Hypothetical stick coil question

Discussion in 'GS Boxers' started by pcwirepro, Oct 1, 2012.

  1. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    I have been accused of having it.

    Two new coils in. Noticeable difference but not the breakthrough I was looking for. The front tire has yet to leave the ground. So..... What's next? More tuning or a 1200?
    #21
  2. Beezer

    Beezer Long timer

    Joined:
    Oct 26, 2004
    Oddometer:
    6,767
    Location:
    Anchorage, formerly Spenard (hub of the universe)
    if (when?) it happened to mine I would just jump off the bridge..... buy the easy to get, available at any car parts store Ford coils and just cut & terminate the original BMW harness onto the new coils with readily avalable high quality terminals. why dick around? are you thinking that some day you are going to put the "tumors" back in after the operation? done in a day with common parts that are easy to find
    #22
  3. def

    def Ginger th wonder dog

    Joined:
    Feb 28, 2004
    Oddometer:
    13,572
    Location:
    The woods and mountains of Alabama
    While I am not the owner of a stick coil vehicle of any kind, I'm inclined to think BMW made some errors in the design for the Coil on Plug system. I assume that these stick coils fail due to excessive heat (and cooling) and embrittled plastic especially when one attempts to remove one for say valve lash service, and in doing so, cracks the insulation or housing by just handling the thing.

    So, sooner or later (nobody really knows) you'll need to replace one or more of these stick coils when they are least accessible (riding in some remote area with no cell service or no UPS delivery service).

    At the ridiculous prices charged for these things and their rate of failure, I would certainly entertain Hackymoto's Ford option.

    Removing the coil from the heat of an air cooled engine seems like a good idea. Replacing it with one at 1/3 the cost is really appealing. Replacing it with one that is available from a local auto parts store?...you get the idea.
    #23
  4. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    I'll see how this fresh set holds up. They have a build date of 12/11 so hopefully they have made some improvements.
    I know from experience that the machine will run on the secondaries just fine so getting stranded isn't much of a concern for us dual spark users anyway.

    I should be on a newer 1200 by the time these fail so I'll have other problems to deal with.
    #24
  5. def

    def Ginger th wonder dog

    Joined:
    Feb 28, 2004
    Oddometer:
    13,572
    Location:
    The woods and mountains of Alabama
    Looking at Hacky's photos, I see the Ford coil is much larger in diameter than the BMW stick it replaces. Well, that tells me that the Ford piece has better performance inasmuch as the number and density of the wire turns in the Ford coil are optimized, likely producing a hotter spark especially under high compression circumstances.

    Someone with the correct test equipment could determine this but, ignition coils rely on current induced as the field moves across the turns in the coil. The more turns exposed to the collapsing field means more current. So turns position and turns ratio determine the current and voltage produced by the coil. My vote says the Ford coil is better for the job than the BMW coil, even a new one.
    #25
  6. scooteraug02

    scooteraug02 Dog Rancher

    Joined:
    Feb 18, 2003
    Oddometer:
    4,555
    Location:
    Atlanta, GA
  7. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    Hacky didn't report any real gains in performance. The spark from my new OVERPRICED spark plugs does look pretty anemic. Hmmm. should I have checked the gap on the plugs from the dealer? Do you adjust those things. I better check thaty our.
    #27
  8. def

    def Ginger th wonder dog

    Joined:
    Feb 28, 2004
    Oddometer:
    13,572
    Location:
    The woods and mountains of Alabama
    Some plugs have ground electrodes that allow the gap to be adjusted. Many of the NGKs used in the boxer are not adjustable. Once the NGK gap is opened by normal wear, the plug needs to be replaced.

    My single spark boxer is fitted with Autolite 3923s. They have 40,000+ miles on them and get the occasional adjustment to 0.035" gap.
    #28
  9. the smudger

    the smudger n00b

    Joined:
    Oct 2, 2012
    Oddometer:
    3
    Location:
    Wiltshire, England
    This might help.

    Twin spark was designed to clean up emissions. If the o2 sensor sees a rise in HC's (Hydrocarbons, unburnt fuel) the Engine control unit fires the secondary, up to 60 degrees ATDC.

    An easy test is to let the bike idle, disconnect the secondary coil (the lower one) on each side one at a time. If the engine stalls then the problem is the Primary coil on that side.

    They fail quite regularly but are difficult to pick up on because if the primary fails, the o2 sensor see's a raise in HC's, then fires off the secondary. It is quite usual for a primary coil to fail and the rider be completely unaware until its ridden hard.

    When ridden fast (high engine speed) usually a misfire or 'holding back' is experienced. This is because the engine is spinning so fast that the engine controller cannot fire the secondary quickly enough to counter the failed primary.

    There, that makes sense doesn't it.....:D
    #29
  10. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    My twin spark ran fine at idle and did quite well at high speed and even on uphill canyon runs. There were just times that I thought it was lacking something. So yes, I agree that a rider could be completely unaware of a failure. On a dual spark boxer that is.
    #30
  11. def

    def Ginger th wonder dog

    Joined:
    Feb 28, 2004
    Oddometer:
    13,572
    Location:
    The woods and mountains of Alabama
    While I don't disagree with you, I do think this sounds like a Mickey-Mouse way to fire an engine, especially if the primary ignition system is junk to begin with.
    #31
  12. roger 04 rt

    roger 04 rt Long timer

    Joined:
    Nov 9, 2011
    Oddometer:
    2,712
    Location:
    Massachusetts
    Your comments that the primary and secondary plugs fire at different times is interesting. I haven't read this idea elsewhere and haven't seen signs that it happens in the GS-911 data that I've been collecting. I'm not disagreeing but would like some more info. Here is some spark data I took last month.

    [​IMG]

    While I can believe that the Motronic might somehow use the O2 measurements to affect spark timing on the secondary plugs, I've seen no signs of that and haven't read elsewhere that it happens like you say. And on a technical note, the O2 sensor has no ability to measure unburned hydrocarbons. The O2 sensor's output voltage stays near 800 mV until it senses oxygen in the exhaust (lean mixture) at which time the voltage drops to about 100 mV. It stays at 100 mV until the oxygen is gone (stoic or richer). It is only an oxygen sensor not a hydrocarbon sensor.
    #32
  13. eric2

    eric2 ®egister this:

    Joined:
    Aug 13, 2003
    Oddometer:
    3,866
    Location:
    Austin
    Actually the twin spark was first used on the 1150s to address persistent surging. The 1200s carried this forward AND incorporated dual o2 sensors to increase sampling, which fixed the surging problems. Cataclysmic converters handle excess emissions.

    I guess you could break one if you're a klutz while replacing plugs or adjusting valves but I haven't heard anyone admit
    it.

    Like I said, mine lasted 120k miles. I would use a ford coil but i'm not going to hack on the wiring to make it fit. Some enterprising soul will make a mint selling bolt on replacements at half the cost of the bmw oem parts.

    Finally, when mine went out it wasn't undriveable, it missed under load pretty bad but I could have ridden it for a while.
    #33
  14. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    I still don't see how the motor can run as well as it did on the secondary. Where is that thing in the cylinder? Near the bottom? Also, if the primary was not firing would the compute have leaned out or enriched the mixture to compensate?
    #34
  15. SR1

    SR1 Back in S. Korea

    Joined:
    Apr 6, 2006
    Oddometer:
    4,797
    Location:
    Seoul Survivor
    PCI,
    I'm sure my experience isn't endimic of ALL coil issues, but I think it was pretty standard. The bike would idle "fine" and would putt around at parking lot speeds without any negative indication. In fact, even two BMW mechanics rode the bike and found no problem. I guess they rode like Grandma because as soon as I got back on the bike it nearly threw me off with all the bucking. Another rider at that BMW shop, an amateur racer, took it out and immediately came back with "yeah, it's shit."

    In other words, at least in my experience, I could take both primaries out and the bike would idle. I could take any 3 coils out and it would idle a little. I could ride around on any 2 coils. But under load, even up to all 4 coils, it would buck strongly, as if someone was hitting my kill switch over and over while I was accelerating.

    A coil later (though I replaced basically all in my troubleshooting) and it was as good as new. (I guess I have plenty of spares, right)?

    You are kind of going down the rabbit hold of "why coils suck" which happened a little in my thread too. Perhaps in your case, you should ride someone else's 1150 and see if it performs the same way?
    #35
  16. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    I'm sure you're right.
    #36
  17. roger 04 rt

    roger 04 rt Long timer

    Joined:
    Nov 9, 2011
    Oddometer:
    2,712
    Location:
    Massachusetts
    I guess it runs as well as it does on one plug because the air-fuel charge is getting ignited. Relative the the piston, its sitting at the side of the chamber. On my plane which had dual mags and plugs, shutting off half the plugs didn't due much but result in a drop in rpm.

    If it didn't misfire the Motronic won't do much that's different. If it does misfire, there will be lots of oxygen in the exhaust since the fuel didn't burn which will lead to the Motronic adding fuel. Eventually it is likely to burn in the catalytic converter, making it very hot and possibly damaging it. Happened on my '02 Xterra after some squirrels ate a plug lead.
    #37
  18. pcwirepro

    pcwirepro Aspiring Adventurer

    Joined:
    Aug 2, 2012
    Oddometer:
    282
    Location:
    State of confusion
    I got the bike out on longer high speed run and it does run much better with both primaries. There's a lot more throttle available in gears 4-6 and the bike doesn't have the same buzz or vibration it had before. Still some but nothing like before. Hopefully no permanent damage was done by running it like with one primary down for as long as I did.
    #38