Fuel pump whine

[jrbelknap]

Hi K-Experts,

I know this has been brought up before but I can't find a thread that specifically addresses this issue. New (to me) 1995 K1100LT with only 21K. When I bought it in Dec and rode it there was no noise, even after 20 miles on the freeway. I rode it home from the dealer the next day - a distance of over 100 miles. By the time I got home the reserve light came on and I could hear the fuel pump whining. I filled up the tank - and still have the whine. It seems to be developing pressure or vacuum in the tank - if I open the gas cap the whine stops, then slowly comes back after a few minutes idling with the cap closed. There are no hoses on the fuel tank vent tubes.

Only thing I noticed is the fuel pump assy is slightly loose, ie. I can pull the whole assy' with mount and vibration damper, out of the well that it sits in - is this right or should it be a tight fit? Any other thoughts?

Thanks,

John

[lostboy]

There are two tabs in the pump mount which should lock the pump into the tank. Push down on the nylon mount until you feel them snap into place.

[jrbelknap]

Ok, I'll try that again - tried it once and it didn't seem to do anything.

Thanks.

[58058D]

The vacume is likely due to a clogged vent line, no tubes? Were they just removed and the nipples left bare? Could be one is plugged. Needs to be rectified or you may have issues with fuel delivery and/or deformation of the tank.

[chilibowlfan]

Oh gosh! Do not pass go, do not collect $200, replace the fuel filter now!

[98lee]

Hi K-Experts,

It seems to be developing pressure or vacuum in the tank - if I open the gas cap the whine stops, then slowly comes back after a few minutes idling with the cap closed. There are no hoses on the fuel tank vent tubes.

John


The K1100 uses the "air accumulator" cup on the frame below the tank vent tubes to catch any overflow and route it to the ground by the rear master cylinder.

If you are getting a vacuum build up in your tank, the problem is a blocked vent tube. The front one is the tank vent. The rear one is the rain drain for the filler ring.

If you have a Mity-Vac, try sucking on the tank vent. It might suck out what is blocking it.

Another way to clear it is to blow compressed air through the vent tube (with the filler cap open). The disadvantage to this method is it will blow what ever is blocking the vent into the tank. Might not be a huge issue but something to be aware of.



:dance:dance:dance

[jrbelknap]

Thanks guys. I got the pump assy seated into the well and will work on clearing the vents tomorrow (Sat). Appreciate the advice.

[gsmetal]

Tell your fuel pump to quit whining and get to work. :thumb

[jrbelknap]

Ok, I blew through the vent lines and replaced the fuel filter. The whine still starts up after about a minute of operation and gradually gets louder, settling in at a steady high-pitched whine - loud enough for other people to notice it at stoplights.. Fuel level doesn't make a difference and neither does fuel cap open or closed. I think the fuel pump is failing. The dealer installed a new pump before I bought the bike (only 300 miles ago) but did not change out the filter - when I removed it you could barely blow through it so I wonder if it was plugged up and caused the new pump to go bad.

[Gilly]

If the bike ran fine when drove it home, I would say there is something "wrong" about a blow-through test, but not sure why that wouldn't be a valid test of the filter. The bike is pretty sensitive to the filter and I'm sure it would start stumbling way before it would be hard to blow through the filter.
I am wondering if it might be the rubber damper or the position of the pump in the damper (too low and pump is rubbing on the tank bottom).
Gilly

[98lee]

Fuel level doesn't make a difference and neither does fuel cap open or closed.


It seems to be developing pressure or vacuum in the tank - if I open the gas cap the whine stops, then slowly comes back after a few minutes idling with the cap closed.




????? Which is it?





:dance:dance:dance

[jrbelknap]

Well, it's what I posted most recently but first in your reply post - it doesn't matter if the cap is open or closed. When I first was trying to figure it out I would hear the sound, shut off the bike, use the key to open the filler cap and the noise would have stopped. I assumed it had to do with tank pressure or vacuum, ie. bad venting.

Now I have gone to diagnosing it with the cap open and realize the noise still starts back up after about a minute - even with the cap open. A gradually increasing high-pitched whine. What is interesting is that the noise stops upon shut off and takes a minute or so to start back up again with the engine running.

Really weird.

[lostboy]

I've heard these pumps do this from time to time. I'd either replace it or carry a spare.

[jrbelknap]

Oh I'll replace it that's for sure - darn thing is so loud it's embarrassing. :blush

[Gilly]

If you don't mind sticking your hand in the fuel, once it gets loud, just try moving the pump side/side or up/down to see if the noise changes. Could be a bad rubber isolator, or again, as i mentioned, the pump might be set in the isolator wrong and the pump could be rubbing the inside of the tank.
Gilly

[jrbelknap]

Thanks Gilly. Already done it once but not with it running - that's how I found the pump wasn't seated properly. Unfortunately seating it didn't help. I will try it again running this time - I've poked and prodded to no avail but maybe getting a hand on it will be more useful.

I'm also planning to replace all the in-tank fuel line this weekend in case it's leaking up near the top of the tank and sucking air. I noticed when I replaced the fuel filter that the short little hose had gotten hard and had micro cracks in the surface. Appreciate your ideas.

[jrbelknap]

Well I brought the bike back to the dealer. They put in another pump - still had the sound. They asked to keep the bike, gave me a loaner and ordered a new vibration damper/mount thing. When they installed that the bike still made the sound so they put in another replacement pump (3rd in total). Problem solved. Two bad pumps.

The bike runs great again - feels smoother than before so it may have been running lean. Man was it nice to get it back! My hat is off to BMW of Santa Cruz County for persevering on this issue on a 15 year old bike they sold me used. No questions asked, a loaner bike while they had mine, and a great attitude. I know where I'm buying my next bike.