Ignition coil question
 

While troubleshooting an intermitent miss under accelerating conditions, I found the secondary of the ignition coil on my 1991 420 SEL to be "open", that is, infinity between terminals 1 & 4. Yet I get spark and the car runs fine except for the persistant miss under load conditions. Could the coil actually be "open" yet provide enough energy to jump the open gap and provide spark to the plugs?

J.Chip

Yep. Its possible that a small break in the wire will allow the coil to deliver a spark. There will be a small spark inside the coil where the break is located. If it is inside the coil, the spark will begin to carbonize the area around the spark area and that will lead to eventual failure of the coil.

Dave,
Thanks for the response.
J.Chip

The explanation is correct, but I just want to make sure you are not measuring with the lowest scale on your ohmmeter. Go to a X1K or X100 and try it again. The X1 scale on some meters may lead you to believe that it is open when it is not.

Good luck,

I'm using a Fluke digital multimeter with an auto scaling feature. Very high quality instrument so I'm sure its correct.
Thanks.

Problem solved
 

Sure enough, it was the coil. Replaced it and all is fine.

Cool!