Coil Over Plug mod (COP) for standard coil removal

For those wondering all my hoopla about parallel vs serial, this is exactly why.

Each coil driver circuit can only output a certain number of amps per channel (per coil) and a total for the whole circuit combined. Exceeding either will result in MOSFETs entering protection mode, or overheating, depending on the specific IC used.

By using the 2002-2003 R1 coils, the circuits are already drawing roughly double the amperage compared to the stock coils.

When using the ones Joe had at 0.7 ohms, the amperage is roughly quadrupled at the ECU side, and is almost certain to end up tripping any built in protection circuitry (if any) with per channel amperage exceeding 20 amps (way too much for a price point ECU).

Since doing this mod, I've learned there are a massive number of compatible coils, some are safer to use than others. The R1, 2002/3 coils are a good fit electrically, but beware any coil advertised to fit an R6 or Vmax, as Joe found out the hard way unfortunately they won't work.

I don't go under my tank much, and the stock coils are not in the way of changing spark plugs, that I recall, so stock is fine for me.

Yes, the power is inversely proportional to the square of the resistance - so when you half the resistance as @Claviger states you double the current but quadruple the power*. (power varies as the square of resistance) (1/2)^2 = 1/4 (inverse so x 4)
But for current it is linear - you half the resistance, you double the current

But again, re series vs parallel - you can't run in series because then you only get half the voltage on the primary of each coil - half voltage on primary also means half voltage on the HT side. Don't think you want that at all. Reduced voltage equals reduced intensity spark - and maybe even insufficient to jump the std gap.
@Joesmoe asked about using a resistor in series with each coil - that is actually what I have on my 51 Chevy using the original 6V coil in system since converted to 12V - but in my case the very object in using the resistor is to get back to 6V across the coil on a 12V supply system; when you put resistor in series with the stick coils, you do the same thing as connecting them in parallel, reduce the voltage to the actual coil, with volts dropped across the resistor.

Joesmoe said:

Update: The resistance of the coil sticks MATTERS !

I purchased new items from eBay that claimed cover multiple years - this data may change -- we know 2002 spec items work -- we know shortly thereafter they don't work -- and we have heard not yet confirmed, later years still are back to compatible.

The items I purchased I blindly installed in the back, and no run.

Testing the sticks they showed 0.7 Ohm resistance, meaning they draw too much current, and the bike was shutting down.

The sticks that work need to read double that, or 1.4 Ohm (I measured the OEM coils at 2.9 Ohm). Of course, there are six sticks, and three OEM coils, so things going on here I don't understand.

I just know 0.7 doesn't cut it, and I've noticed nowhere on eBay do the sellers offer that information -- they just say "came off a running bike" or similar, which is not much to go on.

Big shoutout to @DEcosse and @Claviger for help this neophyte through this process.

More to follow.

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Thanks for the report. Now can you tell me why you are going thru this on your bike?

DEcosse said:

Yes, the power is inversely proportional to the square of the resistance - so when you half the resistance as @Claviger states you double the current but quadruple the power*. (power varies as the square of resistance) (1/2)^2 = 1/4 (inverse so x 4)
But for current it is linear - you half the resistance, you double the current

But again, re series vs parallel - you can't run in series because then you only get half the voltage on the primary of each coil - half voltage on primary also means half voltage on the HT side. Don't think you want that at all. Reduced voltage equals reduced intensity spark - and maybe even insufficient to jump the std gap.
@Joesmoe asked about using a resistor in series with each coil - that is actually what I have on my 51 Chevy using the original 6V coil in system since converted to 12V - but in my case the very object in using the resistor is to get back to 6V across the coil on a 12V supply system; when you put resistor in series with the stick coils, you do the same thing as connecting them in parallel, reduce the voltage to the actual coil, with volts dropped across the resistor.

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Exactly why I just ended simply wiring in parallel as Neville said to do, because the other way wouldn't have worked I don't think.

In Joe's case he's running a resistance of about .35 ohms per cylinder vs 2.9 ohms. We know a resistance of 0.7 ohms per cylinder works, I misspoke, the .35 is actually about 8x the current draw of the stock system, where the 0.7 load like mine and other working installs is 4x.

Bottom line - Coils below 1.4 Ohm primary resistance wired in parallel are not appropriate for this for anyone doing this down the line.

Just for confirmation, at @DEcosse ' behest, I just ran the bike with one spark plug per cylinder. I let it run for about ten minutes -- nominal.

I submit this confirms the problem before is in fact the unacceptably low (for this application) coil resistance.

Replacements ordered.

And @warp9.9 - I am far less comfortable than you at raising the tank and messing around under there, and yet I am compelled to do so.

The COP mod is being made for the very same reason you recommended removing the support bracket for the Number One coil. I thank you for that.

And playing with the bike, and overcoming the challenges, is just plain fun, and unlike my firearms, there aren't as many stupid people out there trying to prevent me from doing it.

I love the opportunity to associate with all the smart, fascinating, capable souls who frequent these pages. Thank you !

Just going to post this so people understand, DeCosse is a massive electrical circuit genious, I'm just a dude who's been pushing electronics way beyond design specs in computers for about 20 years, and competitive car audio for a bit longer.

He knows the right answer, I know the answer learned from breaking expensive parts lol. In all things electrical I definitely defer to his knowledge.

All of us are better than any one of us.

Joesmoe said:

Just for confirmation, at @DEcosse ' behest, I just ran the bike with one spark plug per cylinder. I let it run for about ten minutes -- nominal.

I submit this confirms the problem before is in fact the unacceptably low (for this application) coil resistance.

Replacements ordered.

And @warp9.9 - I am far less comfortable than you at raising the tank and messing around under there, and yet I am compelled to do so.

The COP mod is being made for the very same reason you recommended removing the support bracket for the Number One coil. I thank you for that.

And playing with the bike, and overcoming the challenges, is just plain fun, and unlike my firearms, there aren't as many stupid people out there trying to prevent me from doing it.

I love the opportunity to associate with all the smart, fascinating, capable souls who frequent these pages. Thank you !

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That's fantastic, confirms the ECU does, in fact, have some level of self protection built into the ignition circuit, or at least, the excess heat dissipation capacity to not immediately kill itself when running too low primary resistance coils.

Thanks Joe, you taught me something ew about the R3 today

Now about that ignition break up I was seeing above 7500 RPM with the bike heat soaked, I have a very strong suspicion it's exactly what you inadvertently discovered with this.

Joesmoe said:

Just for confirmation, at @DEcosse ' behest, I just ran the bike with one spark plug per cylinder....

Click to expand...

Claviger said:

That's fantastic, confirms the ECU does, in fact, have some level of self protection built into the ignition circuit, or at least, the excess heat dissipation capacity to not immediately kill itself when running too low primary resistance coils.

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It's probably simply running into a current limit situation.
When discussing this off-line with @Joesmoe I was initially surprised it was not posting any ignition error codes - this somewhat point to fact that it is not truly an ECU dictated protection per se, just running into the limits of the current it is actually able to supply (the ECU will recognize an over or under voltage situation at the output i.e. from either on open circuit (no load present) or short circuit (absolutely zero ohms to ground) but apparently does not recognize 'over'-current, just self-limits.
So I suggested the single coil test recognizing that it should still at least run with a single plug per cylinder and it actually worked, proving it was certainly load dependent and not something else inadvertent/unrelated that was causing his non-running issue.
Now the absolute numbers of the coils (that @Joesmoe had) resistance are not necessarily completely accurate, but again offline, after changing his meter battery and subtracting the offset resistance measured between the leads (0.2 ohms) he found a net resistance per coil of only 3 ohms, with the OEMs at 1.7 (which somewhat tracks the number for OEMs reported by others);
So that tells us the ECU is capable of running a load of only 0.3 ohms (!!!!) - at idle at least - without current limiting (as least outwardly as far as bike running appeared) but clearly could not sustain a load of only 0.15 ohms!
Now I certainly would not want to be running anywhere close to that 0.3 ohms load (even though it appears to 'work') but 2 x 1.4 for the 2002/3 R1 coils (= 0.7 ohms net for parallel pair) is probably 'OK'. If someone can find something with a higher impedance it would be nice though.

I'd be really curious to see what difference (if any!!!!!) there is on the dyno when only one coil is utilized - maybe something for you to play with @Claviger since you have COPS and possibly some dyno access.
Or has anyone else actually tried this to see if there really IS any power advantage in twin sparks vs single? That would be REALLY interesting.

Claviger said:

... Now about that ignition break up I was seeing above 7500 RPM with the bike heat soaked, I have a very strong suspicion it's exactly what you inadvertently discovered with this.

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So I'm actually not sure if you're meaning why you get ignition problems above 7500 due to same (current limiting) issue:
You wouldn't expect this to be the case due to frequency alone - the current does not change just because the rpm is higher, the load is still identical, although it does have to switch that load at a higher frequency, the current per cycle should be no different - although however there is the factor that the drive transistors could be suffering some thermal conductance limitation, as they will certainly run hotter as the frequency increases (because there is less 'relief' time before the next cycle, so heat will accumulate more - so could be that ...)
Here is a typical Power MosFET graph that show effect of conductance/current limitation due to temperature



The question is whether the ECU Ignition Drive transistors are really getting hot enough to limit the current - they are likely to be extremely low resistance devices, and it would take a LOT to get them to that stage where they are affected (for example, different devices of course, but my keyless ignition system utilizes devices good for about 40A each and even when pulling about 15A through them, are barely discernible as being even warm.)

It could also be simply that one (or more) of the coils is breaking down at higher temperature/frequency. It is fairly typical signature of a bad coil that they will be more likely to break down when hot and at higher rpm.