'99 ST2 with 40k miles on the clock. Service is up to date, but coming up on belts/valves, coolant flush and fuel filter.

Been running great all summer and I haven't molested it this season to give it reason to misbehave.

I was 7 miles and 15-20 minutes into my ride when it faltered for a second on a flat straight stretch at 45mph. Kept the throttle steady and it came back for 2 seconds, then simply died. Oil pressure light then lit as I was coasting as you would expect with the key on.

Once on the shoulder, I keyed off, keyed on and hit the starter. It fired right up, but died. Keyed off, took off my helmet and ear plugs, inspected for anything obvious. I waited a minute or two then keyed on again --dash lit and fuel pump whirred, as expected and fired right up again and idled fine.

I headed back home and added a few loops around the house for 30 minutes/15 miles or so. No issues at all --ran fine, idled fine and started up again in the driveway. Tank was 3/4 full with fresh fuel. I've had no other issues with it to date.

Any suggestions or thoughts from afar as best place to start?

TIA

It sounds like a fuel issue. Did you open the cap by any chance?

Quote from: ducpainter on September 16, 2018, 10:43:28 AM
It sounds like a fuel issue. Did you open the cap by any chance?

Thanks for the reply. Good call --I did pop the cap after the first failed start, but didn't notice anything unusual.

Are you thinking vapor lock?

I looked around in the tank with a flashlight, not knowing what to look for. Everything looked very clean and nothing jumped out as out of place.

I've peeled all the plastics and seat and am looking for any obvious signs of issues with wires, grounds, relays, etc. Figured I'd clean the air filter and replace plugs while I'm there. So far everything looks just fine...

No 'whooshing' sound as air entered the tank?

I was thinking a venting issue.

Gotcha. I didn't hear anything and didn't detect any extra pressure when opening the cap. I'll see if I can figure out how the venting works and check that.

Got the plastics off and couldn't find anything obvious. Changed plugs and cleaned/oiled the air filter while I was in there.

Not really sure what else to do besides wait for it to fail.   

Intermittent stalling problems are difficult because things test good when the bike is running.  First thing I would do is, with the bike running, turn the handlebars left and right.  Also gently jiggle the harness coming down the head tube. If the bike stalls you may have a broken wire in the harness.  Next I would suspect a bad main or fuel injection relay.  You could just replace them, they are cheap enough.  Problem is you will not know if you fixed the bike.  I would suggest you make a jumper wire to replace the relay.  If the bike stalls, remove the relay.  Jump between 30 (red) and 87 on each and see if the bike now starts.  If so replace the relay.  You need to work quick.  Actually, before that, turn the key on.  The relays should click and the fuel pump should run.  Does the relay click mean it is working?  no.  But no click means it is not.

I had a similar issue on a customer ST.
Flaky relay was not allowing full electrical power to the fuel pump, bike would run but fuel pressure was low, so running poorly.
First 'partial' relay failure I've found.

Thanks, guys. I appreciate all the input.

So far, all tests have been fine --I hear the usual clicks and whirs at key-on and it fires right up.  I'll try the handlebar turn and harness test this evening when I'm back home.

Is there a good source for quality relays?  Last relay I bought was from NAPA and was made in China. Don't know if that's good or bad...

Not sure if they have one, but they would know:
https://easternbeaver.com/Main/Elec__Products/Relays/relays.html

Other sources around, drawing a blank at the moment.

So I solved the issue temporarily with a '13 Multistrada 

But I missed the ST2, oddly. Got a new battery and cleaned up a few items. Bike fired right up and idled perfectly after a year of sitting in the garage.  After warmup I got a couple blocks before the engine cut out (straight line, no corners/curves). No sputtering. Lights, dash, etc. still powered up.

I coasted to the curb, waited a minute and hit the starter. Bike cranked fine, but no start. Tried a couple more starts and fired up on the third attempt. Got some fresh gas and rode around town for a good 30 minutes with no issues whatsoever, and bike actually ran great and still pulled well across the range.

I have a feeling it will do the exact same next time. Any more clues from these symptoms, or still thinking relays?

Now I'm thinking maybe contaminated fuel.

Quote from: howie on August 17, 2019, 10:12:16 AM
Now I'm thinking maybe contaminated fuel.

Hmm. Thing is, on both occasions, once it started it ran just fine after --all the way back home last time, and for the 2 miles to the gas station this time. I would expect bad cause to cause rough idle and overall poor running, no?

I'll do some more around-town rides this weekend and see what shakes out. Just don't want to end up stranded...

Bad crank trigger can do this sort of thing as well, though usually it won't run poorly.
It will run fine/start fine, or not, no in-between.

Quote from: Speeddog on August 17, 2019, 11:53:02 AM
Bad crank trigger can do this sort of thing as well, though usually it won't run poorly.
It will run fine/start fine, or not, no in-between.

I Googled 'crank trigger' and didn't come up with much. Can you please shed some light?

I did get out for a short ride Sunday. Bike started and idled fine in the driveway, then just died -no sputter or warning during the warmup. Usual crank and no-start for a few rounds. Gave it some gas, but still not start. Did smell very gassy, though. After about the 4th attempt it fired up like normal and ran perfect. Rode around town for quite a bit and no issues whatsoever.

It seems consistent in that at some point early on it will die, take a few attempts to start and then run absolutely perfect from that point on.

I did add some Seafoam at the first fill-up since it had been sitting for a year. Always fill it with super at usually the same two Shell stations.

Not really sure where to start...

OK, I didn't catch on that there was a ~1 year gap in this saga.

Did you replace the relays?

did you wiggle the wiring harness as Howie suggested?

After it dies and won't restart, do you hear the fuel pump priming at key-on?