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Discussion Starter #1
Probably a newbie question and I did a search on the forum and couldn't find an answer. Working on a 2006 Ultra Classic flhtcui that had rough idle, missing and backfiring on the high end. Would also die at idle sometimes. Planning to replace fuel filter, fuel lines, spark plugs, plug wires and intake seal (and new Map sensor). Bike has 62k miles and I figured while I was in there I would replace all i could within a budget. While tearing down I considered replace the coil as well but was trying to test to see if it was faulty. Service Manual indicated secondary resistance @ 2500 to 3500 ohms. I'm testing from one terminal to the other as in attached pic and getting a reading of 6.3 ohms at setting of 20k. Again I'm a newbie but I think this is 6300 ohms which would be out of range for spec OR am I doing this all wrong.

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I am not sure but every coil I have ever measured was reading from the coil to common, not across the two outputs as your picture indicates.
 

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Discussion Starter #3
Thanks 01Ron. I "believe" I can test secondary resistance with the coil "off bike" based on some research and video I've viewed. Not sure how accurate it was that's how they did it . I did find more that adds more confusion. My service manual for my 2006 FLHTCUI has two sections listed for resistance specs. I attached two pics from the manual to show. The first pic is from the service manual and is for a carb'ed ultra (5500-7500 ohms) and my resistance (6.30 or 6300) falls inline with that spec. However, the second pic is for an EFI model and specs says (2500 to 3500) which I'm out of spec. My Ultra is in fact an EFI so not sure if i'm having a coil issue or if I'm OK. I hate to drop $105 for a new one if its Ok. Thanks!

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Once again, I believe you should be reading each secondary (sparkplug connection) to whatever is the common feed to both coils. Reading between both secondary output (sparkplug connection) would probably give you double the resistance. And if that's correct, double the spec would be 5000 to 7000 and your coil is probably good. But if you don't read from the secondary outputs (sparkplug connection) to what ever is the return side on each side of the coils, you are not reading the actual secondary resistance of each circuit in the coil. A dual coil contains two primary windings and two secondary windings. If I'm out in left field, I'm sorry since I have never checked a Harley EFI coil but I've check many other types of coils in the past. Maybe I should not even be commenting without an electrical diagnostics manual for your bike. And looking into this a little further, I believe you have to read the secondary resistance by reading between each sparkplug output to the common 12v connection on the coil. Here's what I found for a 2007 sportster coil.
sportster coil.jpg
 

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check the primary resistance as well,,, from 12v in terminal to trigger terminal of each side of the coil 0.5 ohms + or - 0.2 ohms..to7chthe center terminal with 1 probe then touch either one of the terminals on either side of the terminal you are already connected to,,, then touch the other terminal,,, thats all there is to it..
 

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Terry, I was going to recommend the same thing but you beat me to it! I was so focused on the secondary but the image I posted is almost self explanatory including the primary resistance.
 

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Discussion Starter #7
Thanks guys. I'll put back on the bike and test from there following your directions. Appreciate it.
 

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ive seen quite a few coils that ran well when cool,,, after a ride,, 20 miles or so, the engins would have erratic misses,, when shut off would not restart until they cooled off..

you can use a hair dryer or heat gun to warm the coil up,,, while you have already connected the leads,, you can now watch the resistant changes as they occur...anything over a half ohm,, is a problem.. ive seen the resistance come close to doubling

doing the test on the bike sucks,, you must disconnect the primary leads for the test to be accurate,, as the coil is coling down..
 
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