Very intermittent lurch around 4500rpm

2010 Hexhead, twin Cam 38 000 miles
As those on the bakermans weekend ride may recall I had a few issues with my bike. Full tank of fuel to start.
I went for an overtake in second and at around 6000rpm I got a sudden deceleration from the bike. Almost like someone had stuck a broom through the rear wheel. Quite a violent lurch from power being cut. Instruments stayed on, bike then continued to ride. I initially thought I had hit the rev limiter but I am pretty sure it was below 7500rpm (I have hit the limiter before so do know what it feels like). It happened again that day at around 4500 revs in third or fourth. At one point I rode to 6500rpm in 2nd and then close to that in third and nothing happened. Later on changing down at around 5000 to 5th gear it stalled and I had to come to a stop and restart it. Rest of the ride was me being very tentative on the power and keeping it below 4500rpm. It seemed ok but was defo not confidence inspiring soon as I went up past those revs. It was a real wallop with bike lurching and head dipping! Anyhow, Saturday I ran it very close to dry (not intentinally, just couldn't find a station!). Re filled with super andhoped for the best.
Sunday's ride home went well, for the most part until bike was warm (again I pushed it to see if the error could be repliucated but as much as I tried, it wasn't having it). Low and behold, cruising up a gentle incline in 5th I rolled on gently and wham! same thing. Gear down, calm head and carry on. Further along, it happened to stall again in third between lights and I had to pull over and re start the bike. Sotook it to Park Lane, explained my predicament and they said they'd test it. Head mechanic said there was nothing showing in the ECU readout. I asked them to keep it and ride it to see if they could find the fault. He had it a week, we had 2 or 3 conversations and he still couldn't get the bike to do it. I collected it a week ago, and after 13 miles I managed to get it to lurch violently after a slow roll on at 4500rpm in 4th, then when I changed down and made a turn, it cut (hiccup like) again in 3rd. Its now back with Tony at P Lane! So irritating. Nothing shows up in logs, clocks stay on but I lurch forward quite badly everytime. Not the best of thoughts as you open up towards the end of a bend. Ideas ?

It's sudden nature sounds something electrical. Check the ECU connections, ignition switch and engine kill switch.

Sounds to me like a TPS fault. Can you swap it out with a known good one?

all good, but these would surely show up in the 911 readout? no faults recorded. . I agree it must be something that says"no more" But it would occur more often as well since it happened at different revs, ie different vibratory frequencies if it was a loose connection?

Not being a GS911 owner I'm not sure how it would look on the real-time graph readout that is on the Hexacode webpage. However, if the wiper arm in the TPS is perhaps 'picking up' something and breaking contact the other part, the ECU may read it as at idle and that is being felt as the engine cutting out and not registering a fault. I know its a lot of Ifs and perhaps but I had a similar event on my Fiat Uno Turbo and they said there was no fault on the ECU. I changed the TPS for one known to work and it cured it. Subsequent examination of the TPS innards revealed bits of insulation floating around inside and the odd bit of scoring on the coil tracks
As for cutting out and having to restart sometimes under certain conditions ie rapid throttle shut off, the engine will die as the idle steppers cannot react quick enough....well it has happened to me a couple of times and as such it is true

If the TPS is worn the fuel injection and ignition map will go to pot. I doubt the ECU will log a fault for the TPS as it's a constantly variable input to the ECU not a given value.

ok, makes sense. I ll now google the throttle potentiometer sensor ? tps?

adventuredon said:

ok, makes sense. I ll now google the throttle potentiometer sensor ? tps?

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adventuredon said:

ok, makes sense. I ll now google the throttle potentiometer sensor ? tps?

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Throttle Position Sensor, to be pedantic (although as mentioned, it is a potentiometer )

Park Lane called me today to say they have not been able to locate or replicate the fault as of yet. They did now say that an error code shows an intermittent fault with the side stand switch. It also has a clip that is missing and it may be damaged. BM won't test it, just replace it...(I know it could well have worked loose as I did take my stand off recently to re spray the side stand ). I know that I checked how far my side stand needed to be pushed down before the engine cut out as this was one of the things I thought it could be, and I had to get the SS about a third of the way down before it cut out. Anyhow, BMW say that it may be the fault but what I am disappointed in is:
- surely the SS kill switch is an on / off switch. If the sensor is faulty, surely it'd just kill the engine, not kill it, then allow it to start again, a la switching an old engine off that slowly dies and at the last minute you give it fuel and it starts again..)?
- I asked BMW to clear the logs and go ride it and see if the switch error showed up again in the logs without a lurch being felt, then I would assume it could not be the fault I reported (so far they can't get a lurch..). BM were not keen to do this for some or other reason
- why is it only now showing up in the logs (assuming this is the problem), or did they not read all logs in the first place
- why didn't the mechanic think of this or look at it with eyes when logs showed nothing last time they had the bike
- So I am having to replace the faulty switch which may or may not even cure the problem that they cannot as yet find!

Yet another example of poor programming in the canbus system. Additional code need not be costly but the designers are still using the same sticks and string they had for the old airheads.

to a certain extent, the problem they have now sort of identified, highlights their reliance on code to diagnose a fault. What happened to a proper look see?

In addition, the SS has not shown them my fault I reported!

adventuredon said:

BM were not keen to do this for some or other reason
- why is it only now showing up in the logs (assuming this is the problem), or did they not read all logs in the first place
- why didn't the mechanic think of this or look at it with eyes when logs showed nothing last time they had the bike
- So I am having to replace the faulty switch which may or may not even cure the problem that they cannot as yet find!

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It's bloody laziness on their part or they don't believe there is a fault reason I do self servicing as much as poss bikes & van lol I hope you get it sorted nothing worse than a intermittent fault.

Can someone please tell me if the ss switch is indeed an on off switch, or can there be middle ground as explained above?

If I understand your question correctly the side stand switch is a exactly that, a switch I.e. On or Off. The ECU reads it as a 0 or 1 value. The GS911 also gives a side stand switch state as 0 or 1.
Regarding the kill the engine and then you have to restart it question, if you are riding along and you push the side stand down about a third the engine will cut out. Return the side stand to the up position it will restart by virtue of the bike being in gear and going forward this turn the engine.

Thanks Rusty, that's what I thought. its pregnant or not, on or off. I dont get the same feeling when the lurch occurs as when I have bump started my bike before. S Maybe the helper who called me didn't really understand what I was trying to ask - in that if the side stand (or loose sensor or whatever was causing the intermittent fault to show on the 911 caused the lurching, when it returned I would feel a very similar feeling to bump starting the bike. It doesn't so I kind of think this is a red herring for the mechanic. BTW, does each fault have a date stamp ? And is each fault overwritten by latest event, or is a running log kept until manually cleared by mechanic?

adventuredon said:

Thanks Rusty, that's what I thought. its pregnant or not, on or off.

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Thats the way its supposed to work but not necessarily what is actually happening. Depends on the detailed design and the nature of the fault but its quite possible to get an internittent short or current leakage via bad contacts and dirt. I dont know whether the circuit functions with the switch open or closed but the best way of finding out if that indeed is the problem is to jury rig it permanently in the run position and see if your problem goes away.

I have sympathy for the grease monkeys trying to find an intermittent problem in a complicated systemn they likely dont understand anyway. You dont get to end up as a mechanic if you are the top of your school class.

FWIW the "lurching" will only feel like bump-starting if you pull the clutch in and allow the engine to stop, then let it out again to start the engine turning.

You can "simulate" a SS switch problem by using the Kill switch to cut the sparks and fuel supply for a few seconds.

Your description of feeling as though someone has stuck a broom in the rear wheel has me thinking the problem may be mechanical, either in the engine or transmission (final drive failure, anyone?) as that is exactly how it felt when a (roller bearing) big end broke up on a Honda 250 I had the misfortune to own in the 70s. It kept running for a couple of weeks, partially locking each time one of the (now not very round) rollers jammed or chewed up a piece of bearing cage...

Roymondo said:

FWIW the "lurching" will only feel like bump-starting if you pull the clutch in and allow the engine to stop, then let it out again to start the engine turning.

You can "simulate" a SS switch problem by using the Kill switch to cut the sparks and fuel supply for a few seconds.

Your description of feeling as though someone has stuck a broom in the rear wheel has me thinking the problem may be mechanical, either in the engine or transmission (final drive failure, anyone?) as that is exactly how it felt when a (roller bearing) big end broke up on a Honda 250 I had the misfortune to own in the 70s. It kept running for a couple of weeks, partially locking each time one of the (now not very round) rollers jammed or chewed up a piece of bearing cage...

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I think the difference between the bump start feeling and your particular cutting out may be a crucial difference. As Raymondo says if it feels a lot more harsh then it would start to indicated something mechanical as that would be the only thing that could produce that amount of deceleration. Although if it was the drive train side, I would have expected the rear wheel to lock and perhaps a skid as well. Also (and bear with me on this) when you open the throttle and expect to excelerate and your bike does exactly the opposite it can feel very much exaggerated. Your body is tensed up ready to absorb a force in one direction but it actually come in the opposite one....type thing!

I hear you, but it generally happens mid roll on, or mid way from the speed I was at and speed I want to be at. Usually when I am gently opening up, especially after it happened the first time I lost the urge to wind it on too quickly! I haven't noticed a skid or stop, go, splutter feeling as you usually get when bumping. Does the gs 911 timestamp errors?