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  #1  
Old 11-04-2002, 02:09 PM
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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
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  #2  
Old 11-04-2002, 04:13 PM
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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.
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  #3  
Old 11-04-2002, 04:58 PM
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Dave,
Thanks for the response.
J.Chip
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  #4  
Old 11-04-2002, 05:06 PM
LarryBible
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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,
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  #5  
Old 11-04-2002, 05:26 PM
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I'm using a Fluke digital multimeter with an auto scaling feature. Very high quality instrument so I'm sure its correct.
Thanks.
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  #6  
Old 11-06-2002, 10:05 PM
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Problem solved

Sure enough, it was the coil. Replaced it and all is fine.
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  #7  
Old 11-07-2002, 09:37 AM
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Electrons can do anything
 
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Cool!
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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