Altitude problem with F650GS twin
 

If the following rings any bells I would love to hear any suggestions:

It's the worst kind of problem ie intermittent... Basically the bike loses all power for a second or so and then picks up again exactly as if I let go of the throttle and then slammed it on again. It only happens at altitudes above 3000 metres and only after a solid hour or two of continuous riding. If I stop and turn the bike off for 10 minutes it usually goes away but sometimes not. At one point I thought it was the breather tube on the tank being blocked and so I pulled over when the problem was happening and opened the tank cap, thinking that if the breather was blocked, that would clear things up. One time this made no difference and the second time I tried it it killed the engine and I had a nervous few minutes in a desolate place here in the Peruvian Andes unable to start the engine :) I don't really understand why this would kill the engine but maybe the system is pressurised in a way I don't understand??

I have changed the spark plugs and looked at the injectors (look clean enough to me). I was wondering if it was dodgy fuel as can be common in the Andes but the last time it happened it was fuel from the coast and of a higher octane which is supposed to be much more reliable. At that point I cleaned the air filter but it didn't seem particularly dirty. It's possible that has fixed it as it hasn't happened since but I am dubious as the following day was just descent and I haven't been back up high since.

I will be heading to Bolivia which is all about altitude and lacking in much mechanical support soon and I would like to feel more confident that I won't get stranded somewhere.... I am in Lima for the next day or two which is the nearest thing to civilisation I will see for a while (although the BMW dealer here has not inspired my confidence by messing up a simple valve clearance check..) so here is the place to take any action...

Thanks for any suggestions!

Nearly four years ago and not quite the same problem, but stuttering and stammering at altitude...

Turned out to be the side stand switch.

Thanks Tim. I'll give the sidestand a wiggle next time it happens.

Guy

Fuel Pump
 

Guy,
My twin did the same & I thought it was bad fuel (I'm in Africa at the moment) but Chris at Jungle Junction said this "No i have not attended to the Fuel pump problem yet, thank you for the early notice.
We had several BMW F 650/800 Gs with the same symptoms and know wot to do." So may pay to check the fuel pump.
Thanks
Paul:thumbup1:

Thanks for that Paul. Any suggestions as to how I would go about checking the fuel pump?

It would make sense if the pump overheats after a hour or so of constant use and that this only matters when it is working against the low pressure at altitude. Or something like that...

Does it occur when the fuel level is low? - pump is cooled by fuel in the tank and some overheat when there is not enough fuel to cool efficiently.

You can test by checking output volume - exact figures can be found on advrider forums.

Possibly fuel pressure sensor also.

Thanks for those ideas Docsherlock. The problem usually occurs after at least an hour of riding - more often 4 or 5, so yes the tank is generally less than half full. Chris at Jungle Junction has kindly sent me some instructions for cleaning the fuel pump so I'm going to try that.

Twin
 

Well I guess you don't need his email then LOL
He really seems to know his bikes. Mine did the same tho after about 4 or 5 hrs just goes to cut out like you've run out of petrol & if you idle off a fair bit it kicks in and goes again, but a couple of times mine stopped completely & started again about 10/15 mins later.
Cheers
Paul
Oh yeh I really love the bike !!

Enfield
 

Guy,:offtopic:
I see you have an Enfield ! I just bought one in India about 2 mths ago & is sitting on the docks in Brisbane but I want get to ride it till Xmas when I get home. I think they are fantastic bikes !!!!!:thumbup1:
Paul

Yeah I loved my Enfield! Broke down a lot but sounded like a spitfire when i rode through those Himalayan canyons :funmeteryes:

As for the GS, this is the first genuine problem in 23,000 tough miles... Have the fuel pump out and have briefly run it backwards (in fuel) Hopefully that will have removed any crud.

Take it easy.

Guy

Hey Goo,

Check out this thread on advrider:

Fuel pump for 800gs - ADVrider

Good luck with it. Might be worth getting a GS911 tool.

Hi Docsherlock

Interesting thread - so are you suggesting I bypass the FPC?

I do in fact have a GS911. What are you suggesting I do with it? Bearing in mind I only have the mobile version with me.

Firstly, run some techron through the fuel system. Then:

1. Check to see if there are any error codes thrown. If there are, there is likely your problem.

2. Check your fuel pump output - if low, there is your problem.

3. IIRC the fuel pump controller has been less of a problem on the F798GS models; worth disconnecting the fuel pressure sensor to see if that fixes the problem.

Thanks for that! How do I check the pump output?

You will need to double check the exact procedure in the manual but I believe you need to check the outflow (?90 l/ph) and pressure (??50 psi) for which you will need a container and pressure monitor. I am not certain of those figures - need to cross reference to manual.

I'd take off the fuel pressure sensor first and see if that made a difference as supposedly the bike runs fine without it, albeit the pump is at max pressure all the time.

So yes, the GS911 shows fault code 10168 - electric fuel pump faulty (most likely: fuel pump electronics/driver) not present now

Real time values:

Fuel pressure: 4500 mBar dipping to 3000 occasionally.

As usual, after cooling down for 10 mins the bike runs fine. Looking at that heatsink on the FPC, I wonder if that isn't the most likely component to suffer from heat...?!

I couldn't find Techron but I put some STP gas treatment in the tank which looks to do a similar job.

So I will try disconnecting the fuel pressure sensor and see if that cures it.

Sorry to hear about your troubles Guy.

Doesn't surprise me though, you might remember that I advised you to take a spare controller and pump with you as the most likely pieces to fail on a long trip....

Lukas

No-one likes an "I told you so" Lukas...

And in my defence, various knowledgable sources including BMW themselves told me that the FPC issues were confined to the 1150/1200 bikes and did not affect the 800s...

So much for research

Hi Docsherlock

So I bypassed the Fuel Pump Controller and the problem remains. Do you think it would be reasonable to assume this means I have a faulty pump? I am on the point of getting a new one sent from Europe (thanks Lukas!) but it would be a long wait for nothing if the problem is elsewhere.

My GS911 showed the fuel pressure wobbling at times and somewhat in line with the faltering of the engine. I figure that bypassing the FPC rules out a problem with either the sensor or the controller, right?

I don't have the facilities to test the output volume etc. and anyway the conditions that cause the fault would be hard to replicate - atmospheric pressure and length of operation. It does seem to temporarily fix things if the tank is filled so that suggests it's a temperature-related issue in the pump.

Incidentally , I ruled out the sidestand as it happens with the bike in neutral.

Any further thoughts or shall I just go ahead and get a new pump?

Thanks for your time!

I should also mention that the removal of the FPC in the chain has made the problem worse which to me suggests the pump is at fault - in that now the pump is working harder at full pressure all the time.

I'm curious to know the exact function of the FPC? Does it provide a varying voltage to the pump and is this to maintain a constant fuel pressure? ie it makes up for pump inconsistencies? Or is it more complicated than that?

And any suggestions why altitude would cause this issue? Is the pump working harder to conteract the ambient oressure?

Bypassing the FPC doesn't really help distinguish the sensor/controller contribution.

Unplug the sensor from the end of the fuel rail and see if that helps.

However, it does seem that the problem is the pump itself given the history and GS911 reading.

How much extra is it to buy the FPC, pump and fuel pressure sensor as opposed to the pump alone? If you are having something sent from Europe you better be damned sure the diagnosis is spot on or you may have to wait for another component; for a couple hundred bucks I'd buy all three and get 'em sent at the same time and swap the whole lot out; if you can narrow it down when you get the components, then sell the good stuff or keep as spares as you will probably need 'em at some point anyway - it's a BMW:innocent:.

However, from what you have written, my money is on the pump itself as it can't run properly flat out (removing the controller makes problem worse, worse when hotter i.e. low fuel).

The FPC varies the pump output depending on various sensor inputs so it is not working flat out all the time; bypass it and the pump runs at max all the time.

I think the problem being worse at altitude is a combination of your hypothesis (working harder to maintain pressure) and the pump running hotter up there, if my basic physics serves me correctly.

Good luck with it.

DS

PS don't forget to mention this in future ads for your bike - karma is a bitch; but actually, in these bikes, having a new fuel pump is a good selling point at your mileage. That's karma for ya.

Thanks for all that! I tested the pressure sensor as described in my Haynes Manual and the impedances are correct. I then disconnected it and went for a spin and no change although I haven't been able to give it a long enough run to be totally sure yet. The person who is sending me the pump and controller may also be able to send me a sensor so I should be covered...