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This is a good waveform |
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Aston Martin V8 |
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Triple Spark Waveform Notes
The triple spark replaces the usual single shot spark found on most systems. The idea is to use 3 sparks in quick succession to improve combustion by lowering the idle and decreasing low rpm emissions. The triple spark is replaced by the usual single spark once a preset rpm is reached – usually in the region of 2500 rpm. Triple spark is used mainly on large CID V8 engines.
This waveform was captured on a big V8 engine at idle, using coil-on-plug configuration (8 separate coils). Each coil is individually controlled by the PCM. The waveform was captured using a 2-channel PicoScope automotive oscilloscope in conjunction with our coil-on-plug ignition HT probe.
So what can we see in the waveform? Well, notice that the first 2 sparks are of a shorter than usual duration – the pcm re-energises the coil after less than 1 ms of burn time, to top-up the charge in the coil, then switches off the current again to produce another spark at the plug. On the last spark, the full stored energy in the coil is used, finishing up with the usual coil oscillations caused by the last drop of energy left in the coil when the spark dies ringing away into the coil’s internal impedance.
Testing the system is done coil-by-coil, using the coil-on-plug probe. The general form of the pattern is checked in the usual way, but lift the engine rpm and confirm that the system switches over to single spark at the same rpm at each coil, and that the pattern is stable and consistent through the rpm range of the motor with no misfiring.
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