No spark, part II

[MarkCBouchard]

As mentioned in this thread: http://forums.bmwmoa.org/showthread.php?t=28198
I had some problems with the connections into the ignition control unit. I thought the issue had been resolved but I was proven wrong today - no spark on the plugs no matter what I did. There is still the spark when I turn off the ignition so the coils seem to be OK. I checked all connections, sprayed the terminals with electronic cleaner, still no luck. I followed Clymer's instructions in section 6, when I got to step c) there was no voltage reading at all. So I guess the problem is with the control unit or the trigger unit.

Now, 7 a) says to pull terminal wire # 5 out of the connector - it is stuck. Is it supposed to slide gently out or do I have to use force? I didn't want to be too brutal in fear of tearing it off. Until I get it out there seems to be no telling if it's the control or trigger unit that has resigned. Or am I looking in the wrong places? Ideas anyone?

Balder

 

[MarkCBouchard]

Ok, so no ideas from you guys yet. I think I have narrowed it down to a faulty ignition trigger unit. Is there any way I can check its function? I found instructions on how to disassemble it here :

http://www.deathstar.org/~flash/ig_trig.html

but I don't want to start tearing it apart before I know for sure that this is the culprit. Ideas anybody?

Balder

 

[20774]

I don't have much experience with the electronic ignition systems of the '81-on bikes. But this sort of thing comes up on the Airheads.org forum. I recall Tom Cutter has posted diagnostic steps to isolate a problem with no spark. I found one of those posts and have included it below. Look this over and see if this might help with finding the problem. Tom provided this for a person who was having trouble with an '82 R100.

Tom posted:

"There are three compoents to the electronic ignition system: the trigger unit, aslo known colloquially as the beancan, the ignition amplifier, and the coil. The coil supplies spark to the plugs via the secondary wires and the suppressor caps.

Now you need to isolate whether the two remaining items, the trigger unit or the amplifier, is at fault. There is a real simple roadside diagnostic trick to use to determine which of these items has gone bad. You will need a small, uncoated (non-colored) paper clip or similar piece of stiff wire abut three inches long. Leave the plugs out, but installed into the suppressor caps and firmly grounded on the cylinder head fins. I use a bungee cord around each head to make sure he plugs stay put.

You need to remove the front engine cover, which requires disconecting ALL ground connections at the battery.

Once the cover is off, find the plastic connector from the ignition trigger unit. It will be tie-wrapped to the web in the casting right under the diode board. Cut the tie-wrap and gently pull the cable toward you so you can see the square C-shaped clip that holds the conector together. Use a hook to pull the short ends of the clip away and off the connector until you can remove it entirely, which will allow you to unplug the connection.

Now take the straigntened paper clip from the step above, and insert the clip carefully into the CENTER female connector on the wiring-harness side of the connector. That will be the end NOT attached to the beancan. For practice, try stroking the end of the clip against the unpainted aluminum of the stator housing like striking a kitchen match. Now temporarily secure the clip AWAY from any metal surface, and reconnect the battery ground cables. You can use an alligator clip for this, because you will need to remove the connection again to reinstall the front engine cover.

With the battery conected, switch ON the ignition and kill switches. Watch the spark plugs for spark, as you strike the paper clip across the stator housing as if striking the match. The spark plug should fies repeatedly as you scratch the clip across the metal.

If the plug fires, the Ignition Canister is bad. The canister is the home for the Hall trigger unit. You can get these rebuilt by Oak or by Motorrad Elektrik. M.E. also offers an exchange service forrebuilt units. If you are a real handy repairman, you can replace the Hall sensor yourself. There is a well-written article on the subject on the internet, but I am away from my home computer where I have that link stored. I coul dnot find it with a quick Google search. If somebody else doesn' tpost the URL to the article, I'll try to remember to do it when I get home Sunday evening. Often, the real problem is NOT the Hall sender unit itself, but the cheesy wires from the Hall unit to the connector. These wires use poor insulation that is prone to cracking, which can allow moisture to enter the wires and round out he ignition signal. An easy, test for this condition is to spray the wire with WD-40, which is a good water-displacing cleaner. If you get spark when you spray the wires, then yopu need to renew the wires to the unit. Again, there is a good internet article on the subject.


If there is NO spark in this test, the Amplifier is bad. Check the condition of the wiring harness to the ignition control unit or amplifier. The amplifier module needs to be mounted with special heat-sink paste to the mount plate. If the heat-sink paste dries up, which is becoming a common occurrence, the function of the amplifier will be compromised. eplacement amplifiers are available from BMW dealers, from Motorrad Elektrik, and I am sure that Ted Porter will chime in that he sells them. So do I and many other independet MW Airhead shops. The point is that the unit is readily available. Get the heat-sink paste at RAdio Shack. Ask for HEAT SINK PASTE. The tube is tiny, but will last a million years."

 

[James.A]

Generally speaking, individual wire ends are fitted into combination connectors by pushing the individual wire ends into the housing until they seat with a click. You might try fishing around inside the housing with a very small flat screwdriver to release the wire end connector from the retainer in the slot where it resides. The flat side of the spade connector has a tiny slot that intersects with a nub in the slot of the plastic housing. Or pehaps a small punch out that forms a spring like leaf that drops over a tiny ledge cast into the slot of the plastic housing

 

[MarkCBouchard]

Thanks for your inputs. I had already performed the procedure described by 20774/Tom. There are sparks so this is my reason for suspecting that I have a faulty trigger unit/beancan on my hands. I'm still trying to find a way to check it, I guess I'll take it to a workshop and have it tested on Monday.

Balder