coils

[peterleo]

Both of my primary "coil over plug" coils quit on me a while ago at 42500 miles on my 04 R1150R. The bike had just had a dealer service at 42k where nothing was noted to be out of the ordinary despite me mentioning that the bike had experienced some hard starting and high rpm hesitation. Obviously something cooked the plugs but I can't figure out what and was wondering if anyone on the forum might have any ideas. The bike has been running great the last 1000 miles or so with the new coils in place I would just like to prevent this from happening again if I can.

Thanks

[Dave_Faria]

Do u still have ur old coils?? I plan on doing an autopsy on mine with a dremel tool. I want to know why I can't read a resistance between what I think are the secondary coil connections.

Dave Faria
Austin, Tx

[peterleo]

I too try'ed getting a resistance reading from mine but got nothing.

[Dave_Faria]

Pete I looked at my coil last night and it is epoxy filled so a dremel would do me no good. I don't have a band saw so I can't do a cross section. The last thing I tried was a web search. What I found was a Denso drawing of a stick coil but, no circuit. I did also find one promising web site that talked abt the BMW Motorcycle ignition. I could not open the web site because for some reason it allows only so much "Free access". I was told to try bk at the beginning of next month.

[peterleo]

I measured mine across the pins with small aligator clip and an OHM meter and found no resistance then I threw the old ones away.l have been told by a couple of dealerships now that this is not an uncommon problem. I just wonder what could be causing it.............................Tkm

[deilenberger]

I measured mine across the pins with small aligator clip and an OHM meter and found no resistance then I threw the old ones away.l have been told by a couple of dealerships now that this is not an uncommon problem. I just wonder what could be causing it.............................TkmCrappy coils is what causes it.. it's quite common on the BMW car side, enough so that they've given an 8 year unlimited miles extension for the coils on the warranty on the two BMW cages I own. Both the cars have had all 6 coils replaced at least once (one had an individual one replaced, then all 6..)

Hopefully the latest versions are a bit more reliable (getting 40kV+ out of a coil that small - reliably - has got to be a challenge..)

[Dave_Faria]

The new coil I got also showed an open across what I think are the secondary contacts. That's why I was trying to find schematic of the BMW coil or a coil. The location I tried to measure a secondary resistance was between the spark plug cap and the center pin on the connection plug. The outer pins on the plug seemed to be the primary - both measured 1.2 ohms.

A few years ago I had several bad ignition modules on a 1993 Jimmy. What I found was a corroded ground at the ignition coil. It would actually blow a small hole in the module that would drive the ignition coil - distribitor type system. It would continue to run but, lose low rpm power, I wonder how our systems are grounded - thru the ECM or a ground lug somewhere.

[deilenberger]

The new coil I got also showed an open across what I think are the secondary contacts. That's why I was trying to find schematic of the BMW coil or a coil. The location I tried to measure a secondary resistance was between the spark plug cap and the center pin on the connection plug. The outer pins on the plug seemed to be the primary - both measured 1.2 ohms.Try reading from the plug connector to the primary coil connections.. typically ingition coils are wired with the two coils having a common ground. The center pin may not be connected to anything. I'd expect to see something around 10K on the secondary side.

[Dave_Faria]

I had tried reading from the primary winding to the secongary plug connection just in case. It still read infinity.

I did check the male plug that connects to the coil a little earlier from the center pin and it does show grounded to the frame of the bike. It looks like it may connect to a ground lug on the cylinder. Two things I'm going to try:

1. clean the ground lug on the cylinder if it is indeed the ground for the ignition coil.
2. extend the cylinder ground back to the engine body and connect it to or around the main battery ground under the ABS Modulator. I'm just looking at the any electrical insulating due to gaskets and anything that might cause a weird ground path.

If this doesn't fix it then the coils ARE just crappy as you say!!!

[deilenberger]

I had tried reading from the primary winding to the secongary plug connection just in case. It still read infinity.
Dave - this was on a new coil?
I did check the male plug that connects to the coil a little earlier from the center pin and it does show grounded to the frame of the bike. It looks like it may connect to a ground lug on the cylinder. Two things I'm going to try:

1. clean the ground lug on the cylinder if it is indeed the ground for the ignition coil.
2. extend the cylinder ground back to the engine body and connect it to or around the main battery ground under the ABS Modulator. I'm just looking at the any electrical insulating due to gaskets and anything that might cause a weird ground path.

If this doesn't fix it then the coils ARE just crappy as you say!!!
There is also a possibility that you can't measure the secondary resistance on these coils.. they may include a spark-gap ignition noise supression - like that used on K75 plug wires (which also can't be measured for resistance.) That wouldn't surprise me a bit since some sort of noise suppression is required to keep from interferring with the digital electronics.

[Dave_Faria]

Spark-gap says to me two electrodes that will wear due to the arc between them. That may explain why they fail. The gap becomes too great for the arc to cross. Am I understanding correctly as to what a spark-gap is??? We need a diagram for the coil.

[deilenberger]

Spark-gap says to me two electrodes that will wear due to the arc between them. That may explain why they fail. The gap becomes too great for the arc to cross. Am I understanding correctly as to what a spark-gap is??? We need a diagram for the coil.It's a gap - but it doesn't tend to wear out since material taken off one side is deposited on the other.. it's in a much kinder environment than inside a cylinder under combustion pressure. The wires on a K75 have been known to go well over 200K miles..

[Dave_Faria]

Not being able to determine exactly why these fail I'm going to assume there is an impedance at the coil ground at the cylinder due to corrosion. Since the primary voltage is going to be a step voltage the secondary voltage will be some sort of complex waveform. Who knows what voltages are being generated accross what componets. So my wag will be to clean the plug connector to the coil and cylinder ground and hope the coil will last. Also I've never said - my coil lasted 53k miles. I will use isopropyl alcohol at the connector and a pencil eraser at the cylinder.

[peterleo]

Low quality coils would go a long way towards explaining the failures. Right now I'm running the police type coils with extra suppression and the bike is running as good as ever if not better. I wonder if there is some aftermarket outfit that makes better coils. I'm thinking that there might be if these coils are used in both the cars and the bikes which should make for a pretty good after market.

Thanks for all the input guys....................Peter

[Dave_Faria]

My local dealer replaces the police coils more often than the regular. One thing I checked this evening was the resistance at the cylinder ground on the side that failed while the engine was cold(.5ohms) and at running temperature(6ohms). I think that is a significant increase in resistance. It is not much of a voltage drop if the current is DC but, if you have a high frequency pulse such as what might be seen with an ignition it could be significant. Again it is just my wag but, getting the ground resistance where stays at .5ohms and does not change with temperature will eliminate it as a possible problem. The good side with the good coil went from .5ohms(cold) to 1.5ohms(hot).

[peterleo]

I too have heard that dealers replace the police coils more often but I'm told thats on account of the cop bikes being left with the engine off but ignition on to power lights and radios and such.