Tips for Effective Secondary Ignition Analysis

APPLICATION NOTES

The 6300/6310 portable reciprocating machine analyzer has two modes for analyzing secondary ignition system performance. The first method is the ionization voltage vs. crank angle. This analysis produces a report and gives statistics for multiple cycles of data. The user can view the mean of the ionization voltage along with complete statistics (high, low, spread, standard deviation, mean angular location, high angle, low angle, angular spread, and angular standard deviation). The second analysis method is the secondary detail trace. This analysis shows a detail trace of the secondary event giving the analyst the ability to view ionization voltage, arc duration, and coil ringdown. No report is generated for this analysis.

For both of these analysis, the secondary ignition capacitive pickup is used. Best analysis results are obtained when some simple techniques are used regarding the capacitive pickup. Firstly, the pickup has a ground clip. This clip should be connected before the capacitive pickup, and should be connected to a point that is solidly connected to the ignition system ground. Usually, the engine head is a good point, but the analyst needs to verify that the head of the engine is solidly connected to the ignition system ground. Also, be sure that a metallic contact is obtained - avoid painted or oxidized surfaces. Next attach the capacitive clip to the ignition secondary wiring. The best place to position the clip is in the middle of the wire from the coil tower to the spark plug or plug extension. If the clip slips down to the plug or coil tower, misleading readings can be obtained because of direct arcing to the capacitive clip. To avoid the slippage, a small piece of foam can be applied to the inside of the capacitive clip so that when the clip closes around the secondary wire, it will not slip. Another tip is to keep the secondary wire and clip away from grounded surfaces. If the clip or secondary wire is allowed to come in close proximity to the engine head, confusing data can result.

Consistency is the key. Clip placement and grounding should be consistent for all ignition secondaries on the machine. When these simple rules are observed, the data is more reliable and provides better troubleshooting information.

Secondary polarity:

There is some confusion to secondary voltage polarity. All ignition system manufacturers and plug manufacturers will say that the plug should fire with a negative ionization voltage. Negative firing plugs will fire with a lower voltage and the plug life is extended. The reason for this is that with a negatively firing system, the electrons travel from the plug's center electrode to the side electrode. The center electrode is designed to retain heat, so that when the plug is ready to fire, the electrical emissivity of the center electrode is higher than the side electrode. In other words, it is easier for electrons to be emitted from hotter surface. The 6300/6310 can be set up to analyze both positive and negative going secondaries. If the 6300/6310 is set up to analyze negative going, and the secondary is actually positive going, the analyzer will trigger on ringdown rather than the actual ionization voltage. The resultant data not be representative of the ionization voltage. To verify your system's polarity, use the detail trace mode to get an actual trace. In a negative system the voltage will appear as below. A positive system's trace will be inverted.