Testing Electonic Ignition

[wilcom]

I just ran across this post from Tom Cutter. Seemed like good stuff and I will be filling it away to use if something goes "bump in the night"


"GUIDE TO TESTING BMW AIRHEAD ELECTRONIC IGNITION

(Even if you work dog-slow, this will take less than an hour, and does not
involve buying and installing components one at a time until you stumble on
the solution like a blind squirrel finds an acorn. That isn't diagnosis, it
is the Blind Squirrel Method. Many BMW dealer mechanics rely on this method
in lieu of learning how stuff functions and how to use test equipment.)

Instructions work for ALL BMW-fitted Electronic Ignition Airheads 1981-1996:

DISCONNECT BATTERY GROUND CABLE(S)! Then Remove front engine cover.

Disconnect beancan 3-pin connector below diode board. It has a little wire
bail that is a PITA to remove. I use a hooked pick to pull one end of the
clip and the connector will release. Handle the connector carefully, old
ones often crumble in your hands. That sucks. If that starts to happen,
MARK each of the three wires as to position, and make a note of the marks.
You can insulate the three wires and connect them individually as a
makeshift.

Stick a straightened, unpainted paper clip into the CENTER female terminal
on the harness side of the connector (beancan disconnected.)

Remove ONE spark plug. Stick plug up into the cable, FIRMLY ground the
spark plug in a location where it cannot fall off and where it has good
ground. Put it so you can clearly see the spark. This test works better in
low light.

RE-connect battery, turn ON IGN switch, kill switch ON. Instrument lamps
should be ON.

COIL and WIRING TEST: Flick kill switch on and off as you watch the spark
plug. Got ONE spark each time? The coils are OK, stop suspecting them.

BEANCAN TEST: Scratch the paper clip across the alternator housing
(unpainted aluminum=good ground) like striking a match, while looking at
the spark plug:

IF you SEE spark as you scratch the paper clip across Ground, the BEANCAN
is bad - Probably failed HES. Replace beancan. Oops, BMW doesn't sell them
any more. Motorrad Elektrik and their dealers (me among others) sell a
replacement system with new beancan AND ICU, with digital advance.
Excellent for Dual Plug systems, (order the right module.)

If you DO NOT SEE spark, most likely culprit is the Ignition Control Unit
under the tank. (ICU). (By process of elimination.)

If you replace the ICU, clean off the mount carefully, get all the old heat
sink compound off, and put on new heat sink compound. DO not install
without heat sink compound. I repeat, DO NOT install the ICU without heat
sink compound. It is not optional just because you live out beyond the last
house on the left. Find some and renew the compound on the ICU every few
years. More if you ride a lot in hot conditions.

Hope that helps.

I'm sure I left something off, but this method has helped me diagnose
dozens of dead Airheads that "Nobody can find the problem".

Tom Cutter"

--
Tom Cutter
Yardley, PA
www.RubberChickenRacingGarage.com
"The liberty of man is not safe in the hands of any church."
-Robert Green Ingersoll

[BPT]

Thanks for this post, I'll copy and stick in my book for future reference.

On a related note, I was looking for a way to test the Hall sensor.  There is a now dead link that comes up everywhere that's supposed to have instructions on building a cheap, simple tester. Can't find it saved anywhere.

After my ignition problems a while ago, I decided it would be a good idea to get a spare bean can. Found one on ebay, looks to be in good shape, but I figured it'd be prudent to make sure the sensor is good.  So I was looking for a way to do that with one off the bike.

Has anyone put one of those together?

[Bob_Roller]

Here's a link to Snowbums tech site .

http://bmwmotorcycletech.info/Ignition.htm

I can post the text, but not the picture of the tester .

It's about 3/4 ths the way down the list .

[Tony Smith]

A somewhat more sophisticated version - but you could just build half of it.

[georgesgiralt]

I saved the simple tester years ago before it went lost.
Enjoy.
BTW, one can find male and female connectors easily. They are named AMP Junior timer connectors. And they are relatively cheap. (I buy mine in Germany at a shop specializing in automotive connectors)

[BPT]

Thank you, Gentlmen.
Wilcom - I'd seen that one on Snowbum's site but he had a statement there saying something to the effect of "if you don't understand this completely, don't bother".  I assumed that was written for me!    I'm good at putting things together with explicit instructions but I wasn't sure if there was a chance of frying something with his if it wasn't done correctly.

Thanks George & Tony - I can probably rig one up now that I've seen a few different ones.

The one I was talking about was supposed to be really simple, a battery, LED, and not much more.  I saw the same thing referred to a bunch of times but most of the posts were pretty old and the links went nowhere.  Couldn't find a current site that had it anywhere.

Thanks again!

[BPT]

George - after typing all that above, I just saw the name on your diagram "Frankham".  That's the one!

[Tony Smith]

The one I was talking about was supposed to be really simple, a battery, LED, and not much more. 

Thanks again!

Use a standard 9V battery connector and omit the STDP switch, omit the push button whch does nothing more than show you the LED is working and you are left with an LED and a 1k ohm resistor -does not get simpler than that.

Whilst AMP Jumior Power Timer plugs and sockets are somewhat available, they are more available in Europe than they are in Australia - I used alligator clips to connect to the beancan plug.

Please note that you can also easily test hall effects with a 9V battery and a multimeter.

[georgesgiralt]

The led should flash once per turn when you actuate the bean can rotor.
It helps to triple check that the led is working before dumping a bean can because the led is dead ;-)

[BPT]

And how is it done with the meter and battery, Tony?  You mean no resistors or LED's involved?

[Tony Smith]

The led should flash once per turn when you actuate the bean can rotor.
It helps to triple check that the led is working before dumping a bean can because the led is dead ;-)

I agree, would be a bit of an embuggerance to go to all the trouble to replace the hall effect because a $0.03 LED had gone to its maker. :-)

[Tony Smith]

And how is it done with the meter and battery, Tony?  You mean no resistors or LED's involved?

Well, at the highest the Hall effect is simply a switch that has three wires - +ve in, -ve (ground) and -s (signal or switch), they are interesting in that that relative to most semi conductors they can pass a quite respectable current.

So, connect the +ve & -ve terminals of a 9V battery to the appropriate terminals of the beancan and then connect the positive probe of your meter to "signal" and the negative probe to the -ve terminal of your battery.

Rotate the beancan and you should, after setting your meter to a suitably low range, see power on the signal pin when the hall effect triggers (or alternatively you will see power at first and then see it disappear at the 'trigger" point.

The above may seem confusing but contrary to popular belief the ICU fires the ignition on "change of state" and not necessarily on seeing voltage - this is useful as it allows the now unavailable 2AV54 to be replaced with such things as the far more readily available Siemens HKZ101 which works exactly opposite to the 2AV54. The OEM HoneyWell 2AV54 defaults to "off" and switches "on" when the cutout on the circular vane in the beancan passes, whereas the HKZ101 is default "on" and switches "off" when the cutout passes.

I may have the properties of the two devices around the wrong way, but the important thing is that the ICU couldn't give a damm and will go ahead and fire the coil on the change of state  - the timing difference between the two being a very small fraction of rotation and able to accommodated by the existing adjustment on the beancan - this is ONLY relevant if you fit something like a HKZ101 (which may no longer be necessary given that the 2AV54 is now being manufactured in China) and your carefully marked approximate timing position on the your beancan will no longer be relevant.

[BPT]

Thanks Tony. I might give that a try. Sounds simple enough reading it but I'll see what happens when I actually try to connect things.

    Thanks