backfiring when engine braking

[m_stock10506]

This is from bmbikes.co.uk web site:

BMW R1100RS
Start of Production: 1992
Ignition System: Electronic ignition, Bosch Motronic MA 2.2

BMW R1100S
Start of Production: 1998
Ignition System: Electronic ignition, Bosch Motronic MA 2.4.

The data on the Motronic is consistant with RealOEM and with BMW Parts Fiche on the MaxBMW web site.

The MA 2.2 doesn't learn or adapt, the MA 2.4 does learn and it does make changes to the fueling data.

 

[happy wanderer]

--"pop" is still there--tomorrow I will start it on the center stand and check all the muffler connections to make sure I assembled it properly--will let everyone know if anything changes

Appreciate all the feedback on this--love this bike

Tony

When you check things out make sure the bolts holding the front header pipes to the heads are secure. I don't think anything else holds up the front headers until they join together and connect to the cat and exhaust with the clamp. Maybe they got loose somehow during replacement of the heavy stuff.

 

[aapasquale]

When you check things out make sure the bolts holding the front header pipes to the heads are secure. I don't think anything else holds up the front headers until they join together and connect to the cat and exhaust with the clamp. Maybe they got loose somehow during replacement of the heavy stuff.

will do this today--didn't loosen headers when muffler was replaced, but will check this closely--thanks

 

[rdhudson]

No Smarter Motronic 2.2

Being new to the R1100R I accept that my bike's 2.2 Motronic can't learn. So many sites make this clear that I accept it. Apparently in contrast to my observation the Earth really does rotate and is also not flat. In my earlier post I did 2 things to get the bike running well. 1. I pulled the #5 fuse, and, 2. I replaced the Bosch plugs with Autolite 3923's. Remember when I restarted the bike it ran much worse than before those two changes. Almost did not run above idle- no acceleration above idle, cut out very badly etc. I then ran it at constant speed through the range. (see my prior post) and the bike dramatically improved.
So oo o. What did happen? Injector cleaner -(techron) finally worked? Cat cleared of carbon? Plugs began sparking after 10 minutes? Cylinders cleared? What should I do if this poor run-ability rears its head again? I'd be tempted to pull the fuse again.... how could I be so ignorant?
HELP
This is from the earlier post "Throttle Response" (I put in two Autolite 3923s, pulled the #5 fuse to reset the Motronic FI and started it up. Nice idle, then I tried to ride. Bucking sputtering, cut out, backfire. I turned back to home hoping to get back a mile when I remembered that pulling the FI fuse requires the Computer to learn a new map for running the bike. Aparently driving for a while at a constant RPM helps it to do that (read above). I tried that and in a couple of miles it ran much better, better than it had for me since I had first left the seller's yard. Within 12 miles I had a wonderful machine, power, smooth acceleration, no skipping or any bad symptoms at all. I couldn't even find that guy you all say often goes along... Surge or what ever your name for him is. THANKS ALL you are the BOMB!
Ralph)

 

[Bmandiego]

I don't believe this has anything to do with fuses, or twisting throttles, or riding for 20 miles.

I agree with Paul.

My own belief is to make a small voodoo doll of the bike, and when a problem presents itself, twist the affected part on the doll and see if it helps. then try the stuff on this post and see if any of this stuff does any better.
Happy Halloween.

 

[aapasquale]

hi all

started bike and checked for any leaks at the heads and the one connection between the headers and muffler--no leaks--am in the process of doing major and minor servicing (36,000 miles)--will do valves and sync later this week--will let you know what's up after that

Tony

 

[ANDYVH]

Good that you found no leaks. But aside from that, unless you change the fuel/air mix, the popping will persist.

Next time you are out riding, test it. Get up to speed and then decel in a manner to cause the popping. Then pull in the clutch, and the popping stops.

Its caused by the bike momentum trying to "push" the engine to breathe harder against the closed throttle/lean condition. As the bike slows in gear, clutch out, the turning rear wheel causes the engine to go to high vacuum state, trying to suck in more fuel/air. But it can't get enough for ignition to take place. Until the engine turns over enough times to build up some fuel/air mix that does ignite. Most often that happens when the exhaust valve is open and the sudden ignition "pops" into the exhaust chamber.

Its also one reason BMW makes exhausts with large oversize canisters, for sound dampening. All the aftermarket exhausts have smaller canisters, but they also make the popping sound more evident because of less sound dampening capability.

 

[jammess]

There is no such thing as a 1994 R1100S. Introduced in 1999 I believe. The R1100RS was introduced in 1993 as a 1994 model. They don't learn in the sense that the later Motronic devices do. I don't believe this has anything to do with fuses, or twisting throttles, or riding for 20 miles.

Morning Paul,
Sorry about referring to an R1100S as a '94 model. I agree that resetting the 2.2 Motronic as if it were a 2.4 version is largely a waste of time. That said, I also stated my belief that a 2.2 Motronic doesn't "learn" and I should say that is just my opinion based on observations of my '94 RSL which was produced in June of '93. Also, I operate my RSL without the O2 sensor connected and CO potentiometer installed so any learning capability is most likely nullified anyway. I wish we had good reliable info from Bosch about these Motronics but that is wishful thinking and probably only useful to an habitual tinkerer which I, no doubt, am one.

Haven't heard from Roger04 lately. Hope he made it through the hurricane OK.

 

[happy wanderer]

Being new to the R1100R I accept that my bike's 2.2 Motronic can't learn. So many sites make this clear that I accept it. Apparently in contrast to my observation the Earth really does rotate and is also not flat. In my earlier post I did 2 things to get the bike running well. 1. I pulled the #5 fuse, and, 2. I replaced the Bosch plugs with Autolite 3923's.
Ralph)[/B]

After reading the symptoms over again and the fact that it cleared up while riding consider that maybe you experienced that rare event called bad gas. It is also possible you had something clogging up one or both injectors that finally cleared up.

Since no one has any technical documentation on the Motronic ECUs and Bosch is not forthcoming with documentation, there is a lot of speculation on forums about theory of operation. It's easy to get confused. At least one member (Roger94RT) has done a good deal of testing and gathered some definitive data on the 1150 proving it "learns" or at least adapts to changing engine input variables. He's posted the data to prove it out.

We do know that TPS voltage input is handled differently in the 2.4 and 2.2 versions of the Motronic. This comes up all the time and there is confusion here about resetting the Motronic ECU.

Only the 2.4 Motronic reset procedure includes the need to turn on the ignition and slowly twist the throttle wide open 2 or 3 times to "teach" the ECU what the open/close limit voltages are.

The 2.2 Motronic does not need this. The TPS voltage appears to be a set it and forget it deal. It should be set to 0.370 to 0.400 VDC with the throttle fully closed.

Contrary to what was posted here, twisting the throttle does not reset the ECU. A look at the schematics will tell you this. Pulling fuse number 5 however does disconnect the ECU from 12VDC and as such would discharge any volatile RAM settings stored in the ECU. You do need to wait a few moments for this to happen because the memory is capacitive and these need to "discharge".

 

[DROOT153718]

I think you are all wrong.

The bike ran fine. MUFFLER fell apart on its own due to rust.

Muffler and cat were replaced.

Bike is now quiet but pops on decel.

My first thought is the cat is not working. When the cat is working running at really hot temps, it burns any unburned gas or hydrocarbons in the exhaust. No hot cat, no burned gasses so they can find their way to the muffler, mix with oxygen and explode.

I also have a second thought depening on how the pop on decel is acting.

With throttle closed on decel, the fuel injectors should putting NO fuel into exhaust, so no popping. Just a little throttle and some fuel is entering the engine/enhaust and can pop. IF the TPS is set higher than .4 volts the fuel does not shut off on closed throttle. This can cause popping but still needs the cat to not be working.

I found this out when I surgically removed the cat from the muffler of my R1100RT. Once it was out, the bike did not run any better, the exhaust did not sound as good as it used to and I got popping on decel. Much worse if I hold the throttle open just a little on decel. I happen to like it.

Flame away.

David

 

[aapasquale]

Is there some way to test the oxygen sensor to see if it functioning properly? Is there some sort of diagnosis that will show up a misfunction or failure of that unit that can be done by BMW dealer?

Is there a test for catalytic converter as well?

Will any harm come to the bike if either O2 sensor or converter have failed?

I will run the bike over the next couple of days to empty tank and see where mileage is--was out riding today for about 40 miles and bike seems to be running very well--the popping still there and yes, when clutch is engaged, no popping--

thanks for the input-(I think I'm becoming a borderline genius)

Tony

 

[ANDYVH]

This comment was made earlier by another poster, "With throttle closed on decel, the fuel injectors should putting NO fuel into exhaust, so no popping."

Umm, no. When the throttle is closed, like at idle, the fuel injectors ARE still spraying fuel. If they weren't the engine would not be running. So, when the bike is on decel against a closed throttle, the engine is at high vacuum and is trying to get more air than the closed throttle allows, and the injectors are still spraying. But spraying very little for the higher amount of air the engine is sucking in. After enough revolutions, the fuel to air ratio finally gets high enough to ignite, randomly, and we get the pop.

 

[DROOT153718]

This comment was made earlier by another poster, "With throttle closed on decel, the fuel injectors should putting NO fuel into exhaust, so no popping."

Umm, no. When the throttle is closed, like at idle, the fuel injectors ARE still spraying fuel. If they weren't the engine would not be running. So, when the bike is on decel against a closed throttle, the engine is at high vacuum and is trying to get more air than the closed throttle allows, and the injectors are still spraying. But spraying very little for the higher amount of air the engine is sucking in. After enough revolutions, the fuel to air ratio finally gets high enough to ignite, randomly, and we get the pop.

I am the poster. Go ride the bike. Close the throttle and let the bike coast from over 2,000 rpm. Listen closely as the engine slows down somewhere around 1800 rpm the injectors will kick back in and you can hear and feel it. Most all bikes and fuel injected cars do this. This is part the reason for herkity jerkity throttle.

Sure they inject at Idle, but not on decel.

My 1100RT does it, My 1200R camhead does it and so does my Kawasaki Versys.

So does my ford 99 diesel ford truck and 99 dodge dakota.

David

 

[DROOT153718]

Is there some way to test the oxygen sensor to see if it functioning properly? Is there some sort of diagnosis that will show up a misfunction or failure of that unit that can be done by BMW dealer?

Unhook it and see if the bike runs different

Is there a test for catalytic converter as well?

Remove the o2 sensor, ride the bike if the cat is plugged it will run better. The bike will also fall off in power at the top end if its partially plugged. I know of no way to test to see if its getting hot enough.

Will any harm come to the bike if either O2 sensor or converter have failed?

No, I unhooked my o2 sensor and removed the cat. Bike ran better with out the sensor and no different with out the cat. I prefer clean air so I would not do i t again.

I will run the bike over the next couple of days to empty tank and see where mileage is--was out riding today for about 40 miles and bike seems to be running very well--the popping still there and yes, when clutch is engaged, no popping--

thanks for the input-(I think I'm becoming a borderline genius)

Tony

Enjoy your bike!

David

 

[aapasquale]

Enjoy your bike!

David

Thanks David

Will disconnect O2 sensor next time I'm under the tank (connection/disconnection is not possible without some effort) and give it a go

Tony

 

[roger 04 rt]

This comment was made earlier by another poster, "With throttle closed on decel, the fuel injectors should putting NO fuel into exhaust, so no popping."

Umm, no. When the throttle is closed, like at idle, the fuel injectors ARE still spraying fuel. If they weren't the engine would not be running. So, when the bike is on decel against a closed throttle, the engine is at high vacuum and is trying to get more air than the closed throttle allows, and the injectors are still spraying. But spraying very little for the higher amount of air the engine is sucking in. After enough revolutions, the fuel to air ratio finally gets high enough to ignite, randomly, and we get the pop.

If you're riding along, close the throttle to less than 2 degrees (idle on the 1150 is 0.32 degrees according to the Motronic, I bet the algorithm is the same for the 1100) the injectors pulse width is set to zero, no fuel is sprayed. It stays in that condition until the RPM is below 1800 RPM, then it starts spraying fuel again.

Here is a link to some tests I made: Overrun Fuel Cutoff

 

[roger 04 rt]

Is there some way to test the oxygen sensor to see if it functioning properly? Is there some sort of diagnosis that will show up a misfunction or failure of that unit that can be done by BMW dealer?

Is there a test for catalytic converter as well?

Will any harm come to the bike if either O2 sensor or converter have failed?

I will run the bike over the next couple of days to empty tank and see where mileage is--was out riding today for about 40 miles and bike seems to be running very well--the popping still there and yes, when clutch is engaged, no popping--

thanks for the input-(I think I'm becoming a borderline genius)

Tony

Tony, The only way to test the O2 sensor on an 1100 is with an oscilloscope. On an 1150 the GS-911 from Hexcode does a nice O2 sensor display. What you would do is warm up the bike, let it idle with a fan blowing some air past the engine and look for a repeating waveform that switched between 250 mV and 1.050 V (there is a 150 mV offset added to each signal). The switching rate is roughly 1 second at 250 mV followed by about a second at 1.050 V. The numbers are rough and as long as it's switching it's probably okay. They don't last forever though and tend to get slow with age.

Once you know the O2 sensor works you could take the bike to an emission testing station and get them to measure CO, HC and NOx. That would tell you how well your converter is oxidizing the exhaust.

I assume that most of the CATs on 10 - 20 year old motorcycles aren't working that well. TB

 

[oldnslow]

I also have a second thought depening on how the pop on decel is acting.

With throttle closed on decel, the fuel injectors should putting NO fuel into exhaust, so no popping. Just a little throttle and some fuel is entering the engine/enhaust and can pop. IF the TPS is set higher than .4 volts the fuel does not shut off on closed throttle. This can cause popping but still needs the cat to not be working.


David

I was hoping some one would point this out. Being a 'new guy' I didnt want to offer up technical tid bits. My K bike is good for this if I get lazy and rest my wrist on the wrist rocker when decelerating, especially down hills. The very small amount of throttle twist keeps the injectors working and the bike 'loads up' with fuel and the BOOM out the pipe! Exhaust after firing is 99% caused by fuel in the exhaust pipe exploding/burning.

 

[roger 04 rt]

The 1994 R1100S & RS both have a Motronic 2.2 according to RealOEM.com and I question their learning ability.

There is no such thing as a 1994 R1100S. Introduced in 1999 I believe. The R1100RS was introduced in 1993 as a 1994 model. They don't learn in the sense that the later Motronic devices do. I don't believe this has anything to do with fuses, or twisting throttles, or riding for 20 miles.

This is from bmbikes.co.uk web site:

BMW R1100RS
Start of Production: 1992
Ignition System: Electronic ignition, Bosch Motronic MA 2.2

BMW R1100S
Start of Production: 1998
Ignition System: Electronic ignition, Bosch Motronic MA 2.4.

The data on the Motronic is consistant with RealOEM and with BMW Parts Fiche on the MaxBMW web site.

The MA 2.2 doesn't learn or adapt, the MA 2.4 does learn and it does make changes to the fueling data.

When I offered the advice to pull fuse 5 to reset the Motronic, it was on the belief that there may be long-term adaptation on the Motronic MA 2.2. Since it is easy to perform, it seems that one can quickly check and see what happens. I'm not alone in believing the MA 2.2 can be reset. There is an interesting description of the Motronic 2.2 on Anton Largiader's web site here: Motronic 1100 Functions. It says:

After a cold start (i.e. after reconnecting the battery), the Motronic puts some of its data to a static RAM which is not erased as long as fuse #5 and the battery are ok. After a warm start, a checksum is computed to see if the RAM contents are still valid.​

The surprising thing to me about exhaust popping on any of the Motronics is that when the throttle is closed below 2 degrees and while the motorcycle is decelerating, the Motronic shuts off the injectors until the engine RPM drops below 1800 RPM--the Overrun Fuel Cutoff function. I can see a little fuel from the intake tract from wall wetting making it to the exhaust unburned for a short time but not for long. It makes me wonder if some bikes have injectors that leak in the off position, or if as someone else suggested if it's due to mis-adjustment of the TPS sensor.

Regarding Adaptation on the 1100:
I've taken enough data to satisfy myself that the Motronic MA 2.4 (1150s) is a fully adaptive fueling and spark ECU. Here are my reasons for believing it is worth exploring, with an AFR monitor like the LC-1, the adaptive capability of the Motronic MA 2.2.

--The Motronic product line was introduced by Bosch as a combination solution for fueling and spark (having built Jetronic ECUs for fueling only), with Lambda control. Adaptation is not very hard for the designers once Lambda control is included in the ECU. In 1994 when the 1100s were introduced, Closed Loop Lambda control was a 10 year old technology. (I'm reading an interesting book on Motronic written in 2001, which describes in detail the Fueling, Spark and Adaptation capabilities of the Motronic platform.)

--Every Closed Loop program that I've studied uses a short-term adaptation strategy to make it easier to lock on the correct mixture for Closed Loop fueling--the question really is whether or not it has Long Term Adaptation. It is not a big programming step to compare the Short Term Fueling Trim to the Open Loop fueling calculation. See my 1150 block diagram below. This is the basis of Long Term Adaptation.

--The value of Long Term Adaptation is that it corrects the Warm-Up Enrichment and Wide Open Throttle, and Open Loop AFRs. Without the computation of Long Term Adaptation, the WOT Open Loop AFR target, of say 13.0:1 running gasoline, would be leaned a lot to the equivalent of 13.5:1 with E10 fuel. Warm-Up enrichment would be similarly lean. Sub-performing injectors, fuel filter or fuel pressure would make that even worse. Long term adaptation would fix those problems. If one believes that the Motronic 2.2 does not adapt, then a 3.5 Bar fuel pressure regulator should be installed to compensate for E10. BMW had knowledge of the varying needs of Oxyenated fuel vs non-Oxygenated fuel in '94 so would have had a stong motivation to allow the MA 2.2 to correct for it.

--The Motronic MA 2.2 and 2.4 appear to be revision changes in the same family. Although many believe the 2.4 isnt adaptive, I've measured the Long Term Adaptive function on the MA 2.4 and know that it corrects all Open Loop fueling.

--The Motronic MA 2.2 and 2.4 use all the same input sensors, with the exception that the MA 2.2 makes allowance for one additional sensor, the CO Potentiometer. The outputs are essentially the same with the exception that the 2.4 has two outputs for Stick Coils.

For all the above reasons it wouldn't surprise me to find some amount of Adaptation on the 2.2. The most compelling reason is for the correction of WOT AFR fueling in the presence of Ethanol or oxygenated fuel.

Until someone attaches an AFR recorder to an 1100 like I've done with the 1150, it will remain difficult to know what the MA 2.2 does and doesn't do.

If someone in the greater Boston area is reading this thread and would like to experiment with the benefits on an LC-1 Wideband O2 sensor--richer mixtures, more low torque, no surging, etc., I'd be willing to help with installation. Parts cost of the project is about $200.

 

[ANDYVH]

Cool, I learned something and thanks! I was making the assumption your comment said the fuel cutout was absolute right down to idle. Actually, after reading the details I can understand the rationale for stopping fuel spray from the injectors on closed throttle decel. It correlates with methods to reduce emissions during decel, which is common practice on 4-stroke engines for almost decades now.