Dyna Ignition Problem

[Karl Von]

Hi All, I know this does not pertain to the V11's but I am trying to help a friend debug a Milie GT with a Dyna ignition. The problem started with the bike losing spark on the left side. We swapped the left plug wire to the right coil and got spark. We thought maybe a bad coil. Later we lost spark on both sides. We are getting 12v to the + side on each coil with the ignition on, but we are also getting 12 on the - side of the coils.

 

For comparison I checked the voltage on my Cal 2 with the Dyna. I have 12V on the + side and around 2v on the - side with the ignition on.

 

I next took the white and black wire from the black box and grounded it to the frame, which should cause the plug to spark but got nothing on either side.

 

 

Anyone have any ideas ? Maybe the black box is shot. When checking the coils with a Ohm meter do you just read across the + and - ?

[Guzzi2Go]

If both bikes use same ignition coil type you should not be getting different results when using a voltmeter.

 

Check the coil resistance with ohmmeter (ignition off, across the +/- terminals). If the result is not zero or close to it (compare with coil resistance on your bike), measure resistance between the coil's negative terminal and the frame (negative terminal on the battery).

 

From measurement on your bike you get 10V tension drop on the coil, 2V on the connection to ground.

 

Usually resistance to ground is a single digit ohm value (less than 1 is considered a good one). A bit puzzling that you read 2V on it, as it indicates that there are 2A of current @1ohm running through your coils. If that is how it is designed(), that would mean your coil should measure ~5 ohm and it will be difficult to determine if your friend's coils are busted (short circuited) using ohmmeter. As I can recall there is a whole science out there on how to measure small resistances.

 

Anyway, if you can read 12V on the negative terminal, check the coil-frame connection. Should have really low resistance, practically nothing. If not, clean up the contact area.

 

If you measured more than 5 ohm on your "healthy coil" (more like 50 or even 500), I'd suggest you clean the contact areas on both of your bikes.

 

[Karl Von]

One thing I forgot to add was my Cali is running the stock coils and the Millie is runing the Dyna's, but both bikes have the Dyna 3 system. the orginal owner of the Millie mounted the Dyna coils with a clamp around the plastic body, which is a issue as the metal mount tabs on the Dyna's also act as a heat sink, which from what I have read, they need.

 

I am going to measure the resistance on the coils, and measure the voltage on the 2 wires from the black box to the - side of the coils. I am leaning towards the box failing

[Guzzi2Go]

Ok, I educated myself a bit about Dyna coils and they do have resistance in the range of 0.5 to 5 ohms.

 

http://www.dynojet.co.uk/dynatek/ignition.htm

 

There are two ways of interpreting your measurument results:

 

1. The coil is shorted - hence 0V drop on the coil itself, 12V drop on the "ground" resistance. Should draw fair amount of current (>10A), and things are getting hot. Dangerous!

 

2. The coil is OK, the grounding is not. Too high resistance, which is limiting the current (hence energy) through the coil. Measure resistance to the ground (negative battery terminal). Try to scratch to the bare metal to get the values as low as they go.

 

However, you are probably right. Lack of trigger impulse either from the box itself, or from the ignition distributor is probably causing the problem.

[jrt]

Remove the leads from the dyna coils and measure the resistance. Then compare that to the resistance of a stock coil. You might need to add a resistor to the dyna coil. I cannot remember what the Guzzi coil resistance should be...5K maybe? You better check.