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The primary coils are probably not breaking down. The secondary coils have very high voltage. The voltage in the secondary coil depends on two variables related to the spark plug. The voltage is mosty controlled by the spark plug gap. This "break down" voltage is mosty proportional to the spark plug gap. So if the gap is 10% wider, the voltage will go up by 10%. And while this is happening, the breakdown voltage for a given air gap increases with the pressure in the combustion chamber. So for the same plug, the breakdown voltage increases with boost pressure and drops with manifold vacuum. One can expect that variations in breakdown voltage via spark plug gap will be in the +/- 10% order of magnitude. This is quite small. If a solid center electrode is replaced with a fine platinum wire in ceramic, this creates a voltage stress concentration which will reduce the breakdowm voltages. I ran VX platinums for years in my 95SET, and will transfer these old plugs to my 95 Aero when the time comes.
So what happens if you have a very large gap? I once made an electic fence unit with a HP coil and capicotor discharge ignition systen. That thing could throw a 1.5" spark! It would always jump a fence insulator somewhere on the property and you could hear the snapping when walking the fence lines. I put some old 4 ft floresent tubes near the fence and they would all pulse. My friend came by after I did this and he had helped my set up the fence originally. He heard the snapping and walked over to the gate to the snapping insulator. It was sunny, but he was determined to try to see where the spark was. There was a wire sticking out from where the fencer wire was twisted, and he looked closer and closer and a spark jumped out and hit him in thne forehead. He aways was a strange kind of fellow, so it was hard to attribute his later problems to the fencer! And yes, the end of the story is that a coil with this large spark gap situation will lead to the secondary coil breaking down internally.
The DI is quite complex and electronics and capacitors running with heat and vibration will simply fail in a predicable fashion. So get over it. it is part of the best engine control system every made, but it is not eternal. Tires and brakes wear out too.
The way that DIs fail with the smell of burning epoxy suggests that a semiconductor has burned, which often means that it goes completely conductive. So that failure means the DI does not work anymore. If the power is left on, things start to cook. A good design would try to deal with such a failure by including power resistors that act as current limits, but overheating still results. Red high milage younger DI's tend to fail sudden death in hotter weather. Red DI's that are older with moderate miles have a pattern of starting problems and running problems, but not so much the sudden death no warning problem, which seems to happen moreso in any season. I don't know how the black DIs die off.
NG900 and 9-3 red DI owners have be advised to replace older still funtioning DI's with a new one, and keep the old one as a spare. And if they have a running problem that might be a DI, get a new one and if that does not fix the problem, then they have the spare that they need anyways. That works well for the DI's that create problems without failing completely. http://www.Europarts.com has the best prices it seems, no tax and free shipping.
posted by 65.68.1...
, Fri, 29 Nov 2002 18:49:16, Sat, 30 Nov 2002 15:38:38
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