Just dies on me

[woodardtt]

Long explanation...
my '05 just dies.
When I first got it one of the previous owners had installed a lotta electronic junk on it, including a keyless ignition/alarm. I stripped all that out and suddenly it would run. I'm assuming the keyless system bypassed some of the stock wiring. I couldn't find any cut wiring, but did identify a black/white wire jumping into the test connector under the seat. By applying power there the bike ran again! So I cut that into the tail light wiring to get power there when the ignition was turned on. Fine, everything worked, the ignition switch turned it on and off.
It ran like that for a year or so and then started to die randomly, but it would restart and run fine. That got progressively worse and eventually it wouldn't restart. I had used a "suitcase" connector to the tail light wiring and though that might be bad, so took that out soldered the wires and it worked again. But it eventually started dying finally died again and wouldn't restart.
I saw an article talking about resoldering a circuit board on the main power relays, but that really didn't seem to apply to the ST1300.
So I got a used ECM off eBay and tried that; it worked! It started right up and seemed to run great.
I took it out for a shakedown and got maybe 5 miles down the road begore it died again. It restarted, but immediately died again. While waiting for the tow truck I tried it and it started and ran long enough to position it for the tow truck and ran again long enough to drive it up on the truck. When we got it home and off the truck it started and ran long enough to get it into the garage.
I saw something about the fuel pump, but I can hear it chattering when I turn the key on and it seems to die suddenly (like an electrical problem, rather that sputtering out like a fuel problem), so I'm hesitant to start mucking around with with that.
What should I try now?
What do I look for now???

 

[Gus1300]

but I can hear it chattering when I turn the key on and it seems to die suddenly

You'll hear the pump initially as it pressurizes the rails when you first turn on the ignition/engine cut off switches. It stops until the bike starts but if it sounds weird, the fuel pump is probably your first place to verify. A fuel pump problem will result in a sudden stop as the injectors lose pressure, not a sputtering stop a carb system would have. And it shouldn't 'chatter' or at least I wouldn't describe the normal sound it makes as that.

Also weird that there was a jumper into the test connector; normally that's only when diagnosing the FI system for faults/clearing/etc. Strange that 'applying power' to that wire did anything so that might also be worth tracking down where it goes to/what it does that would cause that behavior.

I'm sure others will reply with additional info but it sounds to me like it's a fuel pump problem at the moment. If it starts at all, usually the ignition system and all of the associated safety relays are good to get it to that point.