Ignition Coils
  Links
    Understanding Ignition Coils
      http://www.forparts.com/ICignitioncoil01.03.htm
    Multi-Coil Ignition Systems
      http://www.aa1car.com/library/2004/us20406.htm 
  Symptoms of Bad Coils
    Cranking, no-spark condition
    Severe backfire
    Temperature or humidity-related starting or stalling problems
    Weak spark
    Hard starting
    Hesitation or misfire under load or when accelerating (this was mine)
  Failure Modes - springer3
    Electro-mechanical forces cause micro-movements in the windings
    Coil wire can break (total failure)
    Short out individual turns of coil (lower output)
    Short from primary to secondary winding (internal arcing; xmas tree)
  Testing
    pull each igniter connection, one at a time, and try to start engine
      engine shld run (fine) on either coil
    test spark
      shld be a nice blue spark.
      if any other color (red, orange, yellow) then coil bad (low output)
        blue - ionized oxygen
        red  - ionized nitrogen 
    how to test (http://www.forparts.com/ICignitioncoil01.03.htm)
      a) open-circuit spark output
         a good coil produces a bright blue spark that jumps a 1/4-inch gap
         on a spark tester
      b) passive resistance in the primary and secondary coil circuits
         although the resistance test is not a definitive measure of a
         coil's electrical integrity, a coil should be replaced if the
         resistance values don't fall within specifications
      c) current rise or "ramp" through the primary windings
         using a low-amperage current probe to measure the current "ramp"
         through the primary ignition circuit is perhaps the most
         definitive method of determining the electrical integrity of the
         coil and the quality of the triggering action
      why coils fail
         Because worn spark plugs and open-circuit spark plug wires force
         ignition coils to operate at maximum output, neglected ignition
         system maintenance is the most common cause of modern ignition
         coil failure. As the spark plug air gap widens due to normal
         erosion, increased voltage is required to create a spark in the
         combustion chamber. This increased voltage, in turn, demands more
         current flow through the coil's primary circuit. And, this
         increased primary current flow can overload the ICM's primary
         transistor. The increased secondary current created by the
         ignition coil also can increase to the point that it perforates
         the secondary circuit in the coil itself.
  Warning
    An important point to keep in mind with respect to all types of
    ignition coils is that when the magnetic field collapses, the
    high-voltage surge has to go someplace. If it can't go to the spark
    plug, it will find another path to ground - which may be back through
    the ignition module, PCM driver circuit or through the insulation
    inside the coil itself. This can be very damaging to these parts. So
    never disconnect a plug wire or COP coil while the engine is
    running. It can be very damaging as well as dangerous to you should you
    become the path to ground.