What exactly is Surging?

[malcolm]

I've heard and read alot about this surging phenomina.

 

As far as I'm aware, neither my R or RT do this.

 

Can some kind sole tell me just what surging is. Maybe mine does but I've not noticed it and I thrash mine.

[Boffin]

Can some kind sole tell me just what surging is. Maybe mine does but I've not noticed it and I thrash mine.

That is why you don't notice surging, if your bikes do it. Some do, some don't.

 

Surging is a feeling like the bike is constantly speeding up and slowing down. It is felt when the bike is on constant mid-throttle, ususally between 3000-4000 rpm. If you ride the bike outside these limits you do not feel any issue.

 

Andy

[George]

It was at it's worst on the early R1150RT's, I know as I owned one, a Techlusion unit soon sorted it.

Here is the problem:

The fundamental problem is the Motronik 2.4 engine management system (EMS) for the BMW R1150RT is optimised to provide the lowest possible emissions and noise in the 3,000rpm to 4,000rpm range. This is accomplished by both retarding the ignition and running the engine in the leanest possible state. Not all bikes surge. Not all riders notice the surging. More than one factor can contribute to surging. Even a good running bike will exhibit some surging. In the cruise zone (3,000rpm to 4,000rpm) the EMS will every several seconds make a change in the parameters trying to obtain optimal emissions. This will cause the engine speed to vary by 50 to 100rpm

Tom Hankinson

[DEF]

It was at it's worst on the early R1150RT's, I know as I owned one, a Techlusion unit soon sorted it.

Here is the problem:

The fundamental problem is the Motronik 2.4 engine management system (EMS) for the BMW R1150RT is optimised to provide the lowest possible emissions and noise in the 3,000rpm to 4,000rpm range. This is accomplished by both retarding the ignition and running the engine in the leanest possible state. Not all bikes surge. Not all riders notice the surging. More than one factor can contribute to surging. Even a good running bike will exhibit some surging. In the cruise zone (3,000rpm to 4,000rpm) the EMS will every several seconds make a change in the parameters trying to obtain optimal emissions. This will cause the engine speed to vary by 50 to 100rpm

Tom Hankinson

 

Surging might be better called RPM hunting or poor drivability.

 

As stated by Tom, BMW boxers (and most bikes for that matter) have very sensitive response to inputs from the throttle (your right hand). When you change the throttle setting, the new throttle position is detected by the TPS, the little black box on the left throttle body, and sent to the Motronic. Then, the engine management computer changes injection pulse duration (adjusts fuel delivery). Then, the Lambda sensor (if so equipped…BMWs are so equipped) provides new exhaust gas information (oxygen content) to the Motronic engine management computer to help further control fuel delivery to the injectors. Also, as the engine warms and the oil temperature and air temperature change, this information is also fed to the Motronic for further fuel delivery changes. So, you see there is a lot going on in the engine management computer (Motronic).

 

When your engine is warm, in a lower gear and at low to mid RPM steady throttle, the Motronic is on the verge of going from open loop to closed loop engine management. The Motronic’s job is to maintain correct stoichiometry (fuel/air ratio) at any RPM and engine load…and, it is a tough job and it must be done so that the engine meets current EPA, CARB or other emission requirements.

 

In SOME boxers, (not all….it depends on how well the bike is tuned) the conditions are such that a RPM variation occurs even though you are not changing the throttle input. The engine hunts back and forth sort of chasing the correct fuel delivery and the result is what we boxer fans call surging.

 

There is a way to cure it and it is dead simple. It involves no more than some minor factor specification adjustments and using a different brand of sparkplug.

 

Later boxers (the dual spark versions) cure this surging condition by providing better ignition of the fuel/air mix at combustion. Also, Motronic mapping is improved in boxers as the engine has evolved over the past few years (I do not know the specifics of each Motronic version and to what extent it changes engine drivability) but, BMW has been chasing this difficulty for as long as owners have complained about it.

 

Some owners cure this malady with a new ECM (a chip)…in other words, they throw away the Motronic that BMW provided and substitute a new EPROM (an addressable device…your OE Motronic is NOT addressable) with different fuel delivery maps but, what typically happens is that the new chip (programmable with a cable between the chip and a laptop computer) allows remapping or reprogramming with new fuel delivery and ignition timing information…in other words, a brain transplant that allows the tuner to control the fuel delivery and ignition timing settings. The success of this procedure is to a large part, dependant on the skill of the tuner who is tweaking the maps for better performance, better engine drivability and more power. Therefore, your boxer may be at the mercy of a wrench head who knows little about boxer thermodynamics, engine reliability, BMEP curves for the boxer and other engine variables. There are some tuners out there who are skilled and use care and discretion when remapping.

 

In my opinion, and this is MY opinion only, this is NOT the way to maximize engine drivability. Also “chipping” your boxer is not cheap. Some boxer owners claim the new chip provides increased power…could be, but it comes at the expense of more fuel, increased engine emissions and potentially reduced engine life. Oh, and BMW doesn’t like it either. It voids your factory warranty.

 

If you object to the drivability of your boxer, the cure is simple.

 

Oh, and you can merely change the CAT plug to access different fuel maps in your existing Motronic…the cost is only a few bucks.

 

In closing, you may be able to eliminate surging by changing brands of fuel, installing different spark plugs and performing some careful adjustments on your boxer.

[malcolm]

Thanks to everyone for their input on this surging issue.

 

I noticed a thread mentioning the subject last week and decided to ask you guys just what it is exactly.

 

You see I'd been away with a few blokes the week before and I described to him a riding problem. He said he had just put this addressable eprom under his seat (like what one of you were talking about higher up in this thread); said he'd paid AU500$ for the device and said it would solve my problem... he called it "surging".

 

After reading your responses it would appear my friend doesn't actually have a surging problem. He has a new R1200RT.

 

I certaily don't have a problem between 3 & 4000 revs. No complaints at all in this rev range (cept she likes to hang around the 5 to 6000 rev range. I call it "Party Zone")

 

I described my problem to him like this...

 

when trying to go real slow... like in a procession or in very slow moving traffic the throttle response is so sensitive I tend to move forward in jerks.

 

I try real hard to twist the damn thing very slowly so I slightly increase my speed, or visa versa, back off very slightly to decrease my speed, but my 05 R1150RT lunges forward or back creating an unpleasant JERK.

 

Do any of you know what I'm talking about and have any suggestions?

[Boffin]

The (necessary) slack in the drive train, coupled with a light flywheel is the culprit here. The engine has masses of torque, even down to low RPM and so accelerates quickly, leading to that jerk. The best bet when moving, is to get into second gear early - it is amazing how slow you can go in second. The higher gearing damps out the jerkiness.

 

Andy

[DEF]

The (necessary) slack in the drive train, coupled with a light flywheel is the culprit here. The engine has masses of torque, even down to low RPM and so accelerates quickly, leading to that jerk. The best bet when moving, is to get into second gear early - it is amazing how slow you can go in second. The higher gearing damps out the jerkiness.

 

Andy

 

Excellent advice, also, a very careful valve lash adjustment can help. Also, I run Autolite plugs (3923s...yours may be different). My boxer (A single spark model) is dead smooth and the single plug models were (are) the worst surge culprits in the recent boxer series.

 

Oh wait....you chaps are from GB....and here, I am from the colonies........more advice....change your CAT plug to provide a slightly richer Motronic fuel map selection.

 

Don't spend money for an addressable chip when your Motronic already has additional maps you can access....save your money and buy your wife some flowers...the flowers will help your riding considerably (Heh-heh).

[Ken H.]

The best bet when moving, is to get into second gear early - it is amazing how slow you can go in second. The higher gearing damps out the jerkiness.

Exactly. The boxer is very torquey, and short shifting it in stop-and-go stuff can be a tremendous help.

[malcolm]

Thanks Andy. I'm going out today to see just how slow I can go in 2nd.

 

Sounds like you have the right idea. TA

[malcolm]

Ken, "short shifting" ?

 

what do you mean?

 

changing quickly into second after take-off ? When you'd be thinking you could do well to stay in first?

 

Let me know pls

[ShovelStrokeEd]

Malcom,

That is exactly what Ken means, in addition, not downshifting into first when moving in slower traffic. You can go right down to idle RPM in second and only be moving at less than 5 mph. Of course, you can't whack the throttle open from there but who, if they have any feel for machinery, would?

 

The main advantage to using second instead of first is that it remove, as Boffin pointed out, a lot of the herky-jerky movement. First requires very fine and precise throttle control to maintain steady progress at a walking pace, second, not so much.

 

The same applies to slow speed U-turns. I frequently use second there, even on the Blackbird which will do nearly 100 mph in second gear. Throttle transitions are just that much smoother.

 

Back on topic, surging will often show itself when running right in the 2800-3200 RPM rev range. In particular in third gear. The simple solution is to downshift and, as others have stated, ride around it. The primary cause is related to the bike, and the Motronic, operating in closed loop mode, defined as about 15% throttle opening. The motor, under feedback from the O2 sensor constantly is switched back and forth from rich to lean. As it turns out, the feedback loop gets out of synch with the engine demands at those speeds and the swings from rich to lean get to large, thus the bike hunts for a steady RPM, accelerating as the motor goes rich and then bogging as the motor goes lean. This is not as evident on multicylinder bikes as the power pulses are smaller and more frequent. Same goes for cars which have the additional advantage of much more mass to damp the power transitions.

 

I'll betcha a nickel I can cure ANY surging BMW motorcycle just by the simple solution of making a new flywheel that weighs about 4 lbs more. Of course then I'd have to listen to complaints of no throttle response and sluggish acceleration. You pays your money and takes your choice.

[Boffin]

Ken, "short shifting" ?

 

what do you mean?

 

changing quickly into second after take-off ? When you'd be thinking you could do well to stay in first?

 

Let me know pls

 

The term 'Short-Shifting' means changing up before the optimal revs. Used a lot by racers to control wheelspin, useful on the road for lazy rides or for instances like this.

 

Andy