Every once in a while there'll be a 'bike not running' thread, and the OP will looking narrow-eyed in the direction the ECU...
I'll head for the keyboard, probably post a picture of a mashed up, highside-then-hit-a-tree K100 ECU and point out that the thing still carried on working once I'd bashed the ally casing straight again. Nope, nobody need worry about the ECU.

So after three days of troubleshooting, everything, on the Madass, turns out it was the ECU, that had gone poorly with some very weird symptoms:

Bike started & ran fine, but misfired (just like a HT/plug cap/spark plug fault) at 5500rpm. Coughing and kicking and refusing to rev any higher (no matter how much I tried, ahem).
Rode it for a while like this, thought it was the damp weather - must look at the HT leads etc.
Bike would rev to 7-8 ish if not under load - i.e. testing in the garage.
Plugs not bad, maybe a little sooty.
Exhaust gas nice and clean.
Bike would nearly rev fully out if I stuck my hand 3/4 over the AFM inlet, whilst fully opening the throttle.
Bike would do the same if I manually turned the AFM vane fully open.
(Okay, so the last couple of points suggest a weak mixture - I replaced the blocked & collapsed 30 micron fuel filter (yay I've found the fault!) and this gave NO improvement, gnash gnash gnash)

FINALLY, swapped the they-never-fail ECU and bingo.
Took the old ECU to bits and saw this....



....which is what I'd expect to see inside a thirty year old ECU - I have no idea what I'm looking at lol 

I know of one that failed.  While the K75 was sitting for years some tiny ants decided to make a home in it.

(Sorry. No pics.)

The only ones I have encountered that failed all were when water got in and they were turned on before being dried. Usually from using a pressure washer.

In my dimly-lit view of all things electronic, these kind of things tend either to work fine, or not at all. The 'let's-pretend-I'm-a-faulty-spark-plug' had me fooled, which isn't hard I suppose.

Can't even blame vibration/faulty solder joint/broken track, 'cos the thing didn't work properly even when I was nursing it in my hands.

Oh well, fixed it with a new one borrowed from the project bike. Make a good spare for anyone who doesn't ever rev things past 5k/has too many points on their licence/etc.

(Seriously, only posted this in case the symptoms help future troubleshooters )

Chris: it  sounds like you're describing a duff capacitor (or possibly resistor) in the advance curve circuit. I've not had a K ECU fail like that, but your description exactly matches a problem I had with with a Pirahna ignition system on a Guzzi 1000SP some years ago (minus the MAF bits of course!).

It's a pity you can't plug it in (on the garage bench) and power it up to try and identify the fault.

My father did this with a TV (I should have thrown out), then with the back off, got the WD40 sprayed away. Then a little crackle and wisp of smoke rose up. Loose connection found ... little bit of solder and the TV was good until i finally got rid of it. 

Don't think I've bought a TV in the last 20 years. People keep giving them away.

Then again, maybe you can give it 12V through the appropriate pins and give it a light spray (warning: I am NO electrical expert ... defer to wiser heads)

Other than that, surely it's a capacitor as Dai was pointing to

If you need one, I am pretty sure there's one in the spare box. Postage might be about 2 weeks

PM me if no joy

GF

Thanks guys. I’ve just had a close look at the capacitors and one does look as though the soldered connection might not be 100%. So thanks for heads up.
Now where’s that five hundred watt soldering iron....?

What kind of capacitor are you looking at Chris? Can we see the solder joint?

I'd imagine Dai is alluding to dried up electrolytics..?

More or less. Sometimes they just rot through the dielectric medium and short out.

can you take a pic of the underside chris ? especially around the external connector area .


don't forget that electrolytic capacitors dry out internally ...its a natural thing , with work that they get and the smaller the value the higher the percentage change in value

not hard to find to replace with standard values used commonly in bmw stuff  but I only see 1 of such in this pic , most are polyester types by the look , mostly glued down , if you had the glue, fail leg - lead fail could happen through vibration

but does sound as if its a supply issue , or possibly a rise time issue through a conditioning circuit area caused by a "dry joint "  (badly soldered or stressed solder joint )

Here's the best pic I can manage of the only suspect-looking joint I could see. It's directly top left of the upper square cutout in the board. I've scraped a little of the flux/whatever away.


It's one of the legs of this capacitor, centre picture.


Which, although the writing on it is obscured by an adjacent component, appears to be the same values as this - 2.2mf, centre picture:


The board itself seems quite twisty, either heat or age:


I don't suppose this could be the culprit (it's about the only component on there whose function I understand lol!)


Thanks for your help. A replacement arrived today from German Germany, blue label, different part number, all-metal casing. I guess it'll work on the new bitsa project. I'll definitely have a crack at fixing this one though, if you think it's worth a try.
I also started having those mad thoughts again - why wouldn't a K100 ECU work a K75?

chris846 wrote:
I also started having those mad thoughts again - why wouldn't a K100 ECU work a K75?

It may possibly because the Hall Sensor signals are at different points in the rotation of the crank(120 vs 180 degrees). 

It's possible that the airflow sensor has a slightly different door deflection based on only three cylinders pulling air in the K75.

The thought has crossed my mind as well because I see my K100 ECU through a somewhat jaundiced eye and it seems that used K75 ECU's are a lot cheaper than K100 units.

Well, Mr Point Seven Five,
I'm going to try!


The Jetronic takes its signal from the ignition module outputting a cylinder 1 firing signal, and it bank fires all three/four injectors once every engine rotation.
I'm guessing the 3-coil 75 is still wasted spark, same as the 2-coil 100, because there's no camshaft sensor on jetronic.
So, in the land of the dimwitted at least, both the triple and four jetronics output an injector pulse of a duration mainly mapped to engine revs, but also modified according to AFM. The duration of the pulse needn't be massively different between a triple or a four, 'cos each injector only serves one cylinder.

As you have said, it's the modification-according-to-AFM that could make a difference - a four will have more airflow at a given rpm than a three, so a four cylinder jetronic on a triple, will think that the throttle isn't open as much as it actually is, and maybe run things a bit leaner than they should be. Likewise a triple jetronic on a four, will think that the throttle is open wider than it is and put a bit too much fuel in.

All of which could be crudely offset with an adjustable FPR.

But why? It's seven am, and this kind of thinking is just perverse.

Mr chris846, you have motorcycles on the brain. I also find that sometimes you will wake up in the middle of the night and think about your motorcycle. It means that you need someone who will understand your situation and offer help.

As I struggled recently with my K100RS overfueling issue I began to daydream about putting a motronic in place of jetronic ECU. 

Swap the engine harness, ignition modules and ECU, replace the MAF airbox with the Motronic airbox and throttle position sensor.

It seems so simple...

Point-Seven-five wrote:As I struggled recently with my K100RS overfueling issue I began to daydream about putting a motronic in place of jetronic ECU. 

Swap the engine harness, ignition modules and ECU, replace the MAF airbox with the Motronic airbox and throttle position sensor.

It seems so simple...

Actually started buying parts to do just that some time ago... then found out the Moronic badly over-fuels the 2-valve engine in the mid-range. It's buried on here somewhere - the guy who built the JJ Cobas replica did all the research.

Ringfad became the unexpected recipient of a Moronic and cables

You'd be much better off adapting a MegaSquirt or MicroSquirt EFI to the 2-valve engine.  There is a thread over on the other K-bike forum by wmax351 which discussed that.

BSK SpeedWorks - BMW K Series Engine Management Package

Most of my bikes cost less than this, but I have seen it fitted to a racing K1

robmack wrote:You'd be much better off adapting a MegaSquirt or MicroSquirt EFI to the 2-valve engine.  There is a thread over on the other K-bike forum by wmax351 which discussed that.

Here's a description of the result. He sold it. Last time he posted, he indicated he adopted his uncle's 1998 Moto Guzzi California and was enjoying the ride.

Here is the outfit that inspected and repaired my Ign. Module in 2013 they also repair all the other Hi Tech stuff that is no longer supported by BMW...

https://www.carmo.nl/index.php?main_page=index

Hi

Did you check the flux capacitor??

DiLithium-Iron crystals is on another thread, about batteries.
Do pay attention!

chris846 wrote:Do pay attention!

No one was expecting him to go for the juggler