1995 R100RT Classic - Sudden engine cutoff

Discussion in 'Airheads' started by Muravey, Aug 14, 2019.

  1. UnclePete

    UnclePete Been here awhile Supporter

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    I'll ask here .
    Recently I bought a beancan on ebay , to repair and have a spare .
    Along with it came an unused sensor in a baggie . 2AV54 , number below that 9104 , no brand .
    Can anyone confirm that 2AV54 is the correct sensor ?
    #21
  2. Muravey

    Muravey Folk you.

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    According to Snowbum and to what I can gather from my own two-week-long Google-hunting, the Honeywell 2AV54 is the correct sensor:

    Click here for a link to the source material
    .
    #22
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  3. Muravey

    Muravey Folk you.

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    So last week I located and bought a replacement sensor for my bean can. A friend who works in the automotive industry pointed that the Hüco-Hitachi HC138154 has the same physical and electrical characteristics as the original:

    IMG_20190820_165230.jpg IMG_20190820_165512.jpg IMG_20190820_165524.jpg

    To whom it may concern, here is a list of equivalent sensors:
    • Volvo 1346792-3
    • Hüco 138152
    • Facet 8.2722
    • Bremi 16522
    • Intermotor 14011
    • Vemo V95-72-0038
    I refurbished the bean can while I was at it. No major problems, just cleaned everything and re-lubed the moving parts. Replaced the worn sponge gasket on the bean can's lid with a DIY piece made out of cork:

    IMG_20190821_184432.jpg

    The tricky bit is riveting the new sensor to the ignition plate, which is easier if you've got a friend to hold the pieces together on a hard surface while you strike the rivet with a punch and hammer. Unfortunately, no pictures of that.

    Mounted the can back on the engine, swore heartily at the connector's wire clip and proceeded to start the bike. I got spark, but a weak one. Bike did start, but would cut off spark at anything above tick-over rpm. Bummer. So it wasn't the bean can after all. Not mad at the hassle of replacing the sensor, at least I've got a new one that should last me quite a long while.

    But I did have to go back to the "drawing board" and to the original suspicion of the coil and / or ICU.

    In the meantime, a week has passed and I've rechecked the list of compatible parts available on the market for the ICU and coil. Got myself a Mobiletron IG-H004H ignition module and a Bremi 11899 ignition coil (0.5 ohms in the primary winding and a rather low 7.18 Kohms in the secondary - at least compared to the original's 12.8 Kohms):

    mobiletron_bremi.jpg

    The new coil's square metal bracket seems very similar in size to the original Bosch unit, so mating the new coil to the old mounting bracket on the bike may prove easier than expected. I will probably get to the bike tomorrow and will let you know if I solve the problem by replacing these parts.

    However, I'm puzzled by the ICU connector on the bike's wiring. Is it supposed to have a missing pin at the very end? Check this out:

    IMG_20190815_180613 (2).jpg

    As far as I can tell from wiring pictures pertaining to these modules, that pin connects the ICU to a supposed electronic tachometer. I know that the bike's got a mechanical tach, but is it ok to be missing? Do your connectors look the same?

    215078.jpg
    #23
  4. bmwrench

    bmwrench Long timer

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    Siebenrock and others sell a new plate complete with the Hall Sensor. It's not cheap. but so much easier.

    I have a couple of empty been cans if anyone else has super-strong fingers :)
    #24
  5. Warin

    Warin Retired

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    Short version: don't worry about the extra pin.

    Most of the electronic tachos take there signals from the coil primary. This means they can work with a points system or and electronic ignition system. All airhead electronic tachos all use the coil - they don't connect to that special pin on the ICU so bm save a few cents by using an ICU without the pin. An ICU with that pin will still work even if there is nothing connected to that pin.
    #25
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  6. Muravey

    Muravey Folk you.

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    Update: so I'm sitting on my butt next to the bike right now. Just replaced the coil and the ICU. Already replaced the sensor the bean can last week.

    Still the same. Starts, but dies at anything above idle.

    BUT I just noticed something odd: the engine dies out from total loss of spark the exact moment when the generator light extinguishes. Any thoughts on this?

    Have I got some sort of weird short in the charging system that affects my ignition?
    #26
  7. UnclePete

    UnclePete Been here awhile Supporter

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    …..Starts, but dies at anything above idle …
    Many years ago I had a truck that started doing that . It would start easily , but die as soon as I tried to rev it up .
    I lucked out , because the coil was in plain view , and what caught my eye is that the wire from distributor to coil was attached with about 2 or 3 strands ; the rest of them broken .
    I suppose you will need to inspect your wiring and clean and check connectors . Something may have been pinched , but is not now , or rubbed through , but not visible .
    Curious to know what you will find .
    #27
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  8. Muravey

    Muravey Folk you.

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    Thanks for the advice, Pete! Coil and / or coil wiring was my first guess too. However, the wires and connectors under the tank look spotless. I haven't found anything suspicious in the connectors to the coil's primary winding. Yanked on them a little and flushed them out with contact cleaner, just in case. Will run them through a multimeter next chance I get. Gonna keep at it in the following days.

    Yeah, I'm pretty much certain of it at this point; especially since replacing the ignition components didn't change anything (got spare parts now though, so not bummed about it). Some insulation must've gotten pinched somewhere.

    Here's how the bike behaves at the moment:



    Is there a less-than-obvious reason for which the charging system might affect ignition like this?

    I must admit I haven't changed neither the spark plugs, nor the plug caps or HT leads. Felt like the problem must definitely be elsewhere. But I just came across this old post from 2016 and it's got me thinking:

    #28
  9. ccmickelson

    ccmickelson MonoMania Supporter

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    That's a weird one. The timing sounds way off. Seems a number of things not right there.
    #29
  10. Muravey

    Muravey Folk you.

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    Most likely it is. Haven't had a chance to set it properly after rebuilding the bean can. In the video, I set it by hand to keep the engine from idling above charging rate.
    #30
  11. ME 109

    ME 109 Long timer

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    When your bike is idling same as in the video, pull the choke on as you slowly open the throttle.
    Let's see if it's fuel or spark.

    I think there was one problem with the engine cutting out as in your first post, and now there's another issue.
    #31
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  12. Muravey

    Muravey Folk you.

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    Thank you for the suggestion, I already tried it and it's the same: bike dies above idle, just as the gen light goes out.

    Will film it next time and post it here.

    As for the problem being caused by something else now, there has indeed been a difference since replacing the sensor: bike can no longer rev above idle, no matter that. With the old sensor, I could get a few seconds of revs before sputtering and cutting off (video of this a few posts back). Replacing the coil and ICU had no effect.
    #32
  13. durtwurm

    durtwurm Talented Amateur

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    My advice? You've tried a lot and are still stuck. I'd find a real BMW airhead mechanic and have him take a look see. I think he will find the issue in short order. Someone that works on these rides all the time "see" them in a way you or I do not. Yes, I know they cost money but I'd consider it.
    #33
  14. Muravey

    Muravey Folk you.

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    [​IMG]
    #34
  15. 100RT

    100RT Long timer

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    I just read this on Snowbums site. Who knows, its worth a look.

    " A rare, but super-annoying problem, because you likely will go bonkers before you find the answer, is a 1981 & later electronic ignition Airhead, that typically will idle OK, but won't raise rpm up properly. This problem acts somewhat similarly to a hole in the carburetor diaphragms. The actual problem may be a poor ignition kill switch at the bars. Cleaning that switch may not fix the problem. Bypassing the switch will show whether or not the problem is that switch. "
    #35
  16. Muravey

    Muravey Folk you.

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    Thanks for the tip! I stumbled upon the same bit of information last night. Bypassing the kill-switch with a screwdriver across the two solder points behind the switch itself was one of the first things I did.

    But who knows? I did on the side of the road. I'll try again next chance I get. Can't hurt to rule it out while troubleshooting in peace and quiet.

    Also, I'm headed for some fresh plug caps and HT wire tomorrow.

    In the meantime, can you spot three diligent helpers in this photo?

    IMG_20190831_164151.jpg
    #36
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  17. Uke

    Uke visualist Super Supporter

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    Do they wake up long enough to follow the shadow? :-)

    #37
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  18. 100RT

    100RT Long timer

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    I'm still running the original wires on my 81 R100RT I cut the caps off and found one had a burned thru resistor. I bought NGK LB05F caps and screwed them on the wire ends and been fine. Just turned 175K.
    https://www.ngk.com/product.aspx?zpid=20068
    #38
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  19. Muravey

    Muravey Folk you.

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    They are a wonder of self-preservation, yes.

    Thanks for this idea! And congrats on a long-lived engine. :)

    What symptoms did your bike show? Trying to piece things together...

    Edit: I just discovered this old thread from 2015 that belongs to Ola A. The man faced pretty much the same problem:

    Apparently, he removed the gen light for testing purposes and the problem disappeared while the alternator wasn't charging. I will test the same thing first chance I get. Unfortunately, Ola's thread ends abruptly after some testing with a second battery hooked up directly to the coil. Kindly asking @Warin if he knows more about the end result.
    #39
  20. Ola A

    Ola A Adventurer

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    Hello :-)
    Yes I also experienced that the motorcycle died. I could only run the engine until it started to charge. Took me home 100km in 40km / h.
    It turned out that the ignition hallsensor stopped working when the generator started charging. Probably because of the magnetic field. I ordered a new sensor from
    http://www.hallsensors.de/Hall-Vane.htm
    http://www.hallsensors.de/CYHME56C.pdf
    You can read about it here.
    http://www.bmwklubben.se/forum/viewtopic.php?f=220&t=23644&p=180385&hilit=halleffekt#p184357
    At first I tried with CYHME56 but it was also too sensitive to the magnetic field. I then tried with CYHME56C which worked perfectly. It is less sensitive to magnetic fields. As you can see from the pictures I mounted the sensor in a slightly different way with M2.5 screw. Since then, the motorcycle has gone very well and several thousand km.
    You can also find more information here:
    http://www.bmwklubben.se/forum/viewtopic.php?f=220&t=8211&p=184358&hilit=CYHME56C#p184358

    Another motorcycle friend had the same problem. He first bought original parts. These turned out not to work and to be defective. He then acquired CYHME56C and had a workshop replace the original hallsensor. After that, the motorcycle worked perfectly again.

    Since it is some work to replace the sensor and at the same time a lot of mechanics in the beancan, I would probably recommend to replace the original ignition with new electronic.

    Hope this helps you. If you want to hear from me, I will try to answer your questions.
    Sincerely
    Ola Abrahamsson, Sweden
    #40
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