Not only was my RX8 coil discolored on the bottom.

  IT WAS DEAD!!!!!!!!!!!!!!!!!!!!!!!!!

  I could have lost the engine any minute.
  No indication what so ever that it was dead.
  No noticeable loss of power. Of course that
  was the trailing (top) plug.

  If the check engine light had come on I would have known
  about it but it did not!!!!!

  Minutes away from a new engine!!!!!!!!!!!!!!!!!

  Check those coils folks. I'll do it for you including
  shipping for $20 cash. All four. For a limited time
  only. Better yet get four new ones.
  Mine should be in in a day or so.

  Paul Lamar

 Paul...a Mazda service bulletin says that the discoloration on
 the bottom of the coils is normal and is not an indication of
 anything going bad.  One of the Mazda forums agrees with some of
 the messages saying that they have as much as 130,000 miles on
 discolored coils and testing showing no problems.  However, as
 you said, testing should be done after about 25,000 miles. Mazda
 suggests just a resistance test...attached is a copy of their
 service bulletin.

 Harley

 Thanks Harley for adding to the info on this.
 So far I have no less than 8 RX8 coils. I know my tester is
 working
 as some spark and some don't and I was very very careful about
 getting
 the drive to the coil right. The good old 50 cent CD 4050 does
 a masterful
 job of driving any transistor or FET. I have one coil that is
 bad with
 no discoloration.

 I will have a total of 12 shortly with the new ones coming from
 Pep Boys. Those too will be tested.

 In addition I can open and close the spark gap to measure the
 output voltage.

 I also have two running RX8 engines I can test them on.

 I have also noticed one other thing about them. They draw
 a huge amount of current during the 2 ms dwell time so make
 sure the ground and 12 volt wire is short and of high gage (18).

 I see from the Mazda service bulletin the trailing coil
 does not work during cranking. I wonder if Tracy implemented
 this feature? I also wonder why Mazda did that?

 Here is a simplified schematic of Tracy's EC2 to make it
 a bit easier to understand.

 I'll do one shortly for the RX8 coils.

 Paul Lamar

Paul...

Just pulled all four of my coils, and all of them are
discolored...the worst of the four (the 2nd trailing
plug...rearmost coil on the bracket) is shown below.  However,
using Mazda's service bulletin's resistance check method, only
the two trailing ones are bad (both terminals b to c and c to a
are open, so the wiring to c must be the culprit...a to b is ok).
The two leading coils check OK.

I've had no indication that any of them were bad (except maybe
the burned out O2 sensor?) as it's been starting and running very
well (even in the record breaking, consistently below freezing
weather and snow we had last month).  The strangest thing is that
the last half dozen or so tanks of gas have been giving me 22-24
mpg! My average (and I keep a spread sheet of every tank of gas
I've used since I got the car in 2003) was around 18-19 mpg.
Lowest tank full was 16.7. That was when I found the chipmunk
nest in my air filter box.

Replacing all the coils anyway.  Most of the parts dealers online
and locally want around $46 each...or more!  Pep boys locally
wanted $37, but even though Advanced Auto didn't stock them,
they're getting them for me for $25...the same brand (BWD) that
all of the others are selling.  If anyone's interested, Google
"BWD E1001" to get dealers and prices.

They'll be at the store near my son's house tomorrow about 9
AM...so I might be able to get a free meal off my son if I wait
until dinner time to drive up there to get them!

Time for a beer...

Harley