Weird engine cutting out problem

[FreiWild]

Since a couple of weeks I have experienced a strange problem with my BMW F800S, the engine kept dieing when I went to change gear, e.g. roll off the gas, pull clutch, shift, engine is off and I am coasting along.

There was no trouble restarting the engine while still coasting. It seemed to me that the engine RPM dropped off so far, when I pulled the clutch, that if I did not shift fast enough the engine would cut out because of this.

I've had the bike at the workshop, where they read out the fault codes and recalibrated the idle control. Thinking it was fixed I went and drove a couple hundred km home. When I came up to the end of a traffic jam, I went to pull the clutch, and the engine cut out in the same manner yet again.

The problem, only manifests itself after a prolonged time at top speed (was driving ~1.5 hours at or close to top speed beforehand). Funnily enough, after I switched the bike off by the side of the road and waited 3 minutes everything worked perfectly yet again.

Any ideas, as to what it could be? Will be in touch with the workshop in order to establish what they really did.

Thanks a lot in advance!

[Pothole]

if you google it there's lots of results. There was a safety recall on the GS and GT models for this very thing.

http://motorbikewriter.com/bmw-safety-recall-engin...

[boyse7en]

Exactly the same as my F800S. I think it's to do with the engine leaning out the mixture for high-speed running, then a sudden closure of the throttle cuts the fuelling and the engine dies.

I've had my bike 6 years now and haven't found a cure... If you find one, I'd love to know!

[FreiWild]

Thank you very much for your answers. I foolishly did not google the problem, should have done that beforehand really.

Anyway, it appears to indeed be a problem with the mixture, or the side stand switch, or the air intake, or a lack of software update... You can see where this is going.

Kind of get the urge to sell the bloody thing.

Anyways I've got a nice list of possible sources, so will go over these with the dealer. Still can't believe that BMW haven't found a proper solution yet.

[crofty1984]

Fifty quid. It's knackered mate innit?
Hope you get it sorted. Sounds like it shouldn't be too expensive if you can get it done under the recall.

[smack]

What you describe sounds like a Throttle Position Sensor type of problem. Does that bike have one?

[xpc316e]

If the sidestand switch is faulty, the rev counter will drop to zero when the misfire occurs (at least that was the case with my K1200RS).

[boyse7en]

I've not bothered to run through a list of possible solutions, as I guessed it could be an expensive method of trying to chase an intermittant problem.

I know it only happens after a high speed stint followed by a throttle-off stop (eg, motorway, followed by exit to a roundabout requiring a stop) so i just keep the revs up with the throttle when I pull the clutch in and use the back brake on the last bit of stopping so it doesn't stall. I don't even think about it now.

[podman]

My old EXUP did exactly this, it turned out to be the tank breather blocked, start with the simple stuff first mate, that lesson has been refreshed to me of recent with my "electrical fault".

[FreiWild]

Will certainly do more reaearch on this and try everything I can DIY first.

xpc316e said:

If the sidestand switch is faulty, the rev counter will drop to zero when the misfire occurs (at least that was the case with my K1200RS).

Rev counter does not do this, so can probably eliminate that from the list then, thanks!

smack said:

What you describe sounds like a Throttle Position Sensor type of problem. Does that bike have one?

I think it does have one, haven't found too much on this as a possible cause though. Will keep it in the back of my mind.

boyse7en said:

I've not bothered to run through a list of possible solutions, as I guessed it could be an expensive method of trying to chase an intermittant problem.

I know it only happens after a high speed stint followed by a throttle-off stop (eg, motorway, followed by exit to a roundabout requiring a stop) so i just keep the revs up with the throttle when I pull the clutch in and use the back brake on the last bit of stopping so it doesn't stall. I don't even think about it now.

You have a point, and I could ride around it like you do, but it kills my confidence in the bike, which makes it zero fun to take it out.

Furthermore, I, and you for that matter, should not have to ride around such an obvious design flaw.

Guess I'll have to heckle BMW on Facebook if nothing is forthcoming from the dealers

[catso]

boyse7en said:

Exactly the same as my F800S. I think it's to do with the engine leaning out the mixture for high-speed running, then a sudden closure of the throttle cuts the fuelling and the engine dies.

I've had my bike 6 years now and haven't found a cure... If you find one, I'd love to know!

Sounds like a fuel mapping problem, trying to meet some tree-hugging, save the world standard.

A good ECU mapper could probably sort it and likely find a few hidden ponies too...

[Gunk]

This is a common fault with the S and ST, it's usually either a faulty idle control valve (about £120 to replace) or the fuel tank breather pipes which get hot and then kink. The replacements are reinforced to stop this happening.

[boyse7en]

Gunk said:

This is a common fault with the S and ST, it's usually either a faulty idle control valve (about £120 to replace) or the fuel tank breather pipes which get hot and then kink. The replacements are reinforced to stop this happening.

Would there be any other symptoms of a faulty idle control valve? My bike runs faultlessly other than the issue described by the OP

[Gunk]

boyse7en said:

Gunk said:

This is a common fault with the S and ST, it's usually either a faulty idle control valve (about £120 to replace) or the fuel tank breather pipes which get hot and then kink. The replacements are reinforced to stop this happening.

Would there be any other symptoms of a faulty idle control valve? My bike runs faultlessly other than the issue described by the OP

The symptoms seem to be cutting out when the engine is running hot, so especially in traffic after a long fast run

[cebica]

My dad's f800s had this problem.

We tried to fault find but gave up and px'ed it

It cut out dropping down a gear into bends, and also at motorway speeds. Not exactly confidence inspiring.

Good luck with yours