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Discussion Starter #1
I was about 15 minutes/7 miles into my ride, cruising around 45 down a flat, straight stretch and my bike faltered for 1-2 seconds. I kept even throttle and it picked up again for a few seconds, faltered, and died.

Coasted onto the shoulder, keyed it off, then back on. Normal so far. Hit the starter and it fired up and died again within a second. Took off my helmet and ear plugs, gave it a good look over and found nothing. I keyed it back on, heard the fuel pump whir, hit the starter and it fired right up and idled fine.

Not wanting to continue heading further from civilization, I headed back home without any issues. I rode 5-10 miles extra around my house without issues. Idled fine at stops, etc.

I've had no issues with the bike to date. Aside from oil/filter change, wheel swap and brake/clutch fluid flush, it's been unmolested this season. Haven't had the plastics off, even. Tank was 3/4 full with fresh gas.

Any thoughts even on where to start looking? I'm pretty hesitant to ride it anywhere now.

Thanks much.
 

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I would start with making sure the grounds are clean and tight, then charging system, battery, regulator/rectifier, connector between r/r and stator.
Good luck .
 

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Yes, and wires to/from ignition switch - particularly the connector for the switch’s wiring into the harness. Looking for dark/cooked wire casings, exposed wiring, deformed plastic connector from heat, etc.


2004 Ducati ST4s ABS “Senna”
2002 Yamaha FZ1
1998 Ducati ST2 apocalypse edition
 

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I had exactly this issue happen 3 times. In two different years. And one day while the bike was apart on the bench for maintenance it happened again. Turns out it was the yellow relay by the left side of the headlight, the main relay. It`s what`s called a dual 87 output relay. Most relays have one contact that it NC and another that is NO. This one had none that are NC and two that are NO. One of the output contacts was burnt. I could physically see the contact close when I applied power but my meter was telling me there was no current path. Changed it and all has been good for a year and a half now.
 

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Same thing was happening on ST4. Figured it was electrical. Replaced the two relays and the 3 fuses under the seat. No more problems, of course I did this after pulling all the plastic and checked all the connections on the bike.
 

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Discussion Starter #8
Thanks for all the replies and suggestions. Sounds like I'll be tearing down instead of riding :frown2:

Recent maintenance history?
Bought the bike in '12 with 20k on the clock. Had full service done in '13, including new fuel filter and fork oil.

I do oil/filter, fluid flush, plugs, and K&N filter clean annually, but haven't had the plastics off to change plugs this summer. Typically have belts/valves, TB sync, TPS reset, etc. done every two years at a local shop.

It's more or less due for belts, valves, coolant flush and new fuel filter. Almost 40k on the clock now.

Been problem free to date and running great so far this summer. Aside from wheel swap, new rear caliper and bleed, I haven't done anything to upset it.
 

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I had exactly this issue happen 3 times. In two different years. And one day while the bike was apart on the bench for maintenance it happened again. Turns out it was the yellow relay by the left side of the headlight, the main relay. It`s what`s called a dual 87 output relay. Most relays have one contact that it NC and another that is NO. This one had none that are NC and two that are NO. One of the output contacts was burnt. I could physically see the contact close when I applied power but my meter was telling me there was no current path. Changed it and all has been good for a year and a half now.
That was what fixed my intermittent stalling problem as well.

Good luck, please let us know what fixes it.
 

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Discussion Starter #10
Thanks for all the input.

I took the plastics off and gave it a good look over, but found nothing obvious. I put in new plugs and cleaned/oiled the K&N while I was in there. Everything was pretty clean.

Fired it up a few times and had no issues, so hard to troubleshoot.

Anyone have a goos source for quality replacement relays? These are all stock and have lasted well. I'd hate to replace them with cheap stuff that may fail prematurely.

Thanks!
 

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Thanks for all the input.

I took the plastics off and gave it a good look over, but found nothing obvious. I put in new plugs and cleaned/oiled the K&N while I was in there. Everything was pretty clean.

Fired it up a few times and had no issues, so hard to troubleshoot.

Anyone have a goos source for quality replacement relays? These are all stock and have lasted well. I'd hate to replace them with cheap stuff that may fail prematurely.

Thanks!
This post answers most of your relay question: https://www.ducati.ms/forums/40-sport-touring/716583-st4s-won-t-start-again.html#post6928893

With those part numbers, Autozone among most other car parts places, will find equivalents.

While relays are likely the most common problem, you might also consider the crank angle/position sensor which gave me fits last year. I put up a thread showing the whole description of the problem and process in finding it, but the "winning" post is here: https://www.ducati.ms/forums/40-sport-touring/682322-rides-hell-michigan-spooked-my-motor-3.html#post6608970
 

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Discussion Starter #12
It took a bit of time to get back to it, get parts, etc. but wanted to update.

Fortunately, the bike failed a few more times while in the garage. It was obvious that the fuel pump relay was not buzzing like normal at key-on, so I replaced it (both actually) with new and everything seems good.

Thanks much for all the help and pointers. I almost forgot how much fun this bike is!
 

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It took a bit of time to get back to it, get parts, etc. but wanted to update.

Fortunately, the bike failed a few more times while in the garage. It was obvious that the fuel pump relay was not buzzing like normal at key-on, so I replaced it (both actually) with new and everything seems good.

Thanks much for all the help and pointers. I almost forgot how much fun this bike is!
I was typing while you posted this. As you'd described the failure I was suggesting a failed relay. I posted, then saw your update, then deleted and retyped my post. Glad you got around to getting yourself back on the road!

THUNDER!!!!!
 
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