Fuel pump issue puzzler-need collective wisdom!

[rthump]

I have a 2007 Hexhead RT that chugs and stalls when fuel in tank reaches about 1/3 full. Has happened 3 times now, and always at the same fuel level mark. Refilling the tank seems to make it go away.
I've already replaced the FPC with the new black powder coated one, and checked venting lines, added Heet to the tank in the event there was water, ran Techron through about 1000 miles before problem surfaced, ran GS911 diagnostics (no fault codes), inspected plugs, and since I was at it, gave the bike a TB sync, valve adjust, and reset on stepper motors.
One other important thing-the fuel pump was replaced by dealer 13 months ago under the leaky flange recall.

My hunch, and I'm not a mechanic, just read a lot on here, is that the fuel pump or in tank hose is somehow fuel level dependent and I am about to pull the pump. Would a crack or pinhole in that plastic yellow flex line somehow draw air instead of fuel when it goes from being submerged in fuel to being in the air?

I have an appointment to bring it to dealer next week, but I think since BMW bought the last fuel pump I may be stuck with paying for this one, so I am appealing to the experience of others for tips on removing and diagnosing the fuel pump for a possible fix.

 

[dbrick]

I have no experience with this symptom on my '07 R.

That the bike runs well when it runs suggests the pump itself is OK. I agree that it-only-runs-at ≥ 2/3 full suggests something awry in venting (is there a "whoosh" of air when the gas cap is opened?) or in one of the tank's internal hoses.

Did the dealer replace the internal hoses when the pump was R&R'd?

 

[rthump]

I have no experience with this symptom on my '07 R.

That the bike runs well when it runs suggests the pump itself is OK. I agree that it-only-runs-at ≥ 2/3 full suggests something awry in venting (is there a "whoosh" of air when the gas cap is opened?) or in one of the tank's internal hoses.

Did the dealer replace the internal hoses when the pump was R&R'd?

No vacuum detected when tank gets down to 1/3 full. Bike coughs and sputters and dies below 1/3 tank. Even after I have opened the filler cap and swished around to determine thers a couple of gallons in there.

Dealer replaced entire fuel pump assembly in May 2015 because the flange was cracked and leaking. Are you thinking maybe that they re-purposed the old in-tank fuel line? If that line is compromised, and since it is on the downstream side of the pump (fuel pushed through line instead of suctioned), would a crack make any difference? I mean, would having a cracked pressurized line submerged in fuel behave any different than one exposed to air?)

 

[dbrick]

On reflection, I don't think an in-the-tank fuel line crack downstream of the pump would cause this behavior, as the actual output to the fuel distributor wouldn't seem to be much different depending on whether the line was submerged or not. Testing the fuel pressure with the tank both full and then half-full would answer the question.

OTOH, they were in there, and fiddled with things. I suppose it's also possible that the new pump itself is defective in some way.

Let us know what you discover!

 

[rocketmanli]

Is it possible that the fuel level strip needs replacing, and that when you think you have the tank 1/3 full, its actually almost empty? That might account for the sputtering, and it going away after you fill it up.

 

[Texpaul]

I had an old K bike that displayed similar symptoms once. Took me forever to figure the problem out. Seems that I had gotten some bad gas at one stop on a trip. Bike ran fine after a fuel up but once the level got below a certain point the bike would cough, miss and only run on a couple of cylinders.
Turns out that the bad gas I got contained a bunch of stuff that looked like cat hair. Seems that water will collect on top of the gas in the storage tanks and that water grows a type of organism that can clog screens, filters and injectors. If the station pump has no filter, not that uncommon, this stuff (that looks like cat hair) can get pumped into your tank. As long as the tank has sufficient fuel all this stuff will remain in suspension but once the level drops enough to concentrate it it clogs the fuel screen and cuts of the fuel flow.
It wasn't until I removed the fuel pump and the tank and drained all the gas that I found this cat hair like stuff in the very bottom corner of the tank.
Might be something to consider.

 

[rthump]

I eliminated the false fuel strip reading by verifying the amount of gas it took to fill the tank after it sputters and dies. It was just under 4 gallons to fill, so I do not think the fuel strip is my culprit.

The cat hair theory is interesting and seems possible as this happened immediately following a long trip out west where I was gassing up twice daily from some pretty lonely looking stations.

I am now removing right side plastic to pull the entire fuel tank to drain and inspect. Perhaps the debris is stuck in there somewhere.

 

[rthump]

Solved! I hope!!

Thanks for the cat hair theory San Antonio! I pullled the fuel pump and inspected it. IT checked out fine and had some small fibers on fuel filter sock. Not bad.
Then I sip[honed out every drop of gas through the fuel pump opening, and shined a light down on a lot of grit and fibers in the deepest part of the tank, right where the fuel suction pickup is. I was able to wipe out the bottom with a clean rag as my whole hand fit in there. (I just hung the fuel pump assembly by the handlebar and did not disconnect any tubes or wires).
After cleaning it, I reassembled, added about a half gallon of fuel (straining it through a paint strainer funnel) and Voila! It started and idled just like always!
Even took her for a spin around a few blocks with so little gas and it works fine so far.

I'll add a bit more gas and go for a longer ride. I sure hope this did the trick!

 

[temesvar]

Thanks for the cat hair theory San Antonio!

I'll add a bit more gas and go for a longer ride. I sure hope this did the trick!

Good to hear that! We all are happy for you, and thanks for sharing it with us.