Ignition Coil Question

I have a coil where the I can measure the resistance on the primary side. It is 3.9 Ohm - perhaps a little high.

On the secondary side, I can not get a reading at all. Two different DMMs, no difference.

Bike seems to be running fine. Is it possible that this coil is bad enough that resistance can't be measured but the bike still runs??

 

Something is wrong with your testing technique if the multimeter isn't reading, I'm thinking.
Maybe the plugcaps are too deep for your probes?
But in saying that, take the plugcaps off and stick the probes in the actual cable holes, to get a reading.
Or... if the bike is running fine... leave it be!

 

Or, just like the high voltage will jump the gap on the spark plug, the open in the secondary winding or plug wire is such that the high voltage will exceed the gap and spark the plug, but a low voltage DMM will see this as an open. If you are sure you are getting good contact and performing the procedure correctly (DMM set properly) then you should replace the coil as the internal open will likely grow in size and eventually completely fail.

 

Rooster you are the man, no matter what electronic wise but the question still remains...
Why are we testing coils on a bike that runs fine?

I agree, better testing equipment is better and I love better equipment. Lets see what Dan comes up with.
We are here to help and/or be educated.

 

Thanks guys.

I suppose it makes sense that there could be a break in the secondary and that it could jump just like a spark plug. Therefore, it would still work and the plugs still fire, but would not be able to be measured.

I have two DMMs. Neither is expensive, so I don't have high expectations from them. One is auto-ranging and one is the type where you have to set the Ohm range manually. Of course my procedure is suspect - I'm no expert in these things. I measured with the caps off. All the caps measured fine by themselves (~5K Ohm). If I can't get a reading on either of the DMMs that's when I get suspicious and post a question like the original question.

Why would I be testing a bike that runs fine? That's a fair question. I had the DMMs out to test the ignition components of another bike that was not running so nicely. I found some interesting surprises on the other bike, so I decided that while I was at it I would test the components on this bike. I have also learned that you can't make any assumptions about the condition of anything on these things.

I guess the "safe" thing to do is to put a new set of coil packs on my list of things to do. Fortunately, they are not super expensive, so it may be cheap insurance against a "bad day".

 

I agree with rooster53, think of your spark plug gap, the larger the gap the larger the electrical charge must be to jump the that gap.

 

Hello dan.
I have the same problem.
Identical readings in primary and zero resistance in secondary.
Did you have to change the coil? Or is it still working? Thanks!!

 

Hi @Litaos. I have not changed the coil yet. I bought a box of parts that included a coil, so I have one to use. I will replace the coil when I get the bike out from winter storage.

It was still working when I put the bike into storage. I'm not sure how well it was working, but it was working.

Someday, I would like to replace the coils and plug wires with new versions, change the caps to non-resistor, and change the plugs to a resistor version.

 

buena informacion, me preocupa el alto valor de 3.6 ohmios en el primario.
En el proceso de restauración cambié la tapa de la bujía (Ngk Xdo5f) con 5 ohmios de resistencia + bujías ngk bp7es.
Todavía estoy inspeccionando el circuito eléctrico.
¡¡Muchas gracias!!

 

Yes, 3.6 Ohm is technically out of spec.

You should probably do what I did - put replacing the coils on the list of things to do someday when you have the time and money to do it.

 

where is the translate button?

 

https://translate.google.com/

Actually works pretty well.

As much as I'd like to say I'm multi-lingual, I am not. I sent my children to a language immersion school. They are still bitter about that. Someday they will appreciate it.

 

“Good information, I'm worried about the high value of 3.6 ohms in the primary.

In the restoration process I changed the spark plug lid (Ngk Xdo5f) with 5 ohms of resistance + spark plugs ngk bp7es.

I'm still inspecting the electrical circuit.

Thank you very much!!”

The translate function on the iPhone works pretty well.

 

Stupid question but are you both using the 'Clymer method' to test your coils? This is depicted incorrectly in their manuals and why I have a
spare set of coils from ebay
Secondarys are measured from HT to HT on a twin coil. IIRC.

 

Measuring from the end of one plug wire to the end of the other

 

What is the Cymler method?

 

It shows the meter probes measuring between primary and secondary..

 

I'm no electrical engineer, but as far as I know, that will definitely not work!

Thanks @a100man, hopefully that can prevent future readers from a severe case of "having a bad time".

To be honest, it took me a while to figure out how properly measure them. Once I did some research on how ignition coils work, it made sense. Is there a how-to somewhere around here that shows explicitly how to do these measurements? If not, somebody should do that - would probably help lots of people like me who scratched their heads for a while before figuring out how to do it.

 

Here is a pretty good general how-to:

 

This has been discussed in the past but if you don't search hard enough you would not find it. I already knew this from checking my XJ700 but when I got the XJ700X and was checking, I did it wrong and was scratching my head until I remembered the manual was wrong.

 

could be your meter is not set properly for what you are trying to measure.

rooster is correct on the spark jumping the gap in the wire.

so you can record the specs

I like to have a history on a bike and its systems..
I check every value and record it.

a bike can run fine but you still may have low charging voltage output. so if i know the spec and what i have for a reading I can put it on my list of work i may need to do to improve the charging system.
I have gotten a few bikes that run well but parts like sparkplug caps are out of spec. put those on the list to replace.

valve shim specs all good but if you have the specs and current sizes you will have an idea on which shims may need to be replaced in the future and what size you will want to have on hand when i do the first shim check in spec or not the shim is pulled and size recorded.

then I will pick up a few shims i may need. i like to keep the amount of times i remove the cover down to a minimum , open it check and change shims, is better than open it close it then open again to change shim,
all that time spent doing something over is down time from riding

just like i have extra oil and filters on hand at all times.

I would rather have an extra part or 2 on my shelf that have down time waiting for a part to come in