Thursday, July 31, 2008

The Joys of Problem Diagnosis on an Airhead Motorcycle

So, for the last three weeks or so, I had been experiencing following symptoms on Brigitta, my 1987 R80 Beemer Airhead motorcycle.

1. After about 25-30 of riding, she'd cut out on me while slowing down to a stop light, she would however restart right away. This would not happen initially during the morning commute but did occur at least once on the afternoon commute, so I thought perhaps it was the hot weather. This behavior got worse, occurring recently during the morning commute as well when its cool.

2. When riding in the rain, she would not hold idle when at a stop, I'd have to keep revving the throttle to keep it going.

3. In conjunction with #1 above, she'd also sputter/surge on me at low revs, which is rather unnerving when leaned over on a curve or starting off from a stop with a cager behind me. This was the most annoying of all.

4. Once the engine warmed, the tachometer needle would get bouncy and twitchy, specially when my revs were below 4000 rpm. I had checked all visible/reachable electrical connectors and grounding points and all seemed clean and secure.

Here's my sequence of troubleshooting that I've been following in the last couple of weeks or so.

Since I thought it was a hot weather related issue at first, I thought something was getting heated up and sticking, causing fuel flow issues at the carburetors.

a. Checked out gas flow, they flowed fine, checked right after getting home with the engine still hot.

b. Replaced the spark plugs as part of her 64k services. Replaced the oil and oil filter/transmission/final drive/drive shaft fluids as well.

c. Checked the floats in the carburetor bowls and float tested one, it seemed fine. Didn't do the other one since the mounting post was broken off at the top and I didn't want to dink with it until I safety-wire it or something first. However, both floats cut off fuel at the right level.

After much reading on the airhead forums I frequent and much counseling/guidance from one of the Gurus of the Airhead community: Snowbum, aka Robert Fleischer, he walked me through, with a series of emails through the following diagnostics:

Preface: He said my descriptions of the symptoms pointed to three possibilities:

***The ignition modules can be damaged permanently from too many cycles of 'cutting out from overheating'. NOTE that cutting out is also possible from damage to the Hall element in the ignition canister. It is not always easy to determine which part is the problem....this is particularly so when the engine will restart immediately.
USUALLY when either electrical part overheats, the engine will not restart until it has cooled-off some. Thus, I am a bit suspicious about YOUR bike. Your 1987 R80 probably has the SINGLE, dual output, ignition coil. Those coils have been known to fail. They have enough current in the primary winding that does heat them a bit in normal operation....and your problem occurs after some riding minutes. I would inspect that coil visually. In particular, if it has a GRAY body, it is suspect.
Look for cracks in the plastic housing, that was the typical visual appearance on failed gray bodied ignition coils.
Thus, whilst I DO suspect an ignition problem in your bike, it could be three things!

Armed with the above guidance, I took the tank off Brigitta yesterday and with a bright flashlight looked at the ignition coil while it was mounted on the bike. Saw nothing that looked like cracks (more on this visual inspection later). All the connections looked good. I did unmount the ignition control module and apply some heat sink compound on it before mounting it back up since I had the tank off anyways.

I reported back to Snowbum that no cracks seemed evident and he then suggested using a multimeter to check the OHM resistance values on the unit.

This is how I had the coil looking on the first ohm meter test, this is wrong

I tried my first ohm meter measurement with one of the battery wires still attached, big mistake, which caused bad reading which I sent to Snowbum:

Hi Bob, I placed the leads from the ohmmeter on the terminals which I assume lead to the battery. I disconnected the black wire from the starboard terminal before doing the reading since the clymer manual said to disconnect it. (it also gave me a reading of 15.4-15.6 with the wire hooked up so it was reading the battery probably)
I got a reading of .011, which is way outside of what the manual says I should get which is 0.67 - 0.77, am I right to assume the coil is toast? See attached photo, I placed the leads in the red circled areas, the one to the right is behind the heat sink/shield. Note, I did not disconnect the port side terminal wire, should I have?

I got this information over two emails:

***Measure the coil primary and secondaries with an ohmmeter. The first indication of a failed gray coil IS TYPICALLY a problem in riding in the rain, or, high humidity. That may NOT be your eyeball the coil very carefully for cracks, and use an ohmmeter on it. Coil or ignition wire failures can cause real idling problems, yes.

The Airheads with ONE coil, that coil having two towers on it, is usually called a 'dual coil', confusingly. It has a primary resistance of a nominal 1.15-1.32 ohms. There are some later ones with somewhat lower resistance, but certainly NOT 0.011 ohms. Its secondary is 7500 to 9150 ohms. You measure that between the two towers, down deep inside them. Be sure to measure that secondary, as it is usually the secondary that opens.

The wires should have NO POWER on them with the ignition OFF!!! Disconnect both primary wires, these are the two spade terminals.

Put the ohmmeter on the lowest range, if it has adjustable ranges. Short the two ohmmeter leads together. If you have a knob to zero the ohmmeter electrically, do that with leads shorted, otherwise read the ohmmeter with leads shorted. Subtract any reading above zero from the reading between the two coil spade terminals.

I have no idea about your 0.011...that has to be wrong...meter, or? There should be near infinite ohms readings from any of the 4 terminals to the chassis ground.

Note, I had been using the Clymer manual up to this point and their stated values for a good coil differed from the above, I now know to go with Snowbum on this.

So, when you do it you have to disconnect both spade terminal connectors! I had just unhooked one since the other was a PITA to get to without unmounting the unit which at this point I was not ready to do. Because I did not, I got a bad reading of 0.011 ohms which I sent to Snowbum.

So I dismount the coil finally, should have done that in the first place! Using my multimeter, I got a 0.2 reading when shorting the leads so I subtracted that from the 1.4 reading I got when measuring the primary resistance between the two spade terminals. Had I been paying attention the the above information from Snowbum, I would have realized that it fell within the parameters Snowbum had specified! Foolish me. I however could not get a ohms resistance reading off the secondary resistance connectors! Struggled with that for a bit, then had to go in to work, reported my failure to Snowbum via email.

So, the next morning, I took Maria over to Pete Homan's shop to return the windshield that came with Brigitta since I was not using it for some money. I brought along the ignition coil and showed it to him.

Now, here's the DOH! moment. Apparently, there were, obvious (to him) cracks all along the casing of the coil Once he pointed them out to me, they were obvious to me as well. I had mistaken the cracks to be just scratches on the casing. He also tried to measure the secondary resistance setting between the two "towers" where the spark plug cables plug in. He also was unsuccessful, had him scratching his head saying he'd never seen a coil fail in that way before. I felt better at my own diagnostic results at this point.

those faint greenish/gray diagonal lines are actually cracks

So, I bought a new Bosch Coil from Pete, using the cash he'd given me for the windshield as credit so it only cost me $86 and change.

I got both coils back home and took some comparison pictures so you can see the difference between the old coil and the new coil:

old coil on the left

p/n for the new coil, old one had 200 as last three numbers, all others the same

New Coil, mounted

I took a 15 mile or so test ride tonight and Brigitta rode beautifully. Not a sputter was felt, the tachometer was nice and steady, no surging, no cutting out when coming to a stop or otherwise. So, initially results from the coil replacement look good. We'll see in the next few days of riding, the weather is supposed to be a scorcher for the Front Range.

I'd like to express my thanks to the people who contribute to the riding forums I frequented with what turned out to be mostly solid advice and pointers in terms of diagnosing this issue. But mainly I'd like to thank Snowbum who took the time to help me via email and pointed me finally in the right direction in terms of diagnosis and confirmation of such. Thanks Bob!

LINK to Snowbum's Wealth of Wrenching Information on Airheads. If you own an Airhead, you need to become familiar with his site!

02AUG08 - The R80 continues to run great with the new coil. However, it was brought to my attention by MarkDS that BMW had also updated the Ignition Control Unit the same time they updated the Ignition Coil to deal with the cracking problem. Based on some more research, it appears that the old ICUs weren't design to handle the current draw of the new coils and after a while would start giving problems. See below links for more info.

LINK1 (you've got to join Airheads List first) By OAK, well known Guru in the Airhead community.
LINK2 by Anton Largardier who runs a nice tech info site as well.
LINK3 search results on "Failure Mode of Ignition Module" on Airheads List Archives

06AUG08 Update:
I got a new Ignition Control Module (ICM) aka Ignition Control Unit (ICU) from Their p/n 9604 is, according to them, a direct replacement for BMW p/n 12 14 2 325 284 which is the one recommended for use with the newer coils by the Beemer dealer. The dealer wanted $139, the ICM from rockypoint was $24.95. I'll keep the old stock one with the white lettering as a "spare".

old ICM on left, new ICM on right

New ICM installed, with heat sink compound of course!

1 comment:

26jbg said...

My Clymer manual (page 438) has same spec for dual coils as quoted by Snowbum: 7500 to 9150. J