C25-coil fault but the coil isn't the problem? Pointy

[MorphingRoyals]

Hi guys,
just touching the ton (off road of course) the other morning on a brisk ride, I got a bit concerned as the bike suddenly lost power and started sounding lump......
Pulled into a layby with the warning light on and the bike trying to run on one cylinder, did a quick check over then took a slow plod home in 'restricted 325cc single' mode.....

As I had previously had intermittent firing problems on the rear cylinder and changed the coil with a cheap replacement before finding the plug to be faulty, thought maybe the 'cheap' coil could have given up and with finding a C25 fault code, went back to the original coil (only had 1500 miles on it) confident it would sort it.

Disconnected the battery to clear the memory, fired it up and was still on one with the FI showing on the dash.
Got the C25 code on again so I'm guessing the FI system is still thinking there is a problem and cutting the cylinder.

My issue is, the coil is testing fine, so is the cap, so is the plug but when I remove the power supply to the coil, the bike runs on one cylinder (expected) but there is no FI warning and no power coming to the terminals that supply the coil (tested on the 10 volt scale).

I'd at least expect the FI warning to show without the coil connected but because it isn't, I also expect power to be coming into the coil (would understand no power with 'FI' as it will cut that cylinder).

Any ideas what the 'fault' could be?

Maybe a way to clear the memory (if diconnecting the battery doesn't do it) or bypass the fault protection system to make sure it isn't causing more of a problem by finding/remembering/making up a fault that isn't there?

Thanks in advance;)

[Bibio]

the ECU is not clever enough to have a limp mode.

is there anything else that you have done to the bike recently (mods, levers etc.etc) apart from the coil issue and possibly before?

might also help if you tell us what year and how many miles the bike has done.

[MorphingRoyals]

the ECU is not clever enough to have a limp mode.

is there anything else that you have done to the bike recently (mods, levers etc.etc) apart from the coil issue and possibly before?

might also help if you tell us what year and how many miles the bike has done.

Hi buddy,
Haynes states:
'C25 - Rear Cylinder Ignition Coil - engine will run on other cylinder, ignition signal to cylinder 2 cut'

Nothing else done this year (or the last couple) other than putting the original plugs back in after a suspect iridium one seemed to be breaking down.

Bikes been fine for 40 miles since then (4 mile round trip to work a few times over a couple of weeks), not missed a beat but now firmly running on the front cylinder only.

2006 SK6, 1570 miles when it stopped running on two.

[Bibio]

sounds like another duff plug. get yerself a nice new set of plugs and stick those in. remember to take the nipple off the top of the plugs (if they have them) so just the threads are showing and push the plug cap down firmly with the little triangle on the rubber part pointing to the exhaust e.g. the rear one points towards the back and the front one points toward the front. another thing is if you pull on the HT wire instead of the cap it can snap the HT lead inside the cap.

[Red ones]

7 years, less than 1600 miles?

[MorphingRoyals]

sounds like another duff plug. get yerself a nice new set of plugs and stick those in. remember to take the nipple off the top of the plugs (if they have them) so just the threads are showing and push the plug cap down firmly with the little triangle on the rubber part pointing to the exhaust e.g. the rear one points towards the back and the front one points toward the front. another thing is if you pull on the HT wire instead of the cap it can snap the HT lead inside the cap.

Tested the plug, cap and coil to check for an open circuit as they seemed the most obvious and easily changed.

I suppose the most obvious test would be a complete plug and coil swap from front to back, that should make it a C24 (front coil) fault if it's either of those.......

I'm looking at the fault possibly being further up the line as there is no power coming into the rear coil with the positive and negatives on the voltmeter and the bike running (on the front cylinder).

[MorphingRoyals]

7 years, less than 1600 miles?

Yep, owned since new, got 900 mile in by the end of 2007 for it's first service and spent every year since promising to use it more but never getting it out more than 4 times a year.

Hoping a late start to this year would change that but not if it isn't going to keep running on two cylinders :(

[Bibio]

how many services has it had?

i would start with a new set of plugs m8. i very much doubt that its the coils.

if the bike has been sitting about check the connectors that are open to the elements then the ones that are not.

how fresh is the battery?

[MorphingRoyals]

how many services has it had?

i would start with a new set of plugs m8. i very much doubt that its the coils.

if the bike has been sitting about check the connectors that are open to the elements then the ones that are not.

how fresh is the battery?

No service since the '1000 mile' service, the George White's I bought it from went tit's up a couple of years ago and although everything has aged whilst stored in the shed, never saw the point in servicing it if it hasn't gone anywhere.
My brother is an MOT tester and the old man has been on bike since long before I was born hence having a bit of mechanical knowledge.....

Haynes says 'faulty power supply for the ignition system' as a possible cause for C25 so digging under the airbox and disconnecting/applying vasoline/reconnecting all the connectors whilst under there is on the to-do list whilst swapping the plugs and coils to see if the fault changes cylinders...

Suppose putting the 'good' iridium plug into the rear cylinder and seeing if that cures it is an easy option and would answer the possible plugs thoughts....

Battery is good, been cycling on the Optimate and never spun slow although I must admit I've noticed the headlight are almost completely out when firing it into life (sparks into life just like the first day I bought it, just now it's on one cylinder)....

Thanks Bibio!

[Red ones]

I think the lights are supposed to go out on start up. Always have on my K5

[MorphingRoyals]

I think the lights are supposed to go out on start up. Always have on my K5

Glad to hear that one, ever since my first days on an '89 TZR125 nearly 20 odd years ago, I've sworn by riding with the lights on but never agreed with recent bikes not having the option to turn them off, especially on starting.

Thanks for that :thumleft:

[Bibio]

the ECU will throw a code for any part of the chain it finds a fault with in your case it's giving a C25, this may or may not be the coil and can be any part of the chain from the ECU to the plug on that circuit.

swap the good plug from the front into the rear and visa-versa then see what happens.

don't change coils or do anything else till you know for definite that it's not the plugs. once the plugs are ruled out than trace the line back till you find the fault.

[Red ones]

swap the good plug from the front into the rear and visa-versa then see what happens.

And be prepared to take the skin off your knuckles! Serious tip- take the rear plug out first, it saves an extra trip to the front plug and having to inflict more pain on your hands. You may gather I'm not a fan of changing the front plug!

TBH you would need some seriously duff plugs at that mileage. Despite what the manual says you should be able to get 30,000 miles out of a set of plugs. But it is worth checking. I'd also check for loose connections on that circuit. It really shouldn't be major at that mileage unless.... Do you keep the bike in a garage? Does the garage have any sign of mouse activity?

[Sid Squid]

There will not be a fault code if the plug is duffed obviously, but clearly it would be worthwhile to rule them out - particularly if one of them is very old or perhaps the age of the bike.
From what you've written the problem lies in the coil circuit, be that ECU, wiring, connectors, coil.
When the bike is in a run state you should get voltage on the hot side of the LT, (as you likely know the coil negative is switched to give sparks), check the voltage there but make sure the system is lived, in many permutations of the start/run inhibitors the system is effectively switched off, so make sure there's voltage at the hot LT on other coil when testing.
As you suggest, it would make sense to swap the coils over so the known good coil is in the suspect part of the system - that would be my first move, then check the wiring from the coil back to the ECU.

An aside:

The SV has a number of 'limp modes', for instance if the barometric sensor, either temperature sensor, gear position sensor, throttle position sensor or the secondary throttle servo fails the system will default to a preset value and run with that. On the SV1000 there are some failures the system can deal with while the engine is running, but it will not restart if switched off.

[yorkie_chris]

I've seen more coil faults that are faulty coils WITHOUT giving a coil fault code including completely open-circuit coils.

Don't think the ECU coil-fault-sensing-jobby is very clever.


Broken wire/shorted connector/rusty connector/ECU fault...

[MorphingRoyals]

Thanks for all the info guys....

So far yesterday....
Changed the spark plug, still on one....
Changed the coil, still on one....
Checked power to the coil, 12 volts.....
Checked the ECM to coil wire, no break....

Nothing else is in the circuit according to Haynes so the only thing I'm left with is a faulty ECM....

Only problem with that is, with the positive and negative removed from the rear coil, I get one cylinder running (obviously) but no FI warning.
With the wiring all hooked up and the bike fired into life, starts on one cylinder and the FI warning is immediately up (C25).

I'm either looking at the ECM not being faulty as I personally would expect the FI warning C25 without the coil connected (blanket C25 faulting on that mircocircuit regardless of what is or isn't connected, not having a coil connected is a pretty big fault in my eyes!)...
Or there is a fault with the ECM, it just doesn't have the complete circuit to give the FI warning without the coil connected (ie, needing all the components connected to validate giving the warning in the first place)...

Anyone have an idea of which is more likely?

Easy answer would be to plug my suspect ECM into a donor bike and see if it runs on one but don't know of anyone with a local SV650 or trusting enough to do that with (maybe I'll go to a local bike shop with an SV650 for sale and take it for a test ride then try my ECM on it around the corner;))

[Dicky Ticker]

Better still take it back with a faulty ECM------;)

[MorphingRoyals]

Better still take it back with a faulty ECM------;)

lol, nice :thumbsup:

Suppose one question I could ask the community to help with....

Anyone out there with a working bike willing to disconnect the positive and negative on the end of the rear coil on their K2/3/4/5/6 (right side frame between the coil and regulator) and tell me if it runs on one cylinder with no FI fault or one cylinder with FI coming up?

At least I'll then know if the disconnected coil should create the FI warning or not (as it currently isn't).

[yorkie_chris]

I had one the other week which was running on one pot, infinite resistance on coil primary. No fault code. Cured with new coil.

[MorphingRoyals]

I had one the other week which was running on one pot, infinite resistance on coil primary. No fault code. Cured with new coil.

Yeah, I'd be happy with that sort of result but still getting a fault code (and thus the ECM blocking the ignition of the coil, even if it isn't physically faulty) after having changed the coil and plug plus testing through the wiring really sucks!

Beginning to think it could only be the ECM at fault.