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Discussion Starter #1 (Edited)
Sunday couple weeks ago, I promised myself to ride 100 miles in a single day. Considering the reliability record of this $1500 Duc so far, the projected outcome was unclear. Google maps claimed it was 54 miles to Hell so there I went and back I came with no problems. Chilled out for a bit, but then discovered that thanks to taking the little roads, I'd only ridden 94 miles. Couldn't have that, so headed out into the local countryside. At 101 total miles, the engine went nuts, afterfiring, backfiring, sputtering and producing about 0.3 horsepower. I limped toward home at ~3 mph, when after about 5 minutes, it suddenly began running fine.

:confused: Connectors? In my garage, all the wire wiggling I could manage wouldn't cause the problem to happen again. Temperature sensors? Engine ran well enough with them disconnected. Plugs were dark, but they've always been dark. Hummm. I checked the numbers. Champion RA4HC. Looked in the online Champion guide. Dumbass previous owner put in **racing** plugs - must be better since it's RACING, right. So the plugs loaded up on the preceding cruise? Stuck in the proper RA6HC, and she runs like a top for the next couple of weeks.

Sunday 2 days ago ... rode to Hell and back again. No problems, perfect ride. Chilled for a couple hours, then headed across town for a baby shower. 7 miles later, the engine quit cold. Differently this time, no sputtering, no fussing, just f'ing quit. Rolled to a stop 6" off one of the busiest local roads and tried to restart. After a couple of tries, it would idle, but only idle. Only a slight increase in throttle and it would quit dead. Clean cutoff. But I noticed each time it happened, the tach would instantly drop to zero. Later, presumably as the engine cooled (it was a hot day, much warmer than 2 weeks before), I could coax it to 2500 rpm before it cut out. Same thing, the tach instantly to zero before the engine wound down. (Other instrument lights, such as oil pressure and neutral stayed live however). By then, the tow truck arrived. When I got it home, it ran perfectly (of course).

Ideas?

Or shall I limit my daily mile total to 99?
 

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The first problems description rings the "fuel delivery" bell. Base on that I would check to make sure the fuel and the vent lines weren't pinched and the tank isn't under a vacuum. I'd also replace the fuel filter and clean the fuel pump screen. But...based on the second description...the problem sounds abrupt, suggesting electrical. Based on the second description, I'd check/clean the battery connections and check all the grounds.
 

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There are 2 relays under the seat. Both ECU controlled. One commands the radiator fan, the other gives 12V to the fuel pump and the coils. You might want to swap those 2 to see if the problem goes away.

And yes, judging by the tach dropping, it sounds spark or ECU related. So it could be a connector. Maybe even a faulty kill switch? I know a few guys in here have found their kill switches needing cleaning up (bad connection).
 
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Discussion Starter #4
There are 2 relays under the seat. Both ECU controlled. One commands the radiator fan, the other gives 12V to the fuel pump and the coils. You might want to swap those 2 to see if the problem goes away.

And yes, judging by the tach dropping, it sounds spark or ECU related.
Good tip. I did the swap, but am a little skeptical. Here's why. From the wiring diagram, the relay on the LHS controls the injector, coil and fuel pump power, plus connecting to the ECU input #23. With the key on, unplugging this relay def kills power to the pump. The relay on the RHS has no obvious connection to the fan, but is connected to ECU inputs #4 and #35. Too, there is a connection to the voltage regulator. It's not clear, but perhaps it's the fault sense wire from the stock regulator which doesn't exist on my present one. The function of the RHS relay seems to be interlock-related.

With both relays in place and apparently working, turning on the key causes the fuel pump to come on, run for a few seconds, then shut off. Oddly, with the RHS relay removed, turning on the key still starts the pump, but *it doesn't shut off*. Swapping the two relays with each other didn't change these conditions.

I wish I had the pin-out logic for the ECU to diagnose further.
 

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Did you wear a crucifix when you went to Hell ? I think you need to find a priest.
 

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Before moving on from the simple fixes check the relay near the headlight and under the removable cover to the left of the gauges.

I had all sorts of random starting and stalling issues on my ST4S before noticing corroded connections on this relay.
It was an instant fix after weeks of trying to replicate symptoms and getting stranded.

Quite a bit of wet weather can get up under that area and create issues.
I also shifted mine further away from where the elements could get at it and have had no further probs.
 

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Does sound electrical, I would also check the fuses under the seat for the ignition coils and ECU.
Could also be a failing crank angle sensor or it's wiring.
 

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Discussion Starter #10
Before moving on from the simple fixes check the relay near the headlight and under the removable cover to the left of the gauges.

I had all sorts of random starting and stalling issues on my ST4S before noticing corroded connections on this relay.
It was an instant fix after weeks of trying to replicate symptoms and getting stranded.

Quite a bit of wet weather can get up under that area and create issues.
I also shifted mine further away from where the elements could get at it and have had no further probs.
This bike shows hardly any sign of being wet or corrosion of any kind. Yet with great skepticality, I checked. The big black 3-pin relay was clean as a whistle and the bike is live with it removed. The little yellow 40A one however had some corrosion and the plug was not fully seated onto its spades. Pulling that plug kills *everything*, which doesn't match my symptoms, but who knows what happens if just one pin is not making good contact. Even if it's not my problem this time, you likely prevented a future failure.

Good call!
 

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Isn't Purgatory in New Mexico? That's kind of inconvenient.
 
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Discussion Starter #14
Failure #3

The good/bad news is that I don't have to ride all the way to Hell to get the failure. In the week since the last one, I put it on my lift and:

1) Swapped the under-seat Bosch relays with each other.
2) Pulled apart all the connectors I could reasonably get to, sprayed with contact cleaner, coated with dielectric grease and reattached.
3) Replaced the vertical cylinder water temperature sensor that reports to the ECU. (It seems to work since the displayed temps are not significantly changed from before.)
4) Pulled the crank position sensor, checked for crud on it and the flywheel, finding both clean.

This time, I only put the upper fairing back on so I could get to all the pieces easily if/when it failed again. The previous failures both occurred on the second run of the day with 1-2 hours separation and the second, worse than the first, happened on a hot day.

Today the air temperature was ~90 deg F (32 C). I went on a few loops, keeping close to home, at speeds from 25 - 60 mph totaling 15 miles and 20-25 minutes. Water temps were normal and the engine ran well with perhaps somewhat more exhaust popping on deceleration. Then I left it parked in the driveway for 1.5 hours.

Upon restart, the water temperature showed 112 deg F (44 C) so it hadn't completely cooled off. A very short way down my street, there was a brief misfire, so I did a circuit around the immediate block with no problem, then headed out on a main street. 30 seconds later, the engine quit dead.

With a bit of luck, I coasted into a closed-on-Sunday strip mall parking lot and even managed to roll to a stop in the shade of a handy tree. This time, with the fairing off, a few tools, and a DVM I could poke around.

1) Same as before, it would restart, but would quit @ ~1500 rpm. Water temp was ~170 deg F (77 C).

2) Initially, the neutral light was not on in spite of it being in neutral. (The 1998 does not have a sidestand switch). Later, I played with the gear selector and the light came on but the engine still would not run.

3) While the tach would instantly drop to zero, everything else, lights, clock, fuel level, water temp display etc. remained on.

4) As before, with the passage of time, the engine would quit at an increasingly higher rpm. One could say it was cooling off, but the lowest water temp I saw was around 155 F (68 C).

5) I was gradually draining the battery with multiple starts, DVM showed 12.2V early on, but the charging system seemed to be working properly. 5 minutes of fast idle at ~1500 rpm brought it back up to a resting voltage of ~12.5V. That also brought the water temp up to ~185 F (85 C). This rise seemed to have no direct effect on the engine cutouts.

6) The dropouts had no visible effect on the battery voltage. If there was a short to ground, it is not a high current short.

7) Opening the fuel tank cap had no effect.

8) Wiggling wires and connectors had no effect.

9) ~30-40 minutes after the initial cutout, I could coax it to ~3,000 rpm. Sometimes by then, it wouldn't completely die, but miss badly, drop 500 -1500 rpm, catch and then die. In one of these sequences, I heard a loud "clank, clank" that sounded mechanical in nature. Pre-ignition? I don't know, very weird.

10) After ~45 minutes, I was getting tired of this cr*p. It seemed to take 2,000 rpm okay, so I got it moving. Rode on some sidewalks to make a shortcut home. It was missing often, but without drama. Made it into my driveway and shut it off.

I'm sure later this evening, it will run again perfectly - for a while. At this point, I'm leaning heavily toward spark as the problem, and am leaning toward coil/igniter/wiring as the cause, but it still may be an ECU-generated fault code interrupt. Short of replacing stuff until the problem goes away or I run out of money to buy more parts, I'm at a loss of even what to do next. Also, it's not a simple process to test this thing; nor is it without hazard when rolling to a stop in random times and locations. :crying:

On my winter to-do list is replacing the fuel hoses. Perhaps I can see more of the problem once the fuel tank is removed.
 

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Replacing stuff until the problem goes away may not sound prudent but at the point you're at, if it was me, that's exactly what I'd do. Im no electrical expert, so many times over the years I've just had to either replace the most likely component or take it to an expert, and it's way cheaper in the long run to replace components compared to mechanic fees. At worst you end up with some spares. It sounds like a faulty ecu to me. Of course, I would buy used from a bike breaker, a part from a running bike. Many times they advertise these parts as having been tested.
 
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I have been down a very similar path with my 97 ST2. The occasional infrequent misfire, that over many months became worse. I pulled apart every connector, had the ECU in and out numerous times, replaced water temp sensors, plug leads, Crank sensor, endless probing, wiggling, multimeter testing etc etc. then the fault just kind of didn't reappear for 6 months or so. Very unsatisfactory result because I had lost faith in reliability of said machine. Anyways, a couple of months ago it happened again, only this time dropped to one cylinder ( I couldn't even tell if I was losing both or just one before, which made fault finding even harder). Damn, it's back I thought. Eventually the thing stopped all together - I rolled to a stop, tried to restart - flat battery, weird because the headlight seemed pretty bright.
So, to cut a long story short I ended up replacing the reg/rect . This in itself is a long story and 3 blown regulators later all is good with no more issues.
I conclude the following from my recent experience: 1. The headlight is still surprisingly bright with a fairly flat battery - don't let it fool you. 2. I think I may have been suffering from an intermitant low voltage problem all along, that when the ECU voltage dropped to around 11.5-12v it started dropping a cylinder ( coils or injector firing I don't know which. Initially I thought this unlikely,but the way the bike finally died was the same as previous - it just didn't recover like it had before). 3. Only replace the reg/rect with a decent (eg. Shindengen FH020AA) unit - the crappy ones off Ebay cannot handle the high output single phase stator op current that our early STs put out. 4. Replacing/soldering the connectors on the yellow stator op is virtually a necessity - these things are putting out around 38-40A AC. The connectors lose tension and get hot.
The reason I say all this is because I see HiFlite states his "resting voltage"of 12.5. That seems really low to me, should be nearer 14 - 14.5. I wonder if his issue is in fact low voltage caused by a faulty reg/rect (or the wiring). I have mounted a voltmeter now and notice the bike runs nicer with the the new reg. and voltage up. I wouldn't have picked this before my recent "journey".
 

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The reason I say all this is because I see HiFlite states his "resting voltage"of 12.5. That seems really low to me, should be nearer 14 - 14.5.
I agree with your low voltage assessment. I would also point to checking the ECU ground itself. Checking, cleaning the whole bit.

A resting battery should sit around 12.5v to 13.2v with nothing connected to it. Depending on how long it has been off of a charger.

Installed correctly, with a parasitic ECU draw, 12.5v should be the minimum. Once the engine is running, a reading at the battery should indicate somewhere between 13.5v and 14.1 or 14.2V.

Lower than that indicates a charging issue. Could be stator, could be regulator/rectifier. Could just be the wiring from the stator or from the R/R.

That's where I would start after verifying the ground at the ECU........sean
 

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Discussion Starter #18
A resting battery should sit around 12.5v to 13.2v with nothing connected to it. Depending on how long it has been off of a charger.

Installed correctly, with a parasitic ECU draw, 12.5v should be the minimum. Once the engine is running, a reading at the battery should indicate somewhere between 13.5v and 14.1 or 14.2V.
Sorry for being unclear, but the 12.2v was after multiple starts in a short period of time. The second sentence above is what I see under normal conditions. I've already replaced the VRR with a FH020AA, much of the wiring and removed the connector in the "yellow" wires from the alternator.

One thing I need to add to my toolkit is a fuse puller. In the case of a starting or other electrical issue removing the fuse to the headlight would give some extra time for troubleshooting before depleting the battery.

Next:

Upon further contemplation and consumption of craft beer, some new ideas came. The key to inducing these failure is to ride for a while the let the Duc sit for 1-2 hours. While parked, the stored heat from the engine goes largely up, where it heats the tank and the fuel in it. The pump is essentially gasoline-cooled. Say a bearing is on the verge of failing, then the extra heat may cause it to temporarily seize or drag. So, I ordered a new pump.

Furthermore, I walked out of AutoZone with a handful of relays and will order a used coil/igniter from E-Bay shortly. Even if they turn out not to be the problem, having a set of known-good spares for a 20 year old motorcycle is probably wise.

Tomorrow I'll take a "vacation" day, and pull and disassemble the tank hardware.

Thanks to you all for your ideas!
 

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OK, sounds like you've got the voltage aspect well covered. Shame because I was trying to compare/tie my own issues to yours :). Previous to my VRR failing, I had changed the plug leads and crank position sensor. The problem disappeared after that, but deep down I'm not convinced it's fixed for good. Like you I was somewhat at a loss what to do next. On the plus side I can now get the mirrors and all the fairings etc off in under 10 minutes, I've had that much practice! There's lots of threads on strange misfires and similar failures, but no real constant answer. It would be nice to be able to swap out the ECU, but without one available... it's a pricey option. I'd be keen to hear if your new fuel pump does the trick - keep us posted.
 

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Sounds more like a crank angle sensor failing due to heat soak. If that is what's happening you can test by using a heat gun or hair dryer pointed at the sensor whilst idling and see if it cuts out.
 
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