Miata Mailing List: November 1998, Message #663

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Thanks for the various suggestions. I've replied to all by
email, but here is an update on my misfiring ignition coils.

Most folks suggest that it's electrical noise that's causing
multiple firing of the coils. Bill C at dlralt encountered a
similar problem when he was doing some early ECU work. I also
heard MCA/Norm talked about something similar two issues ago.
I'll have to look it up.

I pulled the coils out and bench tested them. Spark. Crackle.
The ones from my car fire around 1.25 volts. I assume that this
is typical  and that my coils aren't degraded. There's as 
much as a volt jumping around in the background when the coils
misfire, so it's easy to see how that happens,

So the good news is that I probably don't have to spend $250
at Mazda for a new coil. The bad news is that I now need to look
for the source of noise. I hope it's just a bad ground connection....


Harry Sue
Chicgao