Losing spark in one cylinder after warming up

[DesertFox]

I discovered my right cylinder on my '97 GS500e was receiving no or very intermittent spark yesterday and, after following many helpful posts and articles here, have traced it down to the coil and/or the plug wire itself.  I pulled the tank and right coil and discovered both the coil and plug connector ends of the wire were fairly loose.

Using this handy method http://gstwins.com/gsboard/index.php?topic=19546.0 I tested the right ignition coil.

Primary test (Black/Yellow & Orange/White) was within spec.
Secondary test (Black/Yellow & Spark Plug Wire) had no connectivity at all.  After removing the wire from the coil (since it felt like it was falling apart anyway) I tested again from black/yellow to the wire threads at the end of the coil (where the wire came out of).  This time it registered an expected resistance reading, which leads me to believe the coil itself is still good.

So, it appears I have a failure inside my plug wire itself.  Which finally leads me to my "quick" question...

Should I have continuity (and be completing the circuit) in this photo?


Hoping I can get this sorted out today.  Thanks in advance!

[the_63]

In my very limited experienced opinion, I would say yes.

[DesertFox]

That's where I'm at.  it makes sense that there should be continuity through the entire connection.  Currently there is none.

[lucas]

There must be continuity in that wire in order to deliver a spark.

should be an easy fix, good luck!

[DesertFox]

I think the only fix is going to be replacing the wire entirely.  Hopefully finding a suitable replacement isn't difficult.

[the_63]

There are a billion spark plug wires on the eBay

[DesertFox]

I'm aware of that. Hoping I can source something local and have this fixed today; this limits my options.

[fetor56]

For curiosity slide the rubber seal down and check the connection between the wire and the plug cap....it's possibly loose.

[DesertFox]

I actually disassembled the whole cap (as much as I could) when I suspected it to be the issue.  The bare wire without the cap or coil has full continuity.  There's a break somewhere inside the plug head itself.

Just got back from my local cycle shop and they had NGK replacement "universal" plug heads for $3.95/ea.  We'll see if that does the trick.

[DesertFox]

After rebuilding the cable I was able get a nice clean spark out of the plug.  Thought the problem was fixed, it was idling smooth and the throttle response was good, so I let the bike warm up a bit more while I got my gear on to go for a test ride, and it died as soon as I pulled it out of my garage.  Started up and again the right cylinder wasn't firing.

I'm suspecting the coil is bad but only after it warms up.  Does that sound right?

[sledge]

Absolutely.

You will have a dry joint/bad connection or a cracked wire within the coil, it gets hot, it expands, things move slightly and it causes an open circuit. Then when it cools things shrink back into position and the circuit is remade.

Take it off the bike, put it in a oven on a low heat and then check it again when its warm. You will almost certainly find its gone o/c.

[DesertFox]

Thanks!  I found a good used set of coils on ebay for $30 shipped, should be here next week.  I'll still probably give the oven trick a go, just for my own peace of mind.

The biggest bummer from all this is I was intending to be out riding in this gorgeous PNW sunshine today!

[DesertFox]

Unfortunately I replaced the coil and my problem still exists the right cylinder stops sparking after it warms up.  The left cylinder still fires great.

I ran resistance tests while the bike was warm and the spark issue was actively happening.  Ohm readings are written on the diagram:




The right cylinder is slightly above the 18k-30k range, but I highly doubt that would cause absolutely 0 spark, so I decided to try a little unconventional test.
Using some spare wiring, I performed a spark test with the B/Y and W wires switched, effectively switching the cylinders:

(It's ok to be jealous of that stellar wiring...)



Once switched, the problem followed.  The right cylinder fired a nice blue spark, the left was dead.  Returned the circuits to normal and the problem went back to the right cylinder.  This tells me everything from the plugs back to the Ignition Control Unit is in working order.  Based on the diagram, my problem is either rooted in the ICU or traces back to the pulse/signal generator.

The questions I have are:
1. Would a dead/dying pulse generator cause a single cylinder to stop firing?
2. Is it more likely the ICU is not doing its job, and if so, is there any other troubleshooting I can do on it aside from switching it out with another one?

[DesertFox]

I may have answered my own question after doing more forum searching.  Sounds like the signal generator failing once heated up is more common than I thought and could definitely be causing the issue.  A lot of the links I've found that may guide me have been broken, but I'm going to continue searching.  If anyone has any references to other posts or pages that cover diagnosing this thing, it would be greatly appreciated.

[DesertFox]

Pretty sure I've correctly traced this thing back to the pulse/signal generator thanks to Kerry's awesome posts like these: (http://gstwins.com/gsboard/index.php?topic=65053.msg777501#msg777501, http://gstwins.com/gsboard/index.php?topic=5500.msg45007#msg45007).  Looking for input from experienced folks to make sure I'm coming to this conclusion correctly.

I performed all resistance tests starting at the connectors near the ICU and working back toward the signal generator coils.  At each step, the brown to black/blue was infinite resistance (signified as a | on my particular multimeter).  The green/white to black/blue was within spec, measuring between 280-300 depending on when it was cold or warm.  The last test I did, both while the bike was cold and warmed up, is the leads on the generator coils themselves:

Black/Blue and Green/White - within spec:


Black/Blue and Brown - infinite:


Based on this info, am I correct that the coil with infinite resistance is dead and needs replacing?  Just trying to save myself more heartache of replacing a part I think is the root of the problem.  Is it possible to get the individual part and do a little soldering, or better to just order a replacement pulse generator?

[lucas]

As far as I know you can only obtain the entire signal generator with the two sensors and back plate.

There might be someone on this forum that has an old signal generator with a working front sensor who could sell it to you. 

[DesertFox]

Thanks, I figured that was the case, but being a bit of a n00b in the area of automotive electrical wanted to get a 2nd opinion.  Got a couple possibilities for a replacement part I'm looking into.  I also have a friend who's great with electronics that wants to open up the individual dead coil and see if we can repair it... maybe I'll do that AFTER the bike is back on the road...