Ignition Problem?

I noticed this on Sunday when riding with Jim Henke, Dave Berzins and Tim Graham. Took the car yesterday but rode the bike again today and noticed the problem again. It usually happens when riding around a constant 70 - 75 MPH. Also in lower gears at similar RPM (4000-4500) I back off the throttle just a tiny bit and the engine feels like someone completely shut the key off, then before I can react it resumes, but with a semi-violent surge / jerk. This is much larger than the subtle lean spot issue these bikes are known for. As I'm riding to work I'm wondering about the fuel pump, possible vacuum leak, spark plugs (48K on them), injectors gummed up, what could it be? Then I happened to be looking at the dash when it did it again and notice the tachometer, basically shuts off (drops to "0"), and then bounces back in sync with the power surge. Now I'm pretty sure it's an ignition problem, rather than a fueling issue, based on the tach observation assuming the ignition also powers or sends a signal to the tachometer. Also the sudden onset / recovery better fits some kind of intermittent electrical issue.

I'm going to check all the obvious stuff, Coil, battery & ground connections, the coils themselves and the spark leads. I've seen some similar older posts but not exactly what I'm experiencing. There's no "FI" light (though I've not checked for codes), the bike has about 148K on it now and other than some early (~20K) problems with a MAP sensor error, this is the first time I've had a running issue with it.

Wondering if there's any experience with this problem to draw on?

I was thinking fuel pump but the tach thing has me thinking ground,

Here's an article related to blown fuses but might be one place to start.
https://www.st-owners.com/forums/showthread.php?77922-ST1300-Intermittent-blown-fuses-caused-by-wire-rub

Hi Jeff,

My limited experience with ignition problems is they are significant enough to blip the tach and stumble a bit at the problematic RPM range, but the symptoms you report seem more severe than a simple ignition coil issue. Yours sounds more like a complete power loss for a split second, like a loose battery cable or main power switch glitch. I'd check those kinds of things first. Also, in that harsh climate you live in, with those 10 degree yearly temperature swings, coil failures are probably fairly rare. But you do have the salt air to deal with, so checking for corrosion on the high current paths would be a good idea too.

To me the tach zeroing out points to a ground issue in the front wire harness or a short to ground in the kill switch harness. If it was on the positive side of the battery the intermittent short would blow fuses or melt wires. An intermittent short seems to be turning the bike "off". A clue would be if the instruments black out when the fault occurs.

dwalby said:

Hi Jeff,

My limited experience with ignition problems is they are significant enough to blip the tach and stumble a bit at the problematic RPM range, but the symptoms you report seem more severe than a simple ignition coil issue. Yours sounds more like a complete power loss for a split second, like a loose battery cable or main power switch glitch. I'd check those kinds of things first. Also, in that harsh climate you live in, with those 10 degree yearly temperature swings, coil failures are probably fairly rare. But you do have the salt air to deal with, so checking for corrosion on the high current paths would be a good idea too.

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Thanks Doug, agree. Can't see how loosing only one coil would cut the power so completely as well as killing the tach. Gotta be something further upstream I think.

dduelin said:

To me the tach zeroing out points to a ground issue in the front wire harness or a short to ground in the kill switch harness. If it was on the positive side of the battery the intermittent short would blow fuses or melt wires. An intermittent short seems to be turning the bike "off". A clue would be if the instruments black out when the fault occurs.

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Holy cow!, I think you may have hit it on the nail dduelin! I've had trouble with the kill switch getting cruddy and causing problems like this before. I'd forgotten about that, until you mentioned it. I also know that hitting the kill switch will cause the tach to drop to zero, even if the engine's still in gear and being spun by the transmission / rear wheel, so it all fits. This is my #1 suspect now! Thanks

Hope its just a cruddy kill switch Jeff, can't get much easier than that. If that doesn't fix it, the only other comment I wanted to make is an intermittent open would also kill things just like an intermittent short would, so I wouldn't rule out the hot side for loose connection problems if you have to dig into it further.

Jeff I hope it is just the switch that needs to be cleaned. Are you sure Tim did not mess with your bike??

970mike said:

Jeff I hope it is just the switch that needs to be cleaned. Are you sure Tim did not mess with your bike??

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I'm thinking he put some Habanero Pistachio crumbs in there!

wjbertrand said:

I'm thinking he put some Habanero Pistachio crumbs in there!

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Wow... all 10lbs... what kind of pace did you set!

Mark said:

Wow... all 10lbs... what kind of pace did you set!

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Pulverizing obviously....

Sounds like an intermittent open - not a short. I don't know how the kill switch works - I assume it opens the ignition circuit thereby shutting down the bike. It is curious that the problem seems to be throttle position sensitive. If indeed the whole bike (instrument panel) momentarily goes out, then yes, I lean toward the kill switch. if not, it is probably a loose/corroded ground that is affected by vibration. When I roll off the throttle the bike invariably feels smoother - so maybe it is a lack of vibration that is causing the ground to open.

All I've noticed so far is that the tach drops to zero, the rest of the panel continued to stay on. This also the case when you deliberately switch off the kill switch. Fiddled with the switch last night on the way home to verify this behavior. Interestingly I only had one obvious and maybe one additional cut-out last night. Thinking just operating the switch a bit (I almost never use it) helped. I did take apart the switch pod and squirt out the switch with contact cleaner, working it back and forth last night but had to to take the car today for work reasons.

Well, it's not the kill switch. The problem resumed today in spite of the cool morning temperatures and a topped off fuel tank. I did refine my observations this morning however. First it happens exactly at 4,250 RPM, but only when decelerating or using extremely light throttle. If I just let the bike coast from say 4,500 RPM down through that range, without touching the throttle (completely closed) the tach needle will drop / swing rapidly down and back up a few times right as I hit 4,250. Of course when coasting I don't feel the surging or bucking. I can accelerate through that RPM with no issue at all. I also proved that it doesn't matter what gear the bike is in, I'll get the same behavior in 3rd, 4th, or 5th at that specific RPM. Weird.

... so, like the fuel is being cut off?.... then back on...

ECM contacts?

Mellow said:

... so, like the fuel is being cut off?.... then back on...

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Maybe, but how to explain the tachometer behavior?

Mark said:

ECM contacts?

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Could be, obviously I've got some deeper digging to do.

wjbertrand said:

Maybe, but how to explain the tachometer behavior?

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The only sensors that could gauge engine speed (cam and ignition pulse generators) feed the ECM and I don't think there's anything that branches off the coil lines. That makes it a pretty good bet that the tach is driven separately by the ECM.

It's possible that one of those sensors is becoming flaky, but I'd hope that the computer would catch that and throw a fault code. The TPS is a possibility, but again, I'd think that would result in a fault code.

My money is on the problem being in the path that powers the ECM. Recovery from this while underway without any help from you suggests that the ECM is losing power, regaining it and then starts adding fuel and fire the coils after it detects that the engine is turning. In other words, a momentum-driven bump start. If you have something that can record voltage over time, the ECM feeds a 12V line on the diagnostic connector that would be perfect for testing this theory.

I'd go through the ECM's power path with a fine-toothed comb, making sure all of the connections are clean and tight and maybe replace the main stop relay. I'm pretty sure the bank angle sensor circuit can be ruled out since that condition requires the ignition be cycled on and off to clear.

Hope that's of some use.

--Mark

Thanks Mark, I've got no way to record voltage over time. But the idea of checking all the connections to the ECM makes sense. I know if I flip the kill switch, I'll see the FI light come on and go through its start up delay, same as when first turning on the key. I think this is the ECM resetting after a complete power off. I'm not seeing this the FI light coinciding with these episodes, which I think I should if the ECM lost power momentarily.

I'm also pretty suspicious of the TPS. I watched all the other dash displays during these episodes and nothing else is disturbed from what I can tell, no FI lights, no clock resetting, etc.. Only the momentary loss of power and tach function which are happening simultaneously. The TPS is suspect because I only see the problem with the throttle closed or only very slightly open. With a larger opening the bike accelerates trough that RPM range with no issues. There seems to be a composite effect here - both a very specific RPM and a closed or very nearly closed throttle have to be present to see the fault.

wjbertrand said:

Well, it's not the kill switch. The problem resumed today in spite of the cool morning temperatures and a topped off fuel tank. I did refine my observations this morning however. First it happens exactly at 4,250 RPM, but only when decelerating or using extremely light throttle. If I just let the bike coast from say 4,500 RPM down through that range, without touching the throttle (completely closed) the tach needle will drop / swing rapidly down and back up a few times right as I hit 4,250. Of course when coasting I don't feel the surging or bucking. I can accelerate through that RPM with no issue at all. I also proved that it doesn't matter what gear the bike is in, I'll get the same behavior in 3rd, 4th, or 5th at that specific RPM. Weird.

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Well, you could always keep it under 80MPH and ride like a grandpa but what fun would that be???

I don't see how an intermittent open or short could happen repeatedly at 4250rpm. Sounds like a deliberate mapping/calculation glitch. I'd concentrate on an ECM issue of some kind first. Do you have anyone around you could go and swap ECM's for a day or two?

The only other problems I can recall off hand that had an RPM component to them were issues dealing with the knock sensors but those issues would trigger fault codes and the service manual refers to having to be at or above 3900 rpm for ten seconds in order to set the fault.

Side note: Curt and I swapped ECM's back in 2011 in order to try and explain why he was getting relatively poor fuel economy compared to me whenever we were riding on trips together. Turns out that swapping the ECM in this case didn't solve the problem and we never got around to swapping the units back again before his crash...