2004 Idles rough and dies off throttle (Intermittent) pop similar to lean condition

[bplandis]

2004 ST1300 that has not had any recent work that may have caused my issue. The bike has high miles but has been well maintained. I dont run any additives of any sort. Stock bike mechanically.

My purpose of this post is to try to get a starting point to help with diagnosing an intermittent issue I am having. Any tests or scenarios I can put bike through/in, or notes I can take next time it happens to help narrow the issue?

Over the last few weeks the bike has developed an intermittent issue. Rode it yesterday 125 miles and zero issue. Bike overall runs fine, starts fine, idles fine. I do have idle up around 1300 (warm) which is a little higher than normal/manual but helps with my riding style. Has not happened enough that I can pinpoint the exact cause, but seems to be after low speed cruising or going slow (parks/in traffic). I can not remember it happing on an off ramp or at a stop sign after cruising 35 mph or more.

The issue is off throttle the bike will stumble and act similar to a carburated bike when it loads up. Acts like its "missing" and wants to run just stumbling/missing. If you pull the clutch in and blip the throttle a couple times it clears up and runs fine. If you dont it will die. Starts right up after it dies. No extended crank, no fuel smell, no sputtering after it starts. Last couple times times it has happened I am still moving/coasting and I clutch it, and hit starter switch and continue on.

Sunday it stubmled, had been idiling in gear, low speed throttle trough a park. It started to die and when I pulled in clutch and reved it up it "popped". Just like lean condition on a carburated engine. That is a first.

Have been doing some reading here over last couple days to get an idea of what to note and where to start. Low battery voltage (key off and/or while cranking), Ignition switch, vacuum leak, dirty T, electrical short, angle sensor, ect. Several have had similar issues with various fixes.

I have not pulled the plugs or done any trouble shooting, I hope Saturday to spend some time on it. Thank you in advance for any help/guidance and hope you all are well.

 

[Fawlty]

Probably the 5 way T needs cleaning out or changing. Plenty of help on the way. Good luck.

 

[MidLife]

Could also consider starting with the simplest: a tank or two with a fuel injection system cleaner additive.

 

[DannoXYZ]

Probably the 5 way T needs cleaning out or changing. Plenty of help on the way. Good luck.

Easiest way to diagnose this is:

1. tap into MAP sensor vacuum line with T and measure vacuum at idle and at 3000rpm. kpa1=? kpa2=

2. measure MAP sensor output voltage idle and at 3000rpm. volts1=? volts2=?

Do #2 twice, at MAP sensor itself and at ECU connector. This gives you insight into data that’s arriving at ECU. You may even find corroded or broken terminals & wires if signal at MAP sensor is different than what arrives at ECU. You’ll be able to witness incorrect data as bike is stumbling. As with any computer, garbage IN = garbage out.

 

[Rob20111]

Inspect your plug caps very closely for damage, especial the rear 2 cylinders which can get damaged by the plastic valve covers.
You can cut off the extra unused loop in the cover to avoid damaging plug caps.
Any small cuts might cause a short to ground.
Check that the drain inside the rim of the gas cap is clear and not plugged with debris. A shot of compressed air to test.
If it’s plugged then water from rain or washing can’t drain to ground and may end up in your fuel.

 

[Igofar]

Your fuel pump is dying, or the hose has developed a pin hole leak.
You can hear it prime, thinking its working, then it bleeds off pressure and you start running out of fuel.
The reason it starts back up after you stop, is because your ECU re-primed it again.
Lean pop or backfire, is telling you "I'm not getting enough gas".

 

[bplandis]

Larry, Rob and crew will get to it. Have not had dedicated time to tear into it. I will report back as I dig in.

Thank you for the help and guidance.