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Stalling and cut outs !

3K views 20 replies 10 participants last post by  Nakes 
#1 ·
Starting to get on my nerves now.....anyone want to watch a video of me loosing it and killing my f800st. If not I hope for some technical advice.
Bike is an 08 model runs like a dream untill she's been hot for a while: used to take a really hot day and at least 5hrs riding last year, now any warm day I get about 2 hrs riding then she starts.
Symptoms are stalling randomly at first , as she gets warmer engine can die at 3-4 k revs (has happened at 7 k on the odd occasion) a tell tale sign is a feeling of loss of power before she cuts out.And once warm tick over is well rough, great when cold
So far have replaced in order fuel pump, fuel filter, fuel pump controller, TPS and idle actuator pipes (have tested idle actuator)
whats next ?
 
#2 ·
Your symptoms point to fuel more so than idle actuator. One easy thing to try is to remove and clean your roll over valve (tank vent). If it's clogged it can cause a vacuum in the tank. The next time it stalls, open the fuel tank and see if there is negative pressure.

Also wouldn't hurt to check/clean your charcoal filter. You don't have a location in your profile, but if you have a North American bike, they have charcoal filters to catch fuel fumes.

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#3 ·
Thanks for the reply ccramerusc UK based so no canister. Have done as sugested ref: tank vent,next I was going to try the oxygen sensor on the exhaust ?
Or do the fuel filter again as when I replaced the fuel filter 12 months ago now, I really thought I had an improvement, but she soon went back to her old ways. I don't know the history of the bike I'm wondering if the fuel filter could have got cruded up again in less than a year if the bike has sat for a long while with fuel in ?
 
#6 ·
I doubt it's the fuel filter simply because it only happens when it's hot. It's easy enough to clean though, you just pull it out with the pump, let it dry, then vacuum it.

I would also be surprised if the O2 sensor is the issue for the same reason, but I could certainly be wrong. I don't remember anyone in this forum having O2 sensor issues.

To DJ123's point, it could be a spark issue related to the heat. Either plugs or coils, but you can't really test them and coils are expensive to replace (not knowing if they are the issue).

I just really sounds like a fuel starvation issue (losing power and stalling whole at freeway speed). Does it start right back up after it stalls? How about idle when it's hot, especially after it has stalled?

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#7 · (Edited)
Tick over is very good normally but once it has started playing up tick over then becomes poor (hunting) with cutouts. if you try to restart straight away it can be tricky..but will always restart after a 30 secs.
to be clear on my fuel filter theory (and it is just an idea I am throwing out there). I have on occasion needed to fill up with fuel when bike is playing up this seems to give a temporary fix, I think this is probably due to the bike getting a few minutes to cool off, but what If the fuel filter is partially blocked could it be causing the fuel pump to over heat and temporarily fail and fresh fuel acting as a coolant ?? I know this is a bit random now but i am getting a bit insane with it all.
 
#10 ·
Not old then at least. I mean you could try looking at the HT leads/coils but they are expensive - but probably due a change on a 12 year old bike.

Quick way to check for a vacuum is to open the fuel filler cap (after you get a stalling issue) and see if you can feel resistance/hear a hiss when it opens. That would signify a vacuum is being created on the tank and causing fuel starvation.
 
#11 ·
STloon - where do you live? Is it an area with high humidity that might get water in the fuel? It almost sounds like my lawn mower in the spring if I don't put a fuel stabilizer in the gas. Really really hard to keep running.

Chris
 
#12 ·
In the OP you mentioned replacing the TPS. I assume that was the throttle position sensor and not the tire pressure sensor. Because there could be an electrical short somewhere that is triggered when things get hot maybe influencing the TPS which could cause the symptoms you mention (stalling, hard starting, misfire/power loss, etc.). This could be intermittent, so sometimes it runs normal.

The point is that something is limiting the fuel or spark and it is worse when the bike is hot. But there are no symptoms when the bike is cold. I don't know what to tell you.

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#13 ·
There comes a time when it is worth it to take the bike to the dealer and have them fix it.

I did a valve adjustment on my Suzuki Burgman 400 once. Everything went together just fine and I was feeling pretty good...till I tried to start it. Oh my gosh...it barely ran. What did I do???!!! I took everything apart about 4 or 5 times. No change. I asked my friend at work, and he thought I had adjusted them 180 degrees out, or something...and bent a valve. My heart is sinking through all this and it lasted for days.

Finally, I took it to an independent dealer. They checked it out for about six hours. No one could figure it out. At least, they didn't charge for their time. I gave up and dropped it off at the dealershp. About an hour later, I got a call saying I could come pick it up. It was fixed.

The cause? There were about six sensor plugs to take off in order to get to things. All of them were pretty obvious for where they should go. Like one would have 3 wires going to it, and the plug would fit nowhere else. And the wires were exactly the right length to only fit one place. Well, except for two of the plugs. They were identical and the wire length was the same. The Suzuki mechanic noticed that there was a gray male plug connected to a black female plug, and the opposite on another sensor. He plugged them in gray to gray and black to black...and it ran perfectly.

They charged me an hour for labor, and I didn't mind at all.


When I did IT support at one point in my career, the people I helped thought I was a magician. I was able to solve their problem in no time at all. What they didn't realize was that I had been through the same thing ten times already that day. Sometimes, the dealer's technician has seen your problem ten times before and knows exactly where to look.

Chris
 
#14 ·
Bike is booked in with the BMW dealership at the end of the month. I have a good relationship with the main tech guy there as i also have a 2yr old R1200 GS I bought from them and regularly get serviced there, and he has been trying to give me a few ideas.
I have also ordered a new fuel filter and pump 2nd set, as i said in an earlier post I have replaced these before and I seemed to get a temporary fix. I don't know the full history of the bike and I am thinking that It may have had a large amount of crud in tank at some point, enough to block a second filter? and cause fuel pump to over heat and become erratic.
 
#15 ·
Please let us know how it goes. Good luck!

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#16 ·
Hi STloon

Not sure if this is relevant to you, but, I've seen 2/3 YouTube videos where owners have replaced the OEM fuel pump with a Quantum fuel pump , https://www.highflowfuel.com/i-3546...mw-f800st-2005-2013-replaces-16148556074.html

They seem to think the OEM unit (>500 bucks for whole unit from BMW) is weak when hot and can be easily replaced with the Quantum (about 70 bucks).

I've no personal experience of this, living in Ireland it rarely gets hot!
 
#17 ·
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#18 ·
I would be looking at the fuel pump or fuel pump controller.
Failing when hot but ok after filling with (cold) petrol would suggest to me that the fuel pump is intermittent when hot.
Google and search on here good quality replacements are available with out paying BAST (BMW Added Sales Tax) :)
 
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#20 ·
Thanks for all the input, it's been a while and i have tried a few things. The fuel pump controller was replaced by previous owner with newer spec black unit.
So since last post I have replaced fuel pump and filter, still no joy. I have tried riding with the fuel tank open, no joy. I have gone out with a 1 gallon fuel container and added fuel when bike starts stalling instant cure ! Still makes me think fuel pump over heating and being cooled by fresh fuel ??
Bike definitely plays up more when I enter town after riding hard, once it starts to play up the only thing that fixes it is a fresh tank of fuel but if I can get back out on the open road it improves, so I am thinking heat soak in engine area, then I thought about fuel vaporisation in petrol pipe and creating vacuum lock? To this end I have rerouted and insulated the petrol pipe. At the moment the weather is not that warm so bike seems ok. Next time it gets hot I will go for a good run see if anything has changed.
 
#21 ·
Hi STloon, I have a F800ST from 2006 with 50K kilometers and I am experiencing exactly the same problem that you describe. I have read that it could be due to a sensor. There is lots of results on the net about this problem affecting F800 engines, but I haven't found any good solution so far. Please keep us informed regarding the outcome of your interventions.
I have found this and makes sense to me https: //forums.bmwmoa.org/showthread.php?68499-Devilish-stalling-problem-2007-F800ST
 
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