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