Intermittent Spark on One Cylinder

Copperhed51 · May 21, 2008, 04:05:09 PM

Alright, so the right cylinder on my 91 GS500E is losing spark after I ride it for a few minutes. I can't figure out what the problem is so I'm looking for any advice anybody can give me. I take the bike out of the garage, start it up and go ride and all is well for the first 5 minutes or so. Then all of the sudden I lose a ton of power and get a bunch of backfiring when I'm off the throttle. The bike won't idle under this condition. So I usually limp it home slowly and get it in the garage and test for spark and the left cylinder is fine but the right has no spark. Then I can take the bike out a few minutes later and sometimes it'll run fine for 30 minutes. I've tested the coil and plug wire and all seems fine there. I'm having a little trouble tracing other wires that might be involved and am a little uncertain what I'm looking for. Let me see if I have this right.

Battery provides power to coil which builds power that is released to the spark plug whenever that little rotor thing on the right side of the engine spins past the pickup for each respective cylinder. Now somehow there is also some igniter or exciter box or something that is associated with all of this. Can anybody explain the ignition system to me a little better and/or give me any suggestions on what they think the problem is or any things I should check? I'm pretty much lost at this point and am getting tempted to start replacing everything that involves the ignition on the right cylinder. Maybe the timing is jacked up or the gap on that rotor is wrong? Are these possibilities..........I'm frustrated.

Thanks in advance,

Ryan

sledge · May 21, 2008, 04:33:02 PM

Insulation on the copper wire in the ignition or pickup coil could be breaking down as the coil warms up in use. When cold and under static conditions they might test ok, but the fault might only develop after a period of time in use. The only real way to be sure is to substitute the suspect parts with ones that are known to be good.

ben2go · May 21, 2008, 07:41:47 PM

My thought also was a bad pick up or coil.

The Buddha · May 21, 2008, 08:38:41 PM

The sledge is on the nose here.
I had that thing go on my bike, and You can start it and in under the 10 mins it takes to act up, you get on the highway and run WFO ... and the damn thing will run and run well, Just never drop below 5K and it will run till you run out of gas. Drop down under 5K and it will instantly drop 1 cyl.
Yea, the part is on the motor, under the round hatch by your right foot, and that round plate and wiring all need to be replaced.
Cool.
Buddha.

Copperhed51 · June 09, 2008, 07:34:51 PM

Well, I may have figured this problem out but I'm not sure. Here's where I'm at.

I switched the right and left coil, plug, and wire to see if the problem would switch sides as well. The right side was still the one with the problem. So, that rules out the coil, wire, and plug.

Next I tested the signal generator for resistance and all checked perfectly there according to the numbers in the book.

Next I decided it's either the igniter (which I have to take to Suzuki to get tested) or just some kind of bad connection somewhere.

So, I started checking resistance in the wires in the system. I found that the black/yellow wire that connects the coil to the igniter has variable resistance between 5 - 280 ohms. I can't for the life of me figure out why that is and I screwed with the thing for like 25 minutes trying to get a consistent reading and I can't. So, my current theory is that I just have a bad connector or wire there and plan on replacing that and with any luck, my problem will be gone.

I am an airline pilot sitting low on the seniority list which means I have a really crappy schedule and am hardly home. Hopefully I can get this thing licked in the next week or so. Gonna be such a relief if this fixes it. Thanks for all the suggestions.

The Buddha · June 09, 2008, 08:03:38 PM

OK how did you switch the crank trigger that sledge and ben and I referred too ... its also called the pickup coil, but its fitted to the crank ... not saying there isn't a way to swap it from left to right but just asking how you swapped what ever ...
BTW your swap of the coil+wire+plug pretty much confirmed the crank trigger as the issue ...
However to swap it and run it reliably this is what you have to do ...
I think green and grey are the colors in the 4 wire pigtail from that piece to the wiring harness. The other 2 are black and black with red tracer maybe ... one is ground, other is oil pressure switch, you make 4 spade connector wire bits about 1 foot long with male spade on 1 side and female on other side. All of them should be unsheilded. Run the green to grey and vice versa but the other 2 run them straight through to the wiring harness ...
Make sure you dont screw this up. Green from pigtail goes to grey in wring harness and grey from pigtail goes to green in wiring harness. The other 2 go straight on.
Now your left trigger is going to fire the right coil using everything else that the right is using - aka what is in the Blackbox and the rest of the wiring harness. So run the right coil's plug cap to the left cyl. Now if your problem persists with the same cyl as the problem then ... the crank trigger is bad.
BTW you can also de solder and move the trigger pick up's across and that will do the same thing.
Anyway ... I trouble shoot my virago 535 this way few years ago. And it has 5 wires ... PITA.
Cool.
Buddha.

The Buddha · June 09, 2008, 08:07:05 PM

Dude 5 mins of engine heat are giving you a bad connection ... no ... quit shooting in the dark ... you crank trigger is the only part that can get f&*ked up with that little heat.
BTW it produces suddenly low readings even when good. It will be 280 for 20 seconds, drop to 20 in a flash and back to 280 as an example ... inductive pickup's do that. They see the nose of the advancer and drop to a lower resistance.
Cool.
Buddha.

Copperhed51 · June 09, 2008, 08:46:37 PM

Quote from: The Buddha on June 09, 2008, 08:07:05 PM
Dude 5 mins of engine heat are giving you a bad connection ... no ... quit shooting in the dark ... you crank trigger is the only part that can get f&*ked up with that little heat.
BTW it produces suddenly low readings even when good. It will be 280 for 20 seconds, drop to 20 in a flash and back to 280 as an example ... inductive pickup's do that. They see the nose of the advancer and drop to a lower resistance.
Cool.
Buddha.

Guess I wasn't clear enough when I explained the wire I tested. The wire that was giving me variable resistance readings was not connected to anything when I tested it. I just tested from one end of the wire to the other and couldn't get reliable readings. The only thing that should have been providing resistance during this test would be the wire itself and the connectors on the ends. I'm gonna go ahead and replace this wire just to eliminate it as a possible cause. However, I think you're probably still right about the signal generator. I rode the bike around tonight without the cover on that which kept it much cooler and the problem took a really long time to present itself. So, keeping that part cooler seemed to prevent the problem.

I'll re-read the method you suggested to test it and I'll try that. My clymer book gave a method to test the signal generator by testing resistance between a few different wires and when I did that, everything checked fine. I did it numerous times with the bike cold and working properly, and hot and not working properly. I just ordered a new one and I'll put it on the bike and hopefully it'll work. $125 for the stupid part but oh well.. Sounds like you're pretty sure of it. Thanks again.

Copperhed51 · June 18, 2008, 09:30:19 PM

Ok, so I replaced the signal generator and went and rode the bike around the neighborhood. Everything worked perfectly....for a few minutes. Then, just like before, one of the cylinders dropped and the bike lost all power. So, I still haven't replaced that wire I was talking about, but I'm gonna do that and see what happens. Sucks that I can't return the $125 part I just bought.

The Buddha · June 19, 2008, 07:12:50 AM

Oh crap ... very very sorry. Open wire with fluctuating resistance ... damn, you replace it and try, but that is a totally new one to me, never ever heard of it ... very sorry again.
Cool.
Buddha.

The Buddha · June 19, 2008, 07:14:42 AM

That signal generator has a good street value, and most GS'es tend to eat them between 25-35K, and it cannot be swapped in from another bike, so You're sitting on a part you'd need in future. I know small consolation, sorry again.
Cool.
Buddha.

Copperhed51 · June 19, 2008, 02:23:14 PM

No worries. Just gone done replacing the wire. Rode the bike for about 25 minutes, no problems so far. I'm gonna let it sit for about 20 minutes and let the heat sink into all the wires, coils, signal generators and whatever and go ride it again. If it still works in 20 minutes, the wire was the culprit. I should have just replaced the wire before buying the signal generator but I'm lazy and stupid so it's my fault. Still appreciate the advice. Keeping my fingers crossed that the problem is nixed. This has been so frustrating. I'm getting laid off from my job at the end of the month so I need to get the gas mileage from the GS.

Copperhed51 · June 19, 2008, 08:54:51 PM

So, I let the heat sink into everything, rode the bike again for another 15 minutes or so (then the rain came) and everything worked perfectly. Now all I need to do is make sure the chain tension is right, put a missing headlight mounting bolt in and the bike is ready to ride for a long time hopefully.

ben2go · June 19, 2008, 10:43:15 PM

Quote from: Copperhed51 on June 19, 2008, 08:54:51 PM
So, I let the heat sink into everything, rode the bike again for another 15 minutes or so (then the rain came) and everything worked perfectly. Now all I need to do is make sure the chain tension is right, put a missing headlight mounting bolt in and the bike is ready to ride for a long time hopefully.

We ain't had rain in my area since April.

When I walk across my yard it sounds like I'm walking on bags of chips.

Copperhed51 · June 20, 2008, 07:22:11 PM

Feel free to come steal some of the rain from the midwest. We have way more than we can handle.

ben2go · June 20, 2008, 07:30:00 PM

Quote from: Copperhed51 on June 20, 2008, 07:22:11 PM
Feel free to come steal some of the rain from the midwest. We have way more than we can handle.

Yes, I feel so bad for the people stuck in the flooding.I hope everyone pulls thru.I wish there was some thing that could be done to prevent it from happening again.It's happen 3 times that I can remember maybe more,and I'm only 31.

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Intermittent Spark on One Cylinder