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01' Guzzi V11 Ignition Coils Melting (Earthing Issues?)


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So i've got a doozy

 

We have here a 2001 Moto Guzzi V11 Sport (40 000klms) running on one cylinder. It originally melted its right side ignition coil and blew a fuse.

Myself and the local mechanic thought we had diagnosed our V11 sport and so we've replaced the ignition coil, we ran the bike on both cylinders for about 5 mins at 1500rpm and FZZZZT (smoke emerges) so now we've melted another, our local mechanic has looked through the bike and believed it is now an earthing issue due to faulty wiring.

 

The Idea was that Voltage was going into the Coil, and not enough was earthing, Thus overheating the Coil.

 

He's contacted us just now and no faulty wiring can be found.

 

The only thing i can think of is that our right side ignition coil is rubber mounted fairly loosely where as the other seems rigid, however i was under the impression that the black cable is the earthing cable and the red is the positive feeding the spark?

 

Before we put the third one in we figured we'd ask the question before wasting more ignition coils here.

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Coils do come in two distinct varieties when it come to the primary resistance and I agree the problem is with too much current through the primary side. TCI (Points fall into this) or CDI. TCI coils

Is this my wife's secret account? 

To burn up the coil (twice !), there must be too much current somewhere.  On the secondary side, the resistance in the plug or the cap limits the current.  In the old days, the current in the primary

For the secondary coil. The primary one gets its ground switched through the ecu.

The ECU case ground commonly gets loose.

 

Certainly, the main ground (earth) to the gearcase behind the seatlock has gotten a lot of attention (and should!!)

Hard to get the smoke back in the wires!

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No earthing or ground issue here. The problem seems to be overheating of the coil. No ground, no current, no heat.

I'm somewhat tempted to say he should drill a hole in the back of the coils to let the surplus voltage out, to get some additional internal cooling and, probably best of all, to establish a manhole for regular spray maintenance.

 

[image]www.hk-auto.de/grafik/Emblem/zuend.gif[/image]

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ignitran.gif

 

To burn up the coil (twice !), there must be too much current somewhere.  On the secondary side, the resistance in the plug or the cap limits the current.  In the old days, the current in the primary side was limited with a "ballast resistor".  These days, that function is integrated into the ECU.  So, make sure the secondary side has the proper resistance first, then you are left with a highly unlikely failure in the ECU.

 

BTW, the drawing above has the transistor in the wrong place.  It is between the coil and ground, inside of the ECU.

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As far as I know they have skipped the resistors also inside the ECU. You don't want to have one there anyway. To save the coil from frying the on-time is restricted by the software (the MyEcu offers this parameter for fiddling even).

 

I don't think you can make anything wrong on the secondary side besides setting the resistance to big.

 

Because the bike was running with the new coil for a certain time they might have installed wrong coils before, may have tuned the software for more spectacular performance, or just want to entertain this forum. You never know. I'm curious what will come up as solution.

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Well if you want to get technical . . . In the ECU there is usually an ignition coil driver chip.  I doesn't have a simple resistor, but controls current with more intelligence looking at voltage waveforms, short detection, overheat detection etc.  The on time controls the dwell, i.e. the time it takes to get the magnetic field to maximum before you open the primary.

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Such may exist, why not. I'm no expert, so I'm a bit guessing, sure.

The MyEcu does the job based on an 8bit Atmel chip driving 2 MosFETs for 2 coils and 2 smaller ones for the injectors. That's it. The rest is IO, pressure sensor and voltage stabiliser. It works perfectly and totally satisfying.

The 15M Marelli unit, the one we're talking of, is basically the same, although some more custom chips can be found on it. It could well be that some of them do complicated things,but as long as obviously all necessary functions can be realised by obviously clever software I see not much reason why they should invest in tricky hardware. It's a cheapo for leisure articles like bikes and scooters, it's not an automotive product. And it was developed 20 years ago.

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The ECU is grounded internaly via the harness, the cable going to the housing is for the EMC shield only.

A bad ground, a fault in the harness, probably can have funky funny effects, maybe destroy it even. Switching the coils for instance is no trivial task, I suppose the chips have to handle several hundred volts and rely on a reliable path for this. Again, I'm no hardware engineer, but bad ground usually is bad for such stuff.

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What is the condition ( resistance ) of the spark plug wire , cap and the spark plug ?   Measure all three and report these numbers . To check the spark plug , you measure from the spark plug center electrode to the top of the spark plug . Remember , an open in the secondary will increase amperage in the primary . 

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Here's the schematic

 

http://www.thisoldtractor.com/guzzi007/schematics/1999_V11_sport.gif

 

A Red / Black goes to one side of both coils, this is + 12 Volts straight from the Power relay, it also feeds both injectors and the pump.

 

 A Green wire goes from one coil to the ECU connector pin 20

A Green/Black from the other coil to the ECU connector pin 14

These pins are only held to ground (chassis) for a split second each cycle

Pins 23 and 24 are connected by a black wire to battery Negative for this purpose.

 

I'm guessing you have a short on one of the wires holding the coil grounded either that or a bad ECU

 

If you unplug the ECU and turn the key On you should measure +12 on both pins and the coil shouldn't show any sign of heat because there should be no current flowing in it.

 

Looking at my drawing V11 Sport ECU Test points I see the resistance of each coil I measured at 0.7 Ohms so you can see it will get hot quickly with 17 Amps flowing continuously.

 

Using your Ohmeter measure from the 87 socket of relay 5 to 20 and 14 of the ECU socket, should see 0.7 in both cases.

 

Send me a PM with your e-mail address and I will send you the drawing.

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As a nice side effect I found this interesting site: http://mgaguru.com/mgtech/ignition/ig104.htmIt's talking about MGs, reversed polarities and more. Check it out, it offers a nice read.

I stepped over it because of the schematics, which very much better resemble the internals of the V11 coils. Just replace contact and condenser with ECU. As the 2 coils share a common ground also a shortage on the HT side could theoretically cause a continuos current and overheating of the unit. See post 2 :) Anyway, I still can't imagine how the engine would run at all with a shortage on this side, the more as this thread is fused with 15A.

 

@gstallons: what do you mean with "an open in the secondary"? Isn't it meant to be open at the spark gap?

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