Pull a plug wire to test ignition ???

[OldguyGlen]

Another post suggested pulling plug wires, one at a time, as an ignition test. I believe this could be harmful for this reason. These coils are fired by a solid state module, and then each coil fires two plugs in series. When you pull just one wire, that coil loses a conduction path for the high voltage discharge, two plugs now fail to fire. But worse, the collapsing magnetic field energy must go somewhere. Voltage rises to extreme levels, way past the normal plug fire level since one plug wire is just out there in space, nowhere near a ground point. This voltage rises till somewhere it can find a path to dissipate. This final discharge point might be just corona discharge into the air. But it might be a path through the weakest part of the solid state ignition module, causing damage.
I always believed the correct method is to ground the plug wire during a test, to allow a more normal path for discharge, and allowing the companion plug to fire normally. I sometimes us the springs out of old ballpoint pens to slip onto the plug, and then attach the plug wire. Then using a jumper wire attached to a ground, I can sequentially ground each plug by touching the exposed spring. It is also safer as I don't get zapped accidentally.
There are a lot of experienced members on this forum. I'd appreciate any comments (even contrary opinion) to confirm, or dispute, this scenario.

[4given]

How about one of these?

[OldguyGlen]

Thanks for contributing. Those testers help show if there is juice in the wire, often helpful. But they don't tell about fouled (shorted) plugs. But being able to force a short with a jumper lets you know if a cylinder is functioning properly or not. Helps to detect compression, or fuel problems besides just plug trouble.

[4given]

Sorry, that went way over my head.

[DenverWinger]

Most us old folks have a timing light laying around. Use that to check ignition. Clamp on all four (or six) wires one at a time and see if it flashes.

[Rambozo]

Another post suggested pulling plug wires, one at a time, as an ignition test. I believe this could be harmful for this reason. These coils are fired by a solid state module, and then each coil fires two plugs in series. When you pull just one wire, that coil loses a conduction path for the high voltage discharge, two plugs now fail to fire. But worse, the collapsing magnetic field energy must go somewhere. Voltage rises to extreme levels, way past the normal plug fire level since one plug wire is just out there in space, nowhere near a ground point. This voltage rises till somewhere it can find a path to dissipate. This final discharge point might be just corona discharge into the air. But it might be a path through the weakest part of the solid state ignition module, causing damage.
I always believed the correct method is to ground the plug wire during a test, to allow a more normal path for discharge, and allowing the companion plug to fire normally. I sometimes us the springs out of old ballpoint pens to slip onto the plug, and then attach the plug wire. Then using a jumper wire attached to a ground, I can sequentially ground each plug by touching the exposed spring. It is also safer as I don't get zapped accidentally.
There are a lot of experienced members on this forum. I'd appreciate any comments (even contrary opinion) to confirm, or dispute, this scenario.

Grounding through a load would be ideal, but there is a snubber circuit to protect the output transistors. So while I wouldn't ride around with a plug wire off, the short time for testing is no big deal.

Open circuit would have the highest voltage but lowest current, while grounding would have the lowest voltage, but highest current. Either extreme is a bit hard on the system, but nothing it can't handle for short periods.

[LAB3]

It's just a matter of good practice to ground the wire with the plug attached. If the spark doesn't jump the gap you can try another plug and work from there, much closer to a "real world" scenario.

[ct1500]

When you pull just one wire, that coil loses a conduction path for the high voltage discharge, two plugs now fail to fire.

That is false and Internet myth. Just for kicks one day I left all plug wires off on the left side. The engine started and ran on the right three cylinders. Your general concern could be warranted if these were HEI coils with high firing voltages but they are not.
There is no evidence for your conclusion that it is detrimental to the electronics. A real world scenario is that plug wires do fail, break and sometimes come loose with no resulting damage other than a dead cylinder.

[dingdong]

When you pull just one wire, that coil loses a conduction path for the high voltage discharge, two plugs now fail to fire.

That is false and Internet myth. Just for kicks one day I left all plug wires off on the left side. The engine started and ran on the right three cylinders. Your general concern could be warranted if these were HEI coils with high firing voltages but they are not.
There is no evidence for your conclusion that it is detrimental to the electronics. A real world scenario is that plug wires do fail, break and sometimes come loose with no resulting damage other than a dead cylinder.

I wonder how that fable ever got started. You are correct, both cylinders don't fail to fire.

[OldguyGlen]

Been doing more research. This is a '80 GL1100, other (newer models) might differ. Dual fire coils come in two versions, series wired with 1 secondary winding wired to a spark plug at each end. Firing current flows to one plug, through the engine, and back through the second plug. The other version has 2 secondary windings in parallel, each grounded at one end. The other ends are each wired to a separate plug. Firing current flows simultaneously in each winding, out to the plug, and back through the engine ground. My GL1100 has the series format. Ohm meter test shows 20k ohms, Plug wire-to-Plug wire. No connection to ground. Open circuit at one end (plug wire in midair) would definitely put a strain on the circuit. In order for the companion plug to fire, the current would have to jump to ground somewhere via a weak insulation point. While this might be tolerated briefly without serious damage, I would never deliberately do this. In the old breaker point systems I often took shortcut test procedures without harm. But with newer higher voltage coils and solid state igniters it would seem risky. The snubber capacitors are designed for the inductive kick of the primary circuit, but can't handle the kilo volt levels of the secondary voltage looking for ground via the weakest link. Even in the two-secondary coil designed, one plug certainly would fire, without the companion plug, on its own winding, but the mid-air wire still creates a strain on the system due to the firing energy needing a way to dissipate without a plug gap or other ground path. I know that wires fail, wire caps fall off, etc. and systems survive. Maybe the coil design has an internal small gap to pass the current in a free wire condition. I don't disagree with members who have witnessed their own experiences. Also note, my original post and thread title may have suggested a goal of deciding whether there is juice in the plug wire or not. There are easy ways to test that, per replies above. But I was also probing ideas about grounding a plug to help diagnose weak cylinders due to multiple possible causes like low compression, carb problems, or fouled plugs. Identifying the weak cylinder via rpm drop is a first step in locating those other problems. In those situations I will use the ground the wire rather than lift the wire technique. I appreciate all replies as this is a great forum to share info and experiences.

[Jemayo]

Right now, my 83 wing APPEARS to be firing on 1 cylinder, I figured this by pulling 1 plug at a time (CYL 1 bike died, 2-4 no change) I hate doing this diagnostic because YES it could cause damage but it shouldn't hurt your wing to much.