If you truly have spark at the coil but not at the plug about the only thing that can happen is the rotor has a hole burnt through it. It will appear as a dark spot. That or moisture inside your cap or a shorted coil to dist wire with the spark jumping out of the wire.
[This message has been edited by phonedawgz (edited 12-13-2013).]
When dealing with high voltage an ohm meter is only somewhat helpful. The ohm meter measures the resistance at a very low voltage. The spark operates at a high voltage. So lets say there is a micro-hole in the rotor. Because there is an air gap between the metal of the rotor and the dist shaft the ohm meter will read infinite ohms. But the spark will still jump to ground there.
When the ICM fires the coil the voltage in the coil will build until it finds a place where it can jump to ground. If you check for spark by holding the wire away from the block the voltage will increase the farther the wire is from the block. So perhaps your testing procedure is changing as you change from the coil to the spark plug. Note also - a spark plug installed in a cylinder will need even much higher voltage to fire. So if you are testing by using a timing light and you are't getting a spark with the wire connected to the plug but you can get a spark outside the cylinder that is because inside the compressed cylinder more voltage is needed. So bad insulation in the coil can give you an situation where you can get spark outside the cylinder but when connected to a plug, the higher voltage needed is above the defect in the coil and you no longer get a spark.
... inside the compressed cylinder more voltage is needed. So bad insulation in the coil can give you an situation where you can get spark outside the cylinder but when connected to a plug, the higher voltage needed is above the defect in the coil and you no longer get a spark.
I was taught a long time ago that the spark needed to be strong enough to jump a 1/4" gap outside the cylinder.
yeah, pretty much. I pulled the related connectors and re-seated them. and all of a sudden I had signal to the injector bank that wasn't getting any. everything checked out fine after that, so I checked the last thing after the electrical issue was solved, which was the plugs. changed them all out at the proper gap and then she fired right up, timing was off so I re-set that, and now she's nice and healthy.