Ignition Problem?

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387
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'06 ST1300A
My money is on the problem being in the path that powers the ECM.
That's seems like a pretty good bet. As the circuit that supplies +12vdc to the ECM also supplies:
  • The fuel cut-off relay.
  • Both ignition coils.
  • All four fuel injectors.
  • The purge control solenoid valve.
  • The exhaust air injection solenoid valve.
  • Both O2 sensors.
  • As well as the +12vdc contact in the red Service Connector.
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.
The bank angle sensor circuit should not be ruled out completely, as this is the circuit that supplies +12vdc to the ECM (and other items noted above). However the bank angle sensor, and wiring to the bank angle relay are probably fine for the very reason Mr. Blrfl mentioned. A faulty relay with dirty/pitted contacts, or a weak contact spring should be considered, the fuse (ABS=Fuse L, non-ABS=Fuse J) and wiring to the relay also bears investigating.

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.
Good idea, if a meter is not available, try hooking up a test lamp, and running it up to the dash area where you can observe the lamp output. With an intermittent loss of power, a LED lamp is preferable to an incandescent lamp, due to the time it takes for the incandescent filament to cool, the momentary drop in power may go unnoticed.
 
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Jeff, the RPM dependent nature of your problem is consistent with an ignition problem I had years ago on a car. Ignition voltage requirement is a function of cylinder pressure, so it typically happens at certain RPMs where the cylinder pressure causes a problem with the ignition spark. This may also explain why its worst when you are decelerating, the engine braking is likely increasing the cylinder pressure.

Fortunately for me, I was able to reproduce the symptoms while parked and just revving the engine, and a friend of mine hooked it up to a scope so we could observe the ignition pulses. Sure enough, one cylinder was intermittent, and it turned out to be a plug wire was bad. If you have any way to test your bike this way, that would be enlightening.

In your case, perhaps both cylinders on one of the coils are failing to ignite, so you get an even more severe symptom, and the tach drops out during that time. If you can get someone to swap coils/wires with you, that would be a good experiment to try. If its something else in the computer/TPS, then I don't know what to suggest for those systems.
 
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wjbertrand

wjbertrand

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Lots of good suggestions guys, thanks. Now to find the time to investigate! The bike has 147,000+ miles on it has been totaled and restored so it's been through the ringer and dirty / corroded connectors are a real possibility. First thing I'll do is disconnect, clean and reconnect all the ECM and coil connections. Looked into replacing the TPS and it turns out you can't buy them separately from the throttle body assembly - $1200 new, and that's discount mail order! :eek: Entire used assemblies can be had on ebay for $90 - $140 and looking at one of the photos I pulled the numbers JT3L and 41110 off the TPS. Googling the first number turns up identical looking sensors for various Honda cars. Can't figure what the second number is, but perhaps it's a lot# or something? Nothing comes up searching it. The good news is that these replacement looking TPSs can be had new for about $15 on ebay. Got that page bookmarked for now until I complete some of the above suggested investigations.
 

Blrfl

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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.
Whether it does a full-on startup may depend on how long the power is out. There may be a capacitor that keeps the processor alive long enough to work through glitches. Having the ECM recover into a pre-start state when the engine was running previously would be a safety hazard. (That's how I'd build it, but I don't run that circus.)

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 fact that just the tach dies leads me to think it's a power problem to just the ECM rather than the entire chassis. The dash stays on but the tach flops to zero because it's no longer getting data from the ECM. (Again, just spitballing.)

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.
It's definitely worth investigating, but if you haven't checked for stored codes, do that before you do anything else. IIRC, the FI light only lights when a fault is present, so there could be some useful nuggets stored away. If it is the TPS, there should be plenty of ammo for the ECM to throw a fit. Most EFI systems have two TPS paths. In most cars it's two separate potentiometers, in the ST it's done with one and lines back from both ends of the resistive path. If they engineered it correctly, fully-closed and fully-open won't be at the ends and the ECM would always be able to tell if they match up correctly.


BTW, be careful about replacing the TPS. There may be a factory alignment and calibration procedure that's not in the service manual, which is why they recommend replacing the entire TB assembly. There's probably no safety hazard if it's out of whack, but the fueling could get weird.

--Mark
 
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This sounds like what I just went through. I found a broken wire attachment at the bottom of the round cylinder the key goes into.
yeah, now that you've ruled out the kill switch, you still haven't ruled out supply voltage issues, right? Is it possible that the RPM where you get the failure is causing a vibration that's momentarily breaking a supply voltage connection? Not sure if that would be consistent with only doing it on deceleration, not acceleration, but the symptoms you're having are still pretty wide in scope so power interruption is still a possibility.
 

bdalameda

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If the kill switch causes the same reaction I would suggest looking at the entire kill switch circuit and connections beyond the handlebar switch itself. Could be a simple connector problem - I have seen intermittent RPM related problems simply due to a harmonic at a certain RPM that makes a poor connection lose contact. I'll bet it's a simple small problem - those are sometimes hard to find. I would pull off all the covers and start wiggling and pulling wires and harnesses with the engine running to try and find it. Look closely at any point on wiring or harnesses that have to bend or flex with steering inputs etc. Could be an internal weakness/break in a wire from 147K miles worth of flexing. Don't forget about sidestand switches and clutch switches as well.
 
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wjbertrand

wjbertrand

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Thanks Karen, gonna wiggle the ignition switch assembly a bit on the way home tonight. Doug and bd, yeah I thought about tracing the kill switch harness / connectors etc. There's nothing obvious on the bit that's exposed with all her clothes still on though. Maybe I'll try wiggling the part of the harness that I can reach a little tonight as well.
 
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Will involve a little pain, but may be your problem as what you describe is very similar / almost identical to the issue I had.

The Ignition wires go down under the LH fairing into a bank of 4 connector blocks covered with a plastic shroud. The plastic shroud is wide open at one end and tight at the other end. Logic would dictate the the open end would face toward the rear of the loom. Alas, this was not the case, resulting in road crap sealing the tight end and creating a funnel for water to sit in. The ignition wire was slowly corroding which creates brief intermittent loss of complete electrical power only to be restored a split second later. Eventually, the wire completely seperated from the plug, resulting in no power to the dashboard or the other systems leaving you stranded at the side of the road awaiting recovery DAMHIK.

Remove the LH fairing and check out the state of the wiring into and out of the bank of plugs.

This is the item to check...

17294.jpg

Cheers
 

Mellow

Joe
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Will involve a little pain, but may be your problem as what you describe is very similar / almost identical to the issue I had.

The Ignition wires go down under the LH fairing into a bank of 4 connector blocks covered with a plastic shroud. The plastic shroud is wide open at one end and tight at the other end. Logic would dictate the the open end would face toward the rear of the loom. Alas, this was not the case, resulting in road crap sealing the tight end and creating a funnel for water to sit in. The ignition wire was slowly corroding which creates brief intermittent loss of complete electrical power only to be restored a split second later. Eventually, the wire completely seperated from the plug, resulting in no power to the dashboard or the other systems leaving you stranded at the side of the road awaiting recovery DAMHIK.

Remove the LH fairing and check out the state of the wiring into and out of the bank of plugs.

This is the item to check...

17294.jpg

Cheers
Wow, I don't think I've ever seen a cleaner pic from that part of an ST, even a new one... sorry for the hijack.
 

Mellow

Joe
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I am going to agree with that sentiment. Do they even come from the factory that clean?
I don't think so... the connectors usually have some grease from the assembly process...
 
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wjbertrand

wjbertrand

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Will involve a little pain, but may be your problem as what you describe is very similar / almost identical to the issue I had.

The Ignition wires go down under the LH fairing into a bank of 4 connector blocks covered with a plastic shroud. The plastic shroud is wide open at one end and tight at the other end. Logic would dictate the the open end would face toward the rear of the loom. Alas, this was not the case, resulting in road crap sealing the tight end and creating a funnel for water to sit in. The ignition wire was slowly corroding which creates brief intermittent loss of complete electrical power only to be restored a split second later. Eventually, the wire completely seperated from the plug, resulting in no power to the dashboard or the other systems leaving you stranded at the side of the road awaiting recovery DAMHIK.

Remove the LH fairing and check out the state of the wiring into and out of the bank of plugs.

This is the item to check...

17294.jpg

Cheers
Thanks, good input. Last night I pulled the ECM and inspected then cleaned the connectors, everything looked perfect though and alas, upon reassembly, no change in behavoir. Of course only after all of this work do I bother to look in the manual only to discover that what I actually cleaned and inspected was the ABS controller:doh1:. To quote the great Nigel Mansel, referring to himself after pulling into the wrong pit at the Indy 500, "what a splendid fellow". I just need a block of time to dig into this thing and it's not likely to be this weekend as I have to go out of town.
 
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wjbertrand

wjbertrand

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Well, still no joy. I've taken apart every connector that carries the tach signal from the ECM (instead of the ABS computer this time!) to the tachometer (thinking there's a relation to the tach behavior and the hesitation drop out), tested both coils, the HT leads to the spark plugs. Also disassembled and cleaned all the harness connectors under the left main faring. I have not found anything the least bit suspicious looking, in fact all the connections looked pristine but the problem persists. I'm going to tear into and test the TPS tonight I think. Except for the very specific RPM (exactly 4,250) where the problem occurs, the symptoms are closest to a bad TPS. Unfortunately you can't buy a replacement TPS from Honda (if that's what it turns out to be) you have to replace the whole throttle body assembly for $1200! Luckily, I think I've found some cross references to Honda car TPSs for as little as $14. Gonna hold off buying until I have real evidence this one is bad. It's really a shame because the bike runs perfect under all other conditions. This one's a real head-scratcher.... :confused:
 
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Hey Jeff, I still haven't heard you report that you've ruled out any weirdness in the 12v supply path. Have you?
 
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wjbertrand

wjbertrand

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Hey Jeff, I still haven't heard you report that you've ruled out any weirdness in the 12v supply path. Have you?
I think if you mean battery and ground connections, all have been cleaned and are solid. Every connection / connector I've looked at appears pristine so far. Nothing I've done cleaning and tightening connections / connectors has made any difference. I wasn't too suspicious of a 12v supply problem in the first place, usually that will cause a host of issues & weirdness in my experience. In this case there are none except for this crap out / hesitation under very specific conditions, i.e. light to no throttle and exactly 4250 RPM, otherwise the bike is perfect.

Last night I pulled the connector to the TPS, cleaned the contacts and reassembled also to no effect testing on my commute to work this morning. Didn't have time to dig deeper but will do so this weekend. Trying to eliminate the simple easy stuff first.
 
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I did have an intermittent engine performance issue, though not a complete loss of power at a specific engine speed, which generated a CEL event. I eventually chased the problem to chafed wires in the wire harness in the seat area. That particular wire harness includes well over a dozen conductors, it's possible that one or more chafed wires could yield the symptoms that you're experiencing.

If you're interested, you can read about it here.
 
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wjbertrand

wjbertrand

Ventura Highway
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I did have an intermittent engine performance issue, though not a complete loss of power at a specific engine speed, which generated a CEL event. I eventually chased the problem to chafed wires in the wire harness in the seat area. That particular wire harness includes well over a dozen conductors, it's possible that one or more chafed wires could yield the symptoms that you're experiencing.

If you're interested, you can read about it here.
Thanks, talk about finding a needle in a haystack though! A couple of questions; first were there outward signs of the abrasion visible on the harness before stripping it back like that first photo? Second, did repairing those wires solve your problem?

I will definitely take a close look at this area tonight.
 
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Out in the garage.
I recently relocated my coils from their stock locations to under the tank. This involved building longer plug wires and a bracket to bolt the coils to. On my first ride, my bike would do exactly what you're experiencing, but only when hitting a hard bump, and with the addition of the CEL coming on for a few seconds. It was bump dependent, not RPM/ throttle position dependent. Turns out, my coils were momentarily losing ground. Bracket fixed, no more issue. You might want to look at how the coils are grounding to the frame.
 
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