I have some general questions on coil on plug igniter modules (some call them amplifier modules, but as they seem to be a switching device I will call them igniter modules for the purposes of this discussion).
My questions are re failure modes and testing procedures. I will use for example the expensive, and now obsolete ignition igniters for the Nissan RB26-DETT twin turbo straight six Skyline engines. I and many others have experienced issues with these. Sometimes they will fail to fire on one, or sometimes more than one, coil. The coil is not triggered at all. The thing's kaput and needs changing. But I and may others have had several experiences where the module only fails to fire one or more coils when the engine is around peak torque and cylinders pressures should be around their highest. Idle, starting and off very much boost running, is unaffected. Take it up around peak torque and boost and one or more plugs are not fired, either at all, or adequately and a stutter or lost cylinder results. Leave the status quo exactly as is, and renew the igniter, and all is fine again, so presumably neither a plug nor coil issue. Often this is also temperature related and the issue only becomes apparent at all when the igniter gets hot.
Now what is the failure mode of the igniter in this scenario? Are they FET's or BJT's that trigger the coils? I dissected a couple and they are gel filled with the semiconductors are embedded in / on a small heatsink with fine gold wire leads to some surface mount components Can they see different switching currents dependent on cylinder pressure? IE, does each coil on plug see different current draw depending on the voltage needed to jump the gap? What is this interim failure mode likely to be at the component level?
As an aside, short wiring lengths apart, why the hell did Nissan think atop the head, in a very hot region, with a thermal path straight into the head casting, a good place to mount the damned things?
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I fixed my failure issues ages ago on my MOTEC M800 ecu'd M800 RB26-DETT engine with the two 3 cylinder Bosch igniters from a Volvo V90 straight six, mounted on an alloy heat sink, well away from engine heat and vibration, but would like to get a technical handle on why these (and I mean not just Nissan ones, other makes suffer similar issues) can falter when the plug is asked to fire high cylinder pressures, yet be OK for a while when the engine is not put under appreciable loads.
Has there ever been a commercial test rig for igniters that trigger them from say a signal generator, and load their outputs either electronically, or by actually firing coil packs with variable spark gaps whilst monitoring them with a `scope? Some of the things are very expensive and I don't like the "let's just replace it and hope it cured the miss" routine with expensive gizmos....
Thanks for reading!