Interesting but my bike is a 2018 1200 Rallye TE.
Exhaust valve, poor cold starting 1200
- Thread starter Engineer
- Start date
Interesting but my bike is a 2018 1200 Rallye TE.
Same behaviour on our 2015 RT, although it is sticking a little, so had to give it a helping hand
Ask yourself how the cat generates its temperature when it’s material doesn’t burn and there isn’t burning fuel running down the pipe, as to the flap bouncing pulses back through the cat that is just ridiculous, its akin to swimming upstream, a very fast running stream.
I am fully aware what valve overlap is and that most if not all performance 4 stroke engines have it to some extent, remember valve overlap only occurs as the exhaust is closing and the inlet is opening and neither is wide open, in fact the piston is at the top of its stroke so there is very little push/draw from the piston. I don't know what the figures are for the BMW but I am aware of 1 engine where the exhaust closes 25’ after TDC, this is considered extreme but in reality it’s about having some useful degree of open right up to TDC.
i dont know what you think you know but on a naturally aspiriated engine (such as a GS) the inlet pressure is only ever going to be close to ambient air pressure (1 bar) the fact that we have compressed this air by a factor of 10 (ish), introduced fuel and significantly heated it means that the volume has increased and this leaves by the exhaust which is a restriction, hence a pressure increase. Anyhow, nothing is going to be drawn back into the cylinder as it is a reducing space as the purpose of the exhaust stroke is to remove the spent combustion charge.
People just don't realise what is going on in their engines, think about what the 1,250cc engine actually means, 1,250cc of air being pumped through the engine every 2 revolutions, so 5,000rpm is over 3,000ltr of air per minute going through the air filter.
You will be hard pushed to find anything really technical on the internet that hasn’t been published by the marketing dept so don't take everything you read as fact, especially when it applies to a sales driven company.
Crikey, but of a mix in there. I didn’t get where you were going re the cat at all, sorry. Cat material burning itself and fuel running down the pipe ? that sounds like a seriously messed up motor.
I’ll respond to a few of the points, then we will just have to agree to disagree before we bore everyone.
I have not claimed the GS exhaust flap is bouncing back exhaust pressure waves. I disagreed with the cat as a block to them as you suggested. It was knut that raised the possibility on the GS in reply to Engineer and I commented that other marques are using servo valves for emission control. Maybe go back and have a read.
I know the Gs uses overlap. It’s probably in line with the norm of starting and finishing either side of tdc. I agree with your comment that it’s really not pulling or pushing at that point and is a more or less a static space . But at the end of the same paragraph you contradict yourself and say it’s happening during the ex stroke and it’s a diminishing space ?
I’m sure you will agree that overlap is generally used to assist evacuation of the cylinder and act as a draw on the inlet charge. Gas always flows from high pressure to low, so in order for overlap to have a positive effect the pressure has to be lower where it’s going to compared to where it’s coming from.
The exhaust gasses leave the cylinder in a hot pressure wave which you can feel if you put you hand over the exhaust, we’ve all done it. A wave by definition is a rising and falling value. You were right that the exhaust is a restriction and along with a piston pushing out the gas you will have a rising exhaust pressure. But overlap doesn’t occur at that point, it’s timed to be on the falling side of the pressure wave towards its lower value ( exhaust valve is almost closed ) where tdc occurs.
So you have an exhaust that is falling in pressure and heat coinciding with overlap. That acts as a draw via the semi open ex valve. It’s basically the same principle as wind ( the weather kind). Cool air ( intake) is drawn towards the lower pressure area caused by the hot air moving away (exhaust).
I didn’t say the cat burned or there was fuel running down the pipe, I asked how you think the cat reaches its temperature when it doesn’t burn or have burning fuel delivered to it (or at least that’s what I meant).
Re the exhaust overlap situation, we will just agree to disagree on the pressure thing as you are convinced and I guess I won’t change that but you might want to consider a cylinder with an open entrance and restricted exit pipe where the ends of both pipes sit at atmospheric pressure and then you detonate a small explosion in the cylinder.
You are right about the pressure wave but that’s done by the time the piston gets to the top of its stroke.
Probably best to leave it there
Well all I can say is my cold starting problem went away - I can think of nothing that changed other than me freeing up the exhaust flap/valve thing - maybe there is an intermittent electrical connection somewhere? temperature sensor? lambda sensor connector? giving the ECU wrong data? We shall see if the problem returns.
Yes very good sticky flap and hot cat, before play with stupid mapping, must check flap first, fuel strving is big problem on leen BMW engines.
When I wrote my first reply, I based my answer understanding that the OP experienced an exhaust flap stuck in open position, and this made an impact on the startup of a cold engine. Then, after a few seconds, the engine reverted to act more like 'normal'.
And after fixing the the flap, stuck in open position, the problem disappeared. I also interpreted this as the flap, when being fixed, reverted to remain closed when engine was started.
My information about the 'ways' of the newest Bosch ECU's was something I stumbled across as I searched for information about how Bosch handled the WB O2 sensors (New in our bikes, but it has been around for a few years in the car world.)
There was a chapter debating the effect of restricting evacuation of the exhaust, containing unburned fuel, especially before the engine warmed up. The EGR valve is the main tool for this in cars, but they also where working on expanding the use of the exhaust flap from being merely a noise restricting tool to a means of restricting the exhaust from all of the exhaust to escape the cylinder, as well as a potential blow back. The blow back may be looked upon a bit of the same effect you get if you try to fill an empty bottle of water and then open up the tap to a full blow.
Anyway, whatever the flap does to the newer engines, keep in mind that for the first few seconds, the fueling is 100% relying on the preprogrammed mapping. The heating of the O2 sensor starts when the engine has started, not sooner, and the warm-up time is typically 10 - 15 seconds.
Now... If the engine is set up for a more than average exhaust remaining in the cylinder, motivated by less pollution and less filling up the cat by unburned gases (which is very damaging for the cat), the only means of doing this for a short periode of time is by using the flap, as, even if the flap allows some exhaust to by pass, the pipes will still be flooded by exhaust above average, a bit like trying to get off a train when the apron is congested by people blocking the exit. In this scenario, an open flap would allow for less remaining exhaust in the cylinder, thus allowing for more oxygen entering the cylinder.
If this theory is real (and also, keep in mind that Bosch has claimed to be working on this,) the fueling at this stage is preprogrammed for less oxygen entering the cylinder, hence adding less fuel, and no feedback from the O2 sensor, as it's still warming up. The engine would be running rough and would be needing more fuel, hence opening up the throttle. Opening the throttle means opening of the flap, allowing for a preprogrammed sceniario where the flap would open anyway, which means a pre-program to add fuel based on a higher percentage of oxygen entering the cylinder.
And then, after the O2 sensor is warmed up, the fueling would be adjusted based on feedback from the exhaust, and the throttle may be released, allowing for a smooth running engine at idle even with the flap stuck in open position as the feedback from O2 sensor now would compensate the fueling.
If after testing, hopefully sometimes this weekend, shows that the flap is open also when starting and running a cold engine, this theory will be shot, and we may conclude that the whole experience by the OP was merely a coincident.
Time will show...
PS.
I would also like to add that I do appreciate this debate, where everyone is debating and challenging the technical part of what's happening rather than clogging the debate with nonsense
And after fixing the the flap, stuck in open position, the problem disappeared. I also interpreted this as the flap, when being fixed, reverted to remain closed when engine was started.
My information about the 'ways' of the newest Bosch ECU's was something I stumbled across as I searched for information about how Bosch handled the WB O2 sensors (New in our bikes, but it has been around for a few years in the car world.)
There was a chapter debating the effect of restricting evacuation of the exhaust, containing unburned fuel, especially before the engine warmed up. The EGR valve is the main tool for this in cars, but they also where working on expanding the use of the exhaust flap from being merely a noise restricting tool to a means of restricting the exhaust from all of the exhaust to escape the cylinder, as well as a potential blow back. The blow back may be looked upon a bit of the same effect you get if you try to fill an empty bottle of water and then open up the tap to a full blow.
Anyway, whatever the flap does to the newer engines, keep in mind that for the first few seconds, the fueling is 100% relying on the preprogrammed mapping. The heating of the O2 sensor starts when the engine has started, not sooner, and the warm-up time is typically 10 - 15 seconds.
Now... If the engine is set up for a more than average exhaust remaining in the cylinder, motivated by less pollution and less filling up the cat by unburned gases (which is very damaging for the cat), the only means of doing this for a short periode of time is by using the flap, as, even if the flap allows some exhaust to by pass, the pipes will still be flooded by exhaust above average, a bit like trying to get off a train when the apron is congested by people blocking the exit. In this scenario, an open flap would allow for less remaining exhaust in the cylinder, thus allowing for more oxygen entering the cylinder.
If this theory is real (and also, keep in mind that Bosch has claimed to be working on this,) the fueling at this stage is preprogrammed for less oxygen entering the cylinder, hence adding less fuel, and no feedback from the O2 sensor, as it's still warming up. The engine would be running rough and would be needing more fuel, hence opening up the throttle. Opening the throttle means opening of the flap, allowing for a preprogrammed sceniario where the flap would open anyway, which means a pre-program to add fuel based on a higher percentage of oxygen entering the cylinder.
And then, after the O2 sensor is warmed up, the fueling would be adjusted based on feedback from the exhaust, and the throttle may be released, allowing for a smooth running engine at idle even with the flap stuck in open position as the feedback from O2 sensor now would compensate the fueling.
If after testing, hopefully sometimes this weekend, shows that the flap is open also when starting and running a cold engine, this theory will be shot, and we may conclude that the whole experience by the OP was merely a coincident.
Time will show...
PS.
I would also like to add that I do appreciate this debate, where everyone is debating and challenging the technical part of what's happening rather than clogging the debate with nonsense
When I wrote my first reply, I based my answer understanding that the OP experienced an exhaust flap stuck in open position, and this made an impact on the startup of a cold engine. Then, after a few seconds, the engine reverted to act more like 'normal'.
And after fixing the the flap, stuck in open position, the problem disappeared. I also interpreted this as the flap, when being fixed, reverted to remain closed when engine was started.
My information about the 'ways' of the newest Bosch ECU's was something I stumbled across as I searched for information about how Bosch handled the WB O2 sensors (New in our bikes, but it has been around for a few years in the car world.)
There was a chapter debating the effect of restricting evacuation of the exhaust, containing unburned fuel, especially before the engine warmed up. The EGR valve is the main tool for this in cars, but they also where working on expanding the use of the exhaust flap from being merely a noise restricting tool to a means of restricting the exhaust from all of the exhaust to escape the cylinder, as well as a potential blow back. The blow back may be looked upon a bit of the same effect you get if you try to fill an empty bottle of water and then open up the tap to a full blow.
Anyway, whatever the flap does to the newer engines, keep in mind that for the first few seconds, the fueling is 100% relying on the preprogrammed mapping. The heating of the O2 sensor starts when the engine has started, not sooner, and the warm-up time is typically 10 - 15 seconds.
Now... If the engine is set up for a more than average exhaust remaining in the cylinder, motivated by less pollution and less filling up the cat by unburned gases (which is very damaging for the cat), the only means of doing this for a short periode of time is by using the flap, as, even if the flap allows some exhaust to by pass, the pipes will still be flooded by exhaust above average, a bit like trying to get off a train when the apron is congested by people blocking the exit. In this scenario, an open flap would allow for less remaining exhaust in the cylinder, thus allowing for more oxygen entering the cylinder.
If this theory is real (and also, keep in mind that Bosch has claimed to be working on this,) the fueling at this stage is preprogrammed for less oxygen entering the cylinder, hence adding less fuel, and no feedback from the O2 sensor, as it's still warming up. The engine would be running rough and would be needing more fuel, hence opening up the throttle. Opening the throttle means opening of the flap, allowing for a preprogrammed sceniario where the flap would open anyway, which means a pre-program to add fuel based on a higher percentage of oxygen entering the cylinder.
And then, after the O2 sensor is warmed up, the fueling would be adjusted based on feedback from the exhaust, and the throttle may be released, allowing for a smooth running engine at idle even with the flap stuck in open position as the feedback from O2 sensor now would compensate the fueling.
If after testing, hopefully sometimes this weekend, shows that the flap is open also when starting and running a cold engine, this theory will be shot, and we may conclude that the whole experience by the OP was merely a coincident.
Time will show...
PS.
I would also like to add that I do appreciate this debate, where everyone is debating and challenging the technical part of what's happening rather than clogging the debate with nonsense
Earlier in the thread I posted that I have already looked at a 2015 and my 1250 to see what the flap is doing. On the 1200 the flap is actually just about stuck open and it has been this way for 1000s of miles and many cold starts with no impacts (its a blood bike). Onto my own 1250 EU4. The flay cycles on ignition on, from open to closed then open. On starting, (after the engine is running) it moves to 3/4 closed. On switch off it moves slightly towards open, but not fully open, so not sure if this is being to stick. But as soon as ignition is back on, it cycles as before. So this still could be for noise, rather than anything else. Will be good to get your views. Interesting thing is a friend told me that a BMW tech had told him that on the 21 1250s, there is no longer an engine warning light for a stuck flap. He is taking his RT in for a new flap on his 2020 bike in a few days, bike has only done around 1.5k miles I believe
Earlier in the thread I posted that I have already looked at a 2015 and my 1250 to see what the flap is doing. On the 1200 the flap is actually just about stuck open and it has been this way for 1000s of miles and many cold starts with no impacts (its a blood bike). Onto my own 1250 EU4. The flay cycles on ignition on, from open to closed then open. On starting, (after the engine is running) it moves to 3/4 closed. On switch off it moves slightly towards open, but not fully open, so not sure if this is being to stick. But as soon as ignition is back on, it cycles as before. So this still could be for noise, rather than anything else. Will be good to get your views. Interesting thing is a friend told me that a BMW tech had told him that on the 21 1250s, there is no longer an engine warning light for a stuck flap. He is taking his RT in for a new flap on his 2020 bike in a few days, bike has only done around 1.5k miles I believe
Interesting. And thank you for your input
When it boils down to it, there will always be a bit of guess work and a bit of assumption on all of us, as BMW doesn't really advertise in details how the ECU works, so it is down to picking pieces of information from here and there and adding it all up and then see if it makes sense in real life.
As for the flap still being for noise only, I will not insist on anything. However, ask your self a couple of questions:
If the flap is fully or even partly closed, this will surely restrict the flow of exhaust, as compared to a fully open flap? Then, this will also affect the exhaust escaping the cylinder.? And if so, this will affect the amount fresh air (and oxygen) entering the cylinder?
If the flap serves as a noise killer only, then why does it close only at idle, only to open up once the throttle is opened and the engine really starts to make noise?
As for engine warning light for the flap:
My -15 had a stuck flap. But the only warning that came out of it was only the fault-code that could be read out by diagnostics. Nothing visible to the rider from the instrument panel. For the 1250 I can not say, as there has never been a problem with the flap on my bike.
Interesting. And thank you for your input
When it boils down to it, there will always be a bit of guess work and a bit of assumption on all of us, as BMW doesn't really advertise in details how the ECU works, so it is down to picking pieces of information from here and there and adding it all up and then see if it makes sense in real life.
As for the flap still being for noise only, I will not insist on anything. However, ask your self a couple of questions:
If the flap is fully or even partly closed, this will surely restrict the flow of exhaust, as compared to a fully open flap? Then, this will also affect the exhaust escaping the cylinder.? And if so, this will affect the amount fresh air (and oxygen) entering the cylinder?
If the flap serves as a noise killer only, then why does it close only at idle, only to open up once the throttle is opened and the engine really starts to make noise?
As for engine warning light for the flap:
My -15 had a stuck flap. But the only warning that came out of it was only the fault-code that could be read out by diagnostics. Nothing visible to the rider from the instrument panel. For the 1250 I can not say, as there has never been a problem with the flap on my bike.
I can confirm that the EU4 1250s have an engine warning light now if the flap is stuck, which surprised me as it looks like they have binned that idea for the 21 year 1250 and just gone back to a fault code like my 2014 did. The flap testing I did showed the flap to open slightly at idle and above and open fully when the revs rise. Thus on the noise front, when on low throttle, probably riding through built up areas, less noise, but out in the open more noise, which kind of works in my head for noise pollution. Hence the view that a stuck flay doesn't matter at all to the engine performance and that view was also passed onto my friend last week, when he asked if could use his 1250 with the engine light on and flap stuck open, they said it wouldn't impact performance and was fine to ride until they could get the replacement headers in.
The service manager at my BMW dealer said that my cold starting issue was almost certainly caused by the flappy exhaust valve being stuck open - so knutk your hypothesis is probably correct
My cold starting issues were at morning temperatures of below about 5C - at higher ambient temperatures then maybe the flap being open is not so important?
My cold starting issues were at morning temperatures of below about 5C - at higher ambient temperatures then maybe the flap being open is not so important?
The service manager at my BMW dealer said that my cold starting issue was almost certainly caused by the flappy exhaust valve being stuck open - so knutk your hypothesis is probably correct
My cold starting issues were at morning temperatures of below about 5C - at higher ambient temperatures then maybe the flap being open is not so important?
Ok whatever. Our blood bikes work all year around at winter temperatures. Never had any starting issues with the valve stuck open. Your BMW tech has a different view to the ones I have spoken too at two different dealers. But to be honest, this has run its course now. Believe what you want.
Not really sure the dealer techs would be any the wiser to be honest. It’s a detail they probably don’t really need to know.. I suspect you might get a different answer from a different tech at the same dealer on any given day.
I'd like to see some definitive information from BMW or Bosch, until then we'll have to try to reason it out ourselves.
you have already, it was fuel starving.
and it went away once I unstuck the exhaust flap and let it close?
Yes O2 sensors ecu and flap and catalictic all doing job as design now, open is ok, but totally closed not so good.
Because the flap was stuck open the mixture was too lean for a cold start?
Not sure what kind of an Engineer you are or if you are, but why is your bike special and all the evidence already given shows that the flap stuck open has little or no impact on cold starting. I'll tell you once more, the flap has been stuck open on one of our blood bikes for a couple of years, it has never had any cold start issues and gets used all through the winter. My first 2014 bike had a stuck flap that was open for over a year until I got it changed, again I didn't even know it was open, no starting issues.
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