Question about testing coils

[GLoweVA]

I looked it over and it seemed okay. I checked the fork place.

If it were the return, I shouldn't be able to measure ~12v at the orange / grey when the key is on, right? Or are you saying to do a loop test from the front red/white to the back red/white at the TCI? If that were bad, wouldn't both coils not work?

Yeah, i guess I'm getting a little ahead of myself.
Okay, let me slow down a second.
Here's the diagram of the ignition circuit:


SO, you're getting 12V at the grey and orange wires and the coils ohm out good, so they've got to be good.?!?
But, you swapped the grey and orange and the no spark DIDN"T move to the other plugs!?!

Now I think I'm just as confused as you are now.

[fredintoon]

I was pulling the plugs out, grounding them and looking for a spark, not trying to actually start it. It should have sparked, unless I am just missing something here...

Hi VC,
you swapped the orange and grey wires. What that did was make the leftside coil think it was the rightside coil. What you were testing was still the leftside coil being sparked by the grey wire instead of the orange wire.
If you did the same test on the rightside coil and got no spark with the orange wire it's the orange wire ignition sender giving the trouble.

[TopCatGr58]

Wait a minute Fred.

He has fire on 1 coil, plugs 2-3 but none on 2nd coil plugs 1-4. He then swapped the orange /gray trigger wires for the 2 coils, and retested. He still had fire on the same coil/plugs, and not on the suspect coil. The alternate PU coil and trigger wire and TCI were triggering opposite coils than before, but the problem didn't move...it stayed with the same coil/plugs, so that shows that the TCI and PU coils and trigger wires were still working because the same coil had fire, and the suspect coil did not. So this shows that the ignition coil is suspect.

May I remind folks that he's talking about the Mikes XS Green coils. We know that both their cheaper black ones as well as the green ones are of inferior construction. The black ones burn out after about 10k miles, the green ones are a little stronger, but a few folks have reported failure with them as well. MikesXS states that they are NOT to be tested without spark plugs connected and properly grounded to ensure a complete circuit! Laying the plug on the head doesn't necessarily ensure a good contact with the head for testing. They also do NOT WARRANTEE their coils...another RED FLAG with regards to their suspect quality. Whereas Dyna-Tek provides a year warrantee.

Warning: Serious High VoltageClick here to see Coil Test DataWARNING!!! Do not operate or apply power to the ignition system with one or both spark plugs disconnected. Operating or applying power to the coil or ignition system with one or both spark plugs disconnected will cause IMMEDIATE FAILURE to the coil. Ignition coils are not warrantied for this reason.

When my MikesXS Black coils failed, they still ohmed out at the proper values yet surprisingly they....1 burned up just a few miles from home after 200+ mile long trip! I installed the Dyna-Tek coils and problem solved...hit on all 4 again immediately!

T.C.

[vcgodinich]

Yeah, i guess I'm getting a little ahead of myself.
Okay, let me slow down a second.
Here's the diagram of the ignition circuit:

SO, you're getting 12V at the grey and orange wires and the coils ohm out good, so they've got to be good.?!?
But, you swapped the grey and orange and the no spark DIDN"T move to the other plugs!?!

Now I think I'm just as confused as you are now.

Yes. And the known good wires didn't cause a spark on the suspect coil.

All signs point to a bad coil, except that it ohms out good, primary, secondary and no cross over between the two.

[vcgodinich]

Wait a minute Fred.

He has fire on 1 coil, plugs 2-3 but none on 2nd coil plugs 1-4. He then swapped the orange /gray trigger wires for the 2 coils, and retested. He still had fire on the same coil/plugs, and not on the suspect coil. The alternate PU coil and trigger wire and TCI were triggering opposite coils than before, but the problem didn't move...it stayed with the same coil/plugs, so that shows that the TCI and PU coils and trigger wires were still working because the same coil had fire, and the suspect coil did not. So this shows that the ignition coil is suspect.

May I remind folks that he's talking about the Mikes XS Green coils. We know that both their cheaper black ones as well as the green ones are of inferior construction. The black ones burn out after about 10k miles, the green ones are a little stronger, but a few folks have reported failure with them as well. MikesXS states that they are NOT to be tested without spark plugs connected and properly grounded to ensure a complete circuit! Laying the plug on the head doesn't necessarily ensure a good contact with the head for testing. They also do NOT WARRANTEE their coils...another RED FLAG with regards to their suspect quality. Whereas Dyna-Tek provides a year warrantee.



When my MikesXS Black coils failed, they still ohmed out at the proper values yet surprisingly they....1 burned up just a few miles from home after 200+ mile long trip! I installed the Dyna-Tek coils and problem solved...hit on all 4 again immediately!

T.C.

Kinda what I am thinking. I have been careful not to crank without out everything grounded, but maybe grounding to the case isn't good enough?

I suspect the coil is bad, even though it tests okay, just wanted to see if this was a thing that could happen (test okay, but coil still bad)

[CaptonZap]

Here's a hypothetical.
The insulation between the high tension coil and the primary coil developed a leak at one spot. The resistance of the two coils didn't change, but when the field collapsed, the high voltage current found it easier to jump from the high tension coil to the low tension coil, (which is now grounded through the TCI,) and thus to ground. A case of internal arcing.
It would be interesting to put a O-scope on the black wire coming out of the TCI and see what sort of wave form was developed when the coil was supposed to fire. Or compare the readings of an analog volt meter between the good and bad coil, trying each with the other disconnected from the r/w feed wire.

Just some musing. CZ

[vcgodinich]

Here's a hypothetical.
The insulation between the high tension coil and the primary coil developed a leak at one spot. The resistance of the two coils didn't change, but when the field collapsed, the high voltage current found it easier to jump from the high tension coil to the low tension coil, (which is now grounded through the TCI,) and thus to ground. A case of internal arcing.
It would be interesting to put a O-scope on the black wire coming out of the TCI and see what sort of wave form was developed when the coil was supposed to fire. Or compare the readings of an analog volt meter between the good and bad coil, trying each with the other disconnected from the r/w feed wire.

Just some musing. CZ

would this mess up the TCI / blow a fuse?

Going to put back on the old coils and test them out.

[fredintoon]

Wait a minute Fred.

He has fire on 1 coil, plugs 2-3 but none on 2nd coil plugs 1-4. He then swapped the orange /gray trigger wires for the 2 coils, and retested. He still had fire on the same coil/plugs, and not on the suspect coil. The alternate PU coil and trigger wire and TCI were triggering opposite coils than before, but the problem didn't move...it stayed with the same coil/plugs, so that shows that the TCI and PU coils and trigger wires were still working because the same coil had fire, and the suspect coil did not. So this shows that the ignition coil is suspect.
- - -

Hi TC,
on second thought, yeah, you are right. I must be losin' it.
For sure MikesXS coils don't have a good rep.
If the bike runs good when the old coils are re-installed, it's proof enough that the replacements were a bad bargain.

[CaptonZap]

would this mess up the TCI / blow a fuse?

Going to put back on the old coils and test them out.

The path to ground through the TCI goes through the big transistor on the board, and since the power in the spark is no more than the power put into the coil, I'm guessing that the transistor would not be affected as long as all the power was dissipated before the transistor opened up again. Crazy Steve might be a better source of definitive info on that score. The voltage of the leakage would depend on the location of the insulation breakdown inside the coils.
There are no fuses in the TCI, and as long as the ignition fuse doesn't blow, you should not have any over current problems.
One test that I always thought was good was to see if the coil would jump a 3/16 inch gap in ambient air. The stress put on the insulation with that gap is not great enough to hurt the insulation, and if it will put out that size spark in atmospheric pressure, it will probably fire at 150 psi in the chamber.
Most old magnetos had an internal spark gap set at 1/4 inch to prevent the coil insulation from being harmed if the plug wire came off of the plug, and the high tension current had no place to go.
We don't have that safety in our systems, so if you are riding along, and a plug cap falls off, you stand a good chance of hurting the coil.
Let us know what you find out with the old coils versus the new.

CZ

[crazy steve]

The path to ground through the TCI goes through the big transistor on the board, and since the power in the spark is no more than the power put into the coil, I'm guessing that the transistor would not be affected as long as all the power was dissipated before the transistor opened up again. Crazy Steve might be a better source of definitive info on that score. The voltage of the leakage would depend on the location of the insulation breakdown inside the coils.

That could really depend on where the internal short is. CZ is correct in that the 'power out' can't be greater than the 'power in', but voltage can certainly be different. IIRC, solid-state devices don't like high transient voltages as that can damage the junction at the semiconductor.

Something like this will be impossible to diagnose with a simple meter; you'll really need a o-scope on the live circuit to 'see' what's happening.

I'll also point out that 14K ohms cap-to-cap is not the correct spec if you have 5K ohm plug caps installed. That would put the secondary at under 5K ohms, which would result in weak/no spark; basically reducing your output by 2/3. Check the secondary resistance at the coil (without wires); you should see about 15K ohms, if it's substantially lower you have a bad coil.