Hypothetical stick coil question

[def]

Originally Posted by the smudger

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.....

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.

[roger 04 rt]

Originally Posted by the smudger

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.....

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.



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.

[eric2]

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.

[pcwirepro]

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?

[SR1]

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?

[pcwirepro]

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?

I'm sure you're right.

[roger 04 rt]

Originally Posted by pcwirepro

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?

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.

[pcwirepro]

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.