Can coils fail intermittently?

[richardhaggarty]

I have been having a problem with my '85 GS700. Hard to start and no power. I thought fuel at first because I discovered my vacuum line was kinked under my tank. Problem went away then came back.

While it was running (poorly) I pulled off the number 4 wire; no change. So then I pulled off number 1 wire again, no change. Number 3, the engine died right away. So I feel confident I narrowed it down to a problem with one coil. I checked and tightened all the connections. Fixed.

Now its back again.

Can a coil go bad then good then bad again?

How do I do a pure test on the coil itself?

Thanks

[chiphead]

Because you are dealing with an electrical item ,yes it can fail intermittently, moreso as it gets hot.
Take a spare plug with you. Break off the curved electrode on the tip. When the failure occurs, put that plus in the cap, ground the side of the plug to the engine and check to see if the spark, if any jumps from the center electrode to the side of the plug. If not, you have an ignition problem. If it does, look elsewhere.

[richardhaggarty]

Thanks for the fast response Chip.

I used a spare spark plug to watch for spark while I was checking the coil connections rather than relying on starting the bike again.

Using the spare plug method I have confirmed more than once that sometimes there is no spark on wires 1 or 4. However, sometimes it fires right up and runs no problem.

Also, I should note that I have the Dyna 2000 ignition system and Dyna coils. I bought the coils used, there is a number stamped on the coils; 4/94. Assuming this means April 1994, is this an appropriate life span? How long should a coil last?

Thanks

[West]

No offense, chip, but I don't think your test is a good idea. On CDI ignitions, imposing a very high spark impedance can damage the system, that means either running with a plug completely disconnected or a very large air gap such as you have suggested. I would recommend using an unmodified plug with a standard gap & just look at the strength or existence of the spark.

Someone (chip) correct me if I'm wrong about this.

[chef1366]

See if your getting power to the coil with the key on. If you are it's probably the cdi unit not breaking the circit to create the jump across the spark pug.

[GSstiny]

You can test the primary and secondary windings of the coil with a DMM. The resistance on the primaries (the "in" wires) should be 3-5 ohms. The Secondaries (the "outs", plug wires) should show resistances readings somewhere between 21,000 and 25,000 ohms.

Im not exactly certain on the numbers for the secondaries, but thats a ballpark range. Ive seen Billy_Ricks post the test specs a couple times, hopefully he will chime in and confirm.

[Carter Turk]

I recently had a set of Dyna Coils 3ohm stamped 6/96 go bad. 1-4 was the culprit.

I also had a Dyna S installed recently, it failed too. One of the triggers (1-4) was faulty. They replaced it no charge.

As far as the coil goes they'll replace it for $35, but you have to send to them and they have to test it. It only took 8-9 days turnaround.

On mine they determined only one coil was bad and offered to sell a new one.

I opted for two at $70 and they sent the good one back as well.

While I waited for my new Dyna-S, I wired the old ignitor back in. It still in there today, haven't bothered to put the Dyna-S back in.

I've put a few thousand miles with new coils and old ignitor with no problems

[chiphead]

No offense, chip, but I don't think your test is a good idea. On CDI ignitions, imposing a very high spark impedance can damage the system, that means either running with a plug completely disconnected or a very large air gap such as you have suggested. I would recommend using an unmodified plug with a standard gap & just look at the strength or existence of the spark.

Someone (chip) correct me if I'm wrong about this.

Absolutely no offense taken West! The beauty of these forums is the open exchange of information and ideas. If someone thinks I'm talking out of my posterior they should say so and you did! No problemo.:-D
In the very far past Japanese manufactures provided dealers with devices that would measure the distance a spark would jump. 7mm seemed to be the limit if I remember correctly. McCullough actually provided a "special tool" that was exactly what I described. Granted they manufactured chain saws, but the ignitions were electronic and worked on the same principal. I think the original poster has a good handle on the problem so life is good. I myself will continue to use this test as necessary unless someone tells me it's a bad idea. You're points are valid, West, but I think that an electronic system should be able to handle a couple of cranks of high impedance.
My 2 cents.

[richardhaggarty]

I did some resistence tests with a meter.

Coil 1 and 4 is the suspected bad coil but, that dosen't seem to be reflected in these results. Any ideas?

Coil 1 and 4
Primary: 3.0 ohm
Secondary: 14,300 ohm

Coil 2 and 3
Primary: 3.0 ohm
Secondary: 14,130 ohm

chef suggested the cdi unit could be at fault. I have a Dyna 2000 ignition and am hoping that is not malfunctioning.

[Arkaloid]

Check connection TO the coil (B+), and make sure your getting 12 volts at it, and also check to see if wire is not chaffing somewhere casuing intermittent short, I dont think it is heat related, since you say it happens when cold also (during start, I presume cold start?). If you are NOT getting a full 12 volts at the coil, it can get real funky...

[richardhaggarty]

If you are NOT getting a full 12 volts at the coil, it can get real funky...

That is a good point Arkaloid. I noticed that the voltage at the coil is only reading about 11.5v. Same at the battery. Could simply a aging battery be the cause of the mysterious intermittent coil?

[BadBillyB]

Easy enough to swap the coils and see if the problem moves to the other 2 cylinders. Go to Dyna's website and download the troubleshooter section if you dont have the papers that came with it. You can put it in test mode and check a few things.....A simple "unpowered" test light will confirm whether the coils are being triggered. Connect one end to ground and the other to the negative side of the coil. When cranking the motor the light should blink if the coil is being triggered.....BadBillyB

[West]

Absolutely no offense taken West! The beauty of these forums is the open exchange of information and ideas. If someone thinks I'm talking out of my posterior they should say so and you did! No problemo.:-D
In the very far past Japanese manufactures provided dealers with devices that would measure the distance a spark would jump. 7mm seemed to be the limit if I remember correctly. McCullough actually provided a "special tool" that was exactly what I described. Granted they manufactured chain saws, but the ignitions were electronic and worked on the same principal. I think the original poster has a good handle on the problem so life is good. I myself will continue to use this test as necessary unless someone tells me it's a bad idea. You're points are valid, West, but I think that an electronic system should be able to handle a couple of cranks of high impedance.
My 2 cents.

That response was very openminded & gracious. Thanks. A chainsaw with a CDI Ignition? An old one? That's news to me. Where did they put the battery & alternator? Every chainsaw I have ever seen, old & new uses a magneto. An open circuit on a magneto won't hurt it a bit.

I know of the tester you are talking about, the spark jump distance is a way to measure the high tension voltage, but I doubt you will see something like that recommended by a CDI manufacturer.

I agree, a couple of cranks with a high impedance is statistically safe, as many people on this forum and elsewhere has pulled a wire off their plugs from time to time, CDI or old fashioned ignition notwithstanding. I think it is somewhat dangerous with a CDI, but not guaranteed fatal everytime. All I know is that every CDI manual I have ever read, (I'll have to go check out the Dyna site), they caution against running an open circuit. Why tempt fate?

As a quick note to another comment made earlier, a CDI ignition (dyna in this case) does not 'break' the circuit through the coils as an old point ignition does. It sends a relatively high frequency pulse through the low tension side to fire the coil & plug. I'm pretty sure it is the rise of the pulse that fires the plug, not the decay of voltage after current is interrupted as on an old fashioned ignition. Just for accuracy's sake.

[Billy Ricks]

You can test the primary and secondary windings of the coil with a DMM. The resistance on the primaries (the "in" wires) should be 3-5 ohms. The Secondaries (the "outs", plug wires) should show resistances readings somewhere between 21,000 and 25,000 ohms.

Im not exactly certain on the numbers for the secondaries, but thats a ballpark range. Ive seen Billy_Ricks post the test specs a couple times, hopefully he will chime in and confirm.

30k-50k is what you want to find on the secondary windings with stock coils. Probably about 30% less with Dynas and such.