voltage waveforms are placed one above the other, Figure 34-34C. Th e raster pattern is normally used to check timing or dwell variations between cylinders caused by camshaft or crank- shaft sensor problems, bad PCM, etc. Figure 34-34. Three common scope test patterns. A—Super- imposed. B—Parade pattern. C—Stacked, or raster, pattern. (FMC) 0 5 10 20 10 0 30 15 0 5 10 20 10 0 30 15 0 5 10 20 10 0 30 15 A—Superimposed display has all patterns on top of each other. It checks that all patterns are uniform. B—Parade display has cylinder patterns side by side in firing order. It is useful for comparing firing voltages. Number one cylinder is on left, with its firing line on the right. C—Stacked or raster has all cylinders one above the other. It is useful for comparing duration of events. Number one is on bottom. Others are in firing order. Ignition Coil Output Test A scope ignition coil output test measures the maxi- mum available voltage produced by the ignition coil. A spark plug only requires about 5 kV to 20 kV for operation. However, the ignition coil should have a higher reserve voltage. Without this extra voltage, the spark plugs could misfi re under load or at high engine speeds when voltage requirements are greater. To perform the coil output test, set the scope controls to display the highest kV range. Run the engine at 1000 to