Fuel Tank Pressure Build-up

Ha ha.... Beer with a German... I see an iceberg ahead....... Yes there is a need for the T... well...at least a vent...not from the tank. You see if the only vent into the CC was through the tank....when the purge valve would open and suck in the fumes, it would cause the engine to run too lean..... so they put a vent line down in front of the rear tire.... wonderful.....now the motor is breathing in a mix of tank fumes.....and fresh air...when the purge valve opens. Awesome.... But when the Germans tested this.... they did so i Denmark, where the weather is always sunny 360 days of the year...... Ha ha Joke.... but seriously....no rain....because when it was driven in the rain, and the purge valve opened.....fresh air from the vent in front of the tire was sucked in rather than the over pressurized tank ( remember the tank has to produce about 4-5 psi to vent.... In rain.......perhaps...cold weather....that is not likely to happen....therefore.....the little tube in front of the tire now is a vacuum cleaner.... whater is now sucked up....and into the intake manifold...and combusted.... well...trying to combust.... result....Stalling. Solution...either take out the one way check valve, and risk offending the Bavarian engineer who created the system...... or simply put a T so it now will suck from under the seat.....well ....we know the results. Reason for the hose going down..... You have all these people who want to maximize the endurance....and tip top off the tank....on the side stand...... Awesome.....but the fuel has to go somewhere....and gravity rules.....fuel with expansion now enters the CC...( Charcoal Canister)....and drips down in front of the tire.....Nice. The short and great fix would simply have been to remove the Check valve..... along with installing the T.....so fuel can still drain down.....and when driven in water.....the under the seat hose vents, when water enters the down pipe. OR.....Simply leave it like the Bavarian's did for them self... ( smart people)... simply don't install the CC.... Ha ha.... they are still laughing at us Yanks..... or in this case Danes......ehhh...uhmmmm... living in the US.

My bike stalled on two recent trips...symptoms are easy....riding in over 28 C for hours, gas is about 1/2 full and bike dies mid stream. Down shift bikes comes a live but then dies...can't get into high gears without stalling so i cruise at lower speeds and lower gears. bike finally gives up..pull over. Turn key off and wait. At first I did not pop the tank lid and the bike would start and go for a few hours. After awhile I did pop the lid when the stalling began..after riding for hours in extreme heat...seemed to work.

Bike into the shop...they can not find a fault code and replicate the problem...I told them they would not be able to replicate the problem unless they were riding in the same conditions with the tank not full. Said they checked all the hoses etc...everything in working order. Nothing was done. So, I will pick up my bike tomorrow and because the temps are cooling down here I am certain there will be no issues until next time we ride in crazy 90-100 degree heat.

So ... when you popped the tank lid did it release PRESSURE or was there a VACUUM?
Sometimes it's hard to tell....

If a vacuum, then I would say your charcoal canister is plugged or a related hose has a kink in it or your check valve is bad...
and ... (AFAIK) the bike is not equipped with instrumentation to detect that fault and record it to the computer logs...

If pressure ... well then I've got no clue .........:huh

I carry a little "straw" from a can of WD-40 in my tool bag so that if I ever get the problem I can close the tank lid with the straw inserted and keep the tank from moving away from 1-atmosphere of pressure ... have not had to use it yet...

there was a pop once...but really not that mush sound. They said they checked out everything...I will find out more tomorrow.

Thanks!
Keep us posted.

Based partly on this thread http://www.advrider.com/forums/showthread.php?t=500968 I think the valve on the fuel tank is a 2 way valve. It allows air in to deal with vacuum in the tank via the canister and allows pressure out also via the canister (tube that goes to the throttle body).

If some one wants to test that theory, take the hose off at the tank that goes to the canister and see if you can suck air in and blow it out. My guess is it only works in one direction, or at least easier to suck than blow.
I suspect the breather valve in Yeti's diagram is an on demand switch that controls when the fumes in the canister are drawn into the throttle body.

I know it takes pressure to over come the tank valve to allow fumes out. I have heard someplace it is 4.5lb.

Even if you remove the charcoal canister you will still get the build up of pressure in the tank until you trip the pressure release valve at the tank. That is how mine works. BTW if you do remove the canister do not cap the hose to the tank.

Yeah Gary ... it is my understanding as well that the valve on the throttle-body side is an electric solenoid valve controlled by the computer.

Plenty of things like this: http://www.ascycles.com/detail.aspx?ID=71245 to help deal with pressure on the negative side, but are there two way valves which allow the valve to be tripped at a set (albeit low) pressure level, bi-directionally?

Prefer to not vent to atmo, and I do find myself going from sea level to 7200' on a weekly basis, including some 30+ degree temperature changes.

one can blow it the tank with the vent line removed but you get a very very small flow with a vacuum. (a check valve). From what i understand there is a "stone type" vent on the pressure relief. I used to have high pressure also when I opened my tank... not anymore....

see my drawing.... I have the flow arrow drawn in reverse)

I thought it was a ball and spring, not a stone.I thought that was what I said, did not notice which way the arrow was. It is the only line so it must do both, obviously not with the same amount of pressure required.

It has to go through the canister both ways. When I said verify, I meant the ability to draw vacuum in through the canister and difficulty in blowing it out through the canister. When this valve on the line from canister to throttle body opens, engine vacuum could not only evacuate the canister but assist in opening the valve in the tank. How hard did you suck on the tank line?

My tank line is disconnected with a filter on line end. It still builds up pressure occasionally on hot days.

I guess I could pull the valve out and check exactly how it works, but it has been that way for 3 years with no harm. It would be different on a carb'd bike.

Note that there are 2 check valves back at the R corner of the tank under the trim panel.

#1 is the large white unit bolted into the tank where the vent hose attaches. That is the weighted tip-over shutoff valve that you can hear knocking around when you rock the bike back and forth.

#2 is the inline check valve with the 2 way properties being discussed. It is a 1" long silver cylinder stuck inline to the vent hose about 6-8" behind #1. It is ziptied to the frame before the hose does the 180 and heads back down toward the canister.

Inside that little cylinder is a green ceramic check ball. It is porous, with microscopic holes in it.

Those pores get plugged up with the aluminum corrosion dust from inside the cylinder and cause your tank to hold pressure beyond the 5psi expected.

Solution? The cylinder splits into 2 pieces. Open it, toss the check ball in the trash, and reassemble.

Mine has been like this all HOT summer with no ill effects. Canister still attached and working fine.

This permanently cures tank POSITIVE pressure, and lets you keep the canister to control the fumes in your attached garage.

The mighty Joel W. helped me with this diagnosis - - I'm just putting this info out there for the masses. He said BOTH valves can stick, so check them independently (suck/blow through them - it tastes like shit, so be prepared.) He did say that #2 is the usual culprit.

Thank you, I feel exonerated and informed at the same time. Good info, should be in a sticky.

There seems to have been a plug in some line that caused the fuel pump to heat up and cause the pressure. At least that is what I am guessing from the fault code report. It shows good voltage put very low (almost zero PSI) fuel pressure from the fuel pump.

READ OUT BELOW FROM MY GS911

10168: Electric Fuel Pump System faulty
The fault is not present now.
This fault occured 4 times.
Logistic counter: 31
Symptom: No signal or value.
MIL set: No

Fault code history:

Electric Fuel Pump Voltage 12.62 V 12.25 V 12.62 V

Odometer 15952.6 miles 15952.6 miles 15957.6 miles

Engine Speed 3280.00 rpm 1160.00 rpm 1360.00 rpm

Measured Fuel Pressure 0.39 hPa 0.41 hPa 0.37 hPa

Throttle Valve Angle 29.30% 0.00% 0.00%


If you like to work on your own bike like me then this tool (GS911) is invaluable. The reports it provides look much better then this but I was not able to transfer it directly via text.

Does anyone else have the same or different interpretation of what caused this as I do?

Original symptoms: Bike stalled from a standstill or very slow movement; It would restart but got progressively worse until it would not; and finally after it would not restart I opened the gas lid and fuel came out like a guesser (a liter or more).

Any insights would be welcomed.

andy

Andy:

I'm not sure how I would interpret that ....

For example -- lets say the impeller wheel were spinning on the shaft of the fuel pump motor, or the bearings in the motor were going bad causing it to run slowly .... or say the input filter sock were clogged ....
would the reported fault not still be the same ...

i.e. good voltage to pump, but pump output was crap?

I'm just brainstorming with you here

Andy, did you ever figure this out?

I've been having the same symptoms on my HP2. Intermittent stalling and same error code on the GS911. My guess is a clogged fuel line upstream of the pump, probably due to debris in the tank or bad gas.

I'm about to take apart my fuel system and check, but I'm wondering how this turned out for you.


EDIT: yep, turns out I had a large wad of black gooey glop (technical term) backing up the screen of my pre-pump filter. I hope your problem was similarly easy to fix.

Mine was also the little porous ball that got gummed up and thus creating a blockage. Have not had the problem since. Gas in the Phoenix area just seems bad, all of my bikes carbs (harley, and a couple of honda dirt bikes) get gummed up. I am now using sea foam and it helps.

Thank you. Your description helped, that fuel tank check valve must have been part of the reason for my stalling out, I blew it out, was full of aluminum dust, I presume, the valve wasn't passing any air. Had to take off the rear panel to remove.

I also changed the spark plugs, which also may have helped. Since I recently filled up at a totally unknown gas station in a shady part of town, and we have had about 150mm of rain the last week, so I also drained the gas and filled with new Chevron gas.

Also used never-seize on the threads, and some electrical conductivity paste on the sparkplug/coil interface part of the sparkplug. I am quite surprised of the rust on just one of the spark plugs, it's totally orange and crumbly.

There was so much crusties down there in sparkplug land, I walked to Canadian Tire and back to purchase a compressor and jet spray gun. Also another 5 Litre jerry can. Just a 2 gallon 1/2 horse compressor (light enough to carry) makes enough pressure to blow the shit out of the sparkplug hole. I also used it to blow out the fuel tank check valve.

Guess I have to say that plenty of folks have been more than ample with their time in describing issues. I've been a big reader and even though it's been a few years since my early wrenching days I'm feeling more than relieved that this problem has been fixed. It idles so well now, super sweet acceleration and just a pleasant beast again. I don't mind taking some extra time to express my thanks to all the anonymous (to me, a recluse) folk out there taking the time to take pictures and notes.

Oh yeah, but I must have put it all back together with a couple fewer screws. I gotta hand it to those BMW designers, the thing goes back together solid, not like some bikes. Challenge is in finding the right length bolts/screws. I got to the final piece over the top and I am out of long 25tx! No worries...

BTW the title of this thread should really be 'Excess fuel tank vacuum fail (solved)"