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Discussion Starter #1
Hey all. I just wanted to see if anyone has tried to remove the two bricks under the tank (ignition coils), and tried to replace them with later model coil on plug units.

I don't see much of a challenge in terms of wiring / making an adapter harness, but I was curious to know if the 2007+ coil on plug units fit the older motors without too much hacking / slashing. The extra space / weight savings seems to be worth the trouble.

Any comments / ideas would be welcome.
 

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Hmmmmm.....there is only the one power wire and ground wire (to the ECU) for the paired coil..... Just have to wire the pairs in series......I am concerned that the voltage drop would be too high between ??....so wire parallel circuits power to each, ground from each to the ECU.? But then your current may be too high for the ECU ?..

Need to think on this and do some math........

Noel, what think you?
 

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Discussion Starter #3
I would assume the coil on plugs would be wired in parallel to produce the same wasted spark setup. The ecu would still deliver the same pulse, but it would split to the individual plugs. Albeit, I have not cut into the existing coils, but it appears to be two separate windings. I have seen some jap bike conversions done, so was curious if we could make it work.

The reason I am so interested, is the Marelli ecu is being ditched for a Microtec, so since we will be revising some other bike circuits, why not try to eliminate the antequated coils...
 

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The two separate windings in the coil are the primary and secondary.

Battery power goes to one primary terminal and the other terminal connects to the ECU. The ECU fires the plugs by disconnecting the lead from the primary (breaking the ground path), just like a set of points opening in an old points capacitor system.
The collapsing magnetic field created in that winding passes through the secondary windings inducing a high voltage.

The secondary winding is connected at either end to the spark plugs which present air gaps to complete the circuit to ground. The high voltage/current flows to ground by arcing across the air gaps. On one plug from the cylinder head to the center spark plug electrode, and at the other plug from the center electrode to the cylinder head. Which direction the current flows is determined by the polarity of the voltage.

As the secondary winding completes it's circuit to ground via the spark plug air gaps it creates a magnetic field that expands through the primary windings. That expanding magnetic field induces a voltage in the primary that is very low amperage but very high voltage. This is called the primary peak voltage and can be used as a measurement of the ignition system efficiency and spark generation. A modern ECU will utilize this signal to know if the ignition is functioning or not, creating Detected Trouble Codes if it doesn't see what it expects. The DTC is read using diagnostic software and may or may not generate a "check engine" or fault code on the dash.
This primary peak voltage is generally around 200 volts.

So this is my concern with the two parallel stick coils.....can the ECU handle double the expected primary peak voltage?

I am sure the coils would each fire as expected (ECU breaking the ground path as normal), but you will have two secondary windings collapsing at the same time instead of one......so how long will the internal circuits in the ECU be able to handle the increased reverse voltage spike?
 

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Discussion Starter #7
The two separate windings in the coil are the primary and secondary.

Battery power goes to one primary terminal and the other terminal connects to the ECU. The ECU fires the plugs by disconnecting the lead from the primary (breaking the ground path), just like a set of points opening in an old points capacitor system.
The collapsing magnetic field created in that winding passes through the secondary windings inducing a high voltage.

The secondary winding is connected at either end to the spark plugs which present air gaps to complete the circuit to ground. The high voltage/current flows to ground by arcing across the air gaps. On one plug from the cylinder head to the center spark plug electrode, and at the other plug from the center electrode to the cylinder head. Which direction the current flows is determined by the polarity of the voltage.

As the secondary winding completes it's circuit to ground via the spark plug air gaps it creates a magnetic field that expands through the primary windings. That expanding magnetic field induces a voltage in the primary that is very low amperage but very high voltage. This is called the primary peak voltage and can be used as a measurement of the ignition system efficiency and spark generation. A modern ECU will utilize this signal to know if the ignition is functioning or not, creating Detected Trouble Codes if it doesn't see what it expects. The DTC is read using diagnostic software and may or may not generate a "check engine" or fault code on the dash.
This primary peak voltage is generally around 200 volts.

So this is my concern with the two parallel stick coils.....can the ECU handle double the expected primary peak voltage?

I am sure the coils would each fire as expected (ECU breaking the ground path as normal), but you will have two secondary windings collapsing at the same time instead of one......so how long will the internal circuits in the ECU be able to handle the increased reverse voltage spike?

Thanks for the great detailed answer esq'z me !

I have yet to put the time into looking how ignition coils work, as I thought this might be an easy mod, vs an electrical engineering project. Given your explanation of the induced feedback voltage through the primary winding, one would assume, that if two coils are paralleled up, the feedback would be an average of two voltages generated by the coils, and the signal would present itself similarly to the standard single coil wasted spark design. The only difference being the averaging would be done in the parallel wiring of the primary coils, vs within the primary of the ignition coil. I would assume that since the varying factor in all of this is the spark / gap itself, any differences are created there, and similarly averaged at the ignition coil since this is wasted spark. Also, since the inductance / resistance of coil on plug coils would technically be considerably smaller since they are optimized for single plugs, vs two plugs on the external coil, the ECU should really not see much of a difference.

Since I am dealing with Chris at X-Bikes for the ecu, maybe he will have some feedback, otherwise it may be time to anti-up and get my hands on some coil-on-plugs, and do some testing. In my head all this should work, however I am more concerned with whether they will physically fit the engine case without much fuss.
 

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The modern small stick coils are very effecient designs. The peak voltages created are comparable to the older much less effecient larger coils utilizing spark plug wires and caps. Single coil grounded on one side or dual lead coils doesn't matter.
Fouled spark plugs present a short circuit that reduces voltage peaks and larger air gaps on plugs conversely increase peak voltages.
Have to go back and refresh my memory on the parallel circuits and voltage/current.

Anyway, certainly should work, and would in an old points ignition system....modern transistor controlled systems are more delicate.

The good old wasted spark systems are a throw back to simpler technology when multiple sets of points and coils for a 4 cylinder engine were costly and problematic. Our older MVs using that are a direct result of using a ECU designed for a 2 cylinder engine.....we also have a wasted fuel spray from the injectors. Makes fuel tuning a bit wonky!! The old carbureted engines didn't have that problem.

So....since you are getting a more modern ECU....why not redo the wire harness for the injectors, get stick coils, and get rid of the wasted spark and spray both?

You could use just about any 12v stick coil on the market. Should be no problem fitting into the head of your MV.
 

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Discussion Starter #9
Good god. I totally forgot about the wasted spray.... I will have to talk to Chris at X-bikes on that one. The electrical part of eliminating the wasted spray is easy enough by adding a few wires to the bikes harness to interface with the dedicated injector outputs on the new ECU, but the lack / absence of the cam signal to know which cylinder is firing may be an issue. By no means am I am engine guru....
 

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Cam Position Sensor could be emulated by a manifold air pressure sensor. Plumbed into the throttle synch manifold spigot and hose on the #1 cylinder, the ECU could pick up the pulse when intake valve opens and thereby interpret cam position.
A lot of twin cylinder bikes use a MAP sensor for that purpose.
 

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Discussion Starter #11
Ed, good idea. I will have to see what can be done on the Microtec after we get everything running. Chris is fitting one of the new Microtec M232 Ecu's which has far more capability than the previous conversions he has done. Should be interesting to say the least. I will document / post as we make progress.

Anyhow, I did do some reading up on the whole coil on plug conversion process done by others in the 2 wheel world, and you are pretty much spot on with the series connection idea.

The coil on plugs are totally different in terms of impedance compared to the stock monster coil, so the ECU actually does not much, if any load change as long as the right coils are used. I am thinking stock MV coils which are three wire units, but there are even newer tech 4-wire versions, which present almost no load to the ECU. They have built in drivers / transistors in the coil on plug assembly, which only need a small signal from the ECU to fire. Very cool.

So anyhow, this looks like it will be on the "to do" list. Just a matter of getting the right parts, and building an adapter loom.

Thanks for everyone's input. I will post the results as they happen...
 
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