Fuel pump runs on at startup

New ST owner here and I haven't yet taken anything apart to see what may be going on - too much fun just riding this beast... (2005, with just 18,000 miles on it!) I'm posing this question to get the starting point for my investigation...,

Here's the symptom so far: Fuel pump runs on longer than I'd expect and doesn't stop abruptly at start-up AND starting is harder than I'd expect UNLESS I open the throttle a little while I'm cranking it. (I don't like to do that because I think it's probably loading the bearings more than necessary before the oil has circulated.) Once started it runs great; no missing, no stumbles, no stalling, lots of power, no black exhaust.

No gas leaking out of the system (I'd smell it.) I haven't looked at the plugs yet to see if any are wet. I haven't run a full tank of gas yet to see what the fuel mileage is.

I'm suspecting an injector that can't hold pressure and that's where I'm likely to start looking unless the seasoned advice of this message board suggests another path. What do you think?

Thanks,

Jack

Key On - the fuel pump on my bike runs about 2.5 to 3 seconds before it cuts off. A low battery might lengthen this time and or create slower starting. If as you say everything else seems to be good after it starts and the bike runs fine.....just ride the bike. Not a tank of fuel run thru it yet - that's less than 300 miles. Give it a little time before tearing into a problem yet to be created.

jjoyce2 said:

I'm suspecting an injector that can't hold pressure and that's where I'm likely to start looking unless the seasoned advice of this message board suggests another path.

Click to expand...

There's no sensor to tell the ECM that the fuel rails have reached operating pressure, which leads me to believe that the run when the ignition is turned on is timed. As Dave points out, the the pump should run a few seconds when the ignition and engine stop switch are both turned on and then continuously when the engine is running.

Your bike hasn't seen much use, and I'd chalk this up to your fuel system getting gloppy before digging into anything else. Run your next few tanks with a fuel system cleaner and see if the problem clears up before diving into anything else.

One other easy thing to check in the mean time is whether or not the fuel pump relay is sticking. Just swap out the fan motor relay temporarily and see if you get the abrupt shutoff you're looking for.

--Mark

Thanks for the perspectives and the advice.

I am inclined to let this sleeping dog lie until it's more of a problem, but I can't quite banish it from my mind. I'll probably just keep listening until it gets worse and run a shot of seafoam meanwhile, 'cause what can that hurt?.

FWIW, I can hear the pump almost stop running at the end of the prescribed time, but the mechanical groan changes in pitch and regularity for another 3 to five seconds before it stops.

Thanks again guys.

Jack

Sounds normal to me. The hard starting may be something else.

With that few miles the first thing I would do is run several tanks with SeaFoam in the fuel to help clean out any old fuel deposits in the fuel system.

Seafoam and a relay check - that's my immediate agenda.

If the startup sequence is timed rather than pressure related, the relay sounds a likely culprit.

I'll let ya know what I find, if anything.

Thanks all.

Jack

Well, this is embarrassing.

I guess I shouldn't be surprised that sounds are so much clearer when I'm not wearing a helmet.

So, I was swapping out the relay to see if there was a change in fuel pump behavior when I discovered I wasn't hearing the fuel pump running on after all. I could feel the relay clicking and heard the fuel pump stop, like clockwork.

The noise I misread as the fuel pump is a mystery to me now. It seems to be coming from the nose of the bike, in the fairing, maybe between the dash display and the headlights. The electric windshield is operating properly, and running it up and down, stopping at either end or anyplace along its run, nothing has an influence on the mystery sound. The sound continues unaffected and eventually stutters out.

Unless the horn is getting stray voltage and making some non-horn-like noises, I don't know what I'm hearing.

Any ideas?

Maybe the headlight motors?

Check for proper movement on the headlight adjuster. They should stay fixed wherever you leave the knob. Or maybe the horn... does it do its normal 'meep meep'.

Or just crawl around to the front of the bike as you turn it on. Horn is on the right side behind the plastic. You'll see two cutouts in the inner fairing that lrt the sound out.

The headlight motor system sometimes "hunts" slightly up and down making noises similar to your description. It only seems to do it at start up for a moment or two.

I had mine replaced under warranty in 2006. Now and again a thread comes up on this but mine that was replaced does it occasionally after all these years. I make a habit of running the headlight adjustment up and down every few rides if not every one. I think some corrosion may develop in the rotary dash switch or in the headlight motor what-have-you. This [turning the adjustment knob from full deflection to full deflection] seems to minimize the times it happens and how long it does it.

https://www.st-owners.com/forums/showthread.php?15247-Unidentified-Noise-in-Dash-Area&highlight=headlight+motor

https://www.st-owners.com/forums/showthread.php?104595-Buzzing-Under-the-Hood&highlight=headlight+motor

https://www.st-owners.com/forums/showthread.php?95817-New-noises&highlight=headlight+motor

jjoyce2 said:

The noise I misread as the fuel pump is a mystery to me now. It seems to be coming from the nose of the bike, in the fairing, maybe between the dash display and the headlights. The electric windshield is operating properly, and running it up and down, stopping at either end or anyplace along its run, nothing has an influence on the mystery sound. The sound continues unaffected and eventually stutters out.
Any ideas?

Click to expand...

+1 that does sound like the headlight adjuster hunting. Mine did it brand new. Exercising the knob cleared it up and it hasn't been a problem since. I haven't noticed any dead zone or dirty wiper behaviour since.

Jeez louise! I never had a bike with a headlight motor before!

That's what it was, the headlight motor hunting to a position up then down, then up and down - I could watch the light migrating on my garage wall.

I played with the knob some to no change, but later I'll run it to both ends to see if that minimizes the activity.

Thanks guys! Thank you, thank you, thank you!

Jack

Hopefully that clears it up.
If it comes to it. The green connector at the head light motor pull and check for crudded up contacts.
You should get continuity from ground to the green wire.
Battery voltage from ground to the black/brown wire (key on).
A smooth varying voltage (key on) from a ground to light green center wire 1.2 to 10.8 volts as you rotate the adjustment knob from end to end.

Just a wag, If it smoothly moves to an end point then hops or jerks it's probably trying to move past a physical stop. Crud or a failed contact crimp on the center wire might put less than 1.2 volts on it. If it never stops moving you might want to just leave it disconnected until you get it squared away. You could just key off when it's close to where you want it disconnect it then use the manual adjustment to put it where you want it aimed.