Wasted Spark Ignition systems 1

[Spud72]

I wonder if anyone can help/confirm the following for me.

I'm quite happy with how the above system works when all's well, ie complete circuit. But, the question I need answering is this... When we go open circuit on 1 plug/lead I say that the other plug will fire and will fire the same (ie Negative or Positive) polarity spark as it was previously?

I've reached the conclusion that in order for this to be true the circuit must be completed somehow, either by finding its way back into the coil via any means possible (through the vehicle body to the Ignition terminal side of the Low Tension circuit and then "Track" through the magnetic field in the coil back to negative)? Does this sound feasible?

When I 'scoped this using a DSO I found that the spark remains neg or pos charged (as previous) and appears to contain some of the voltage (opposite polarity) of the U/S plug? True?

I also 'scoped what appeard to be pressure fluctuations in the coil! I'm assuming that's what I was seeing as the pressure couldn't be dissipated through the other plug/lead as it was open circuit?

Any help would be much appreciated. Thanks

 

[Ron07663]

Not a good idea to open circuit this type of coil. When it fires the no load voltage will rise in excess of 40kV until some dielectric breaks down external or internal to the coil. This is very stressful on the coil and will shorten its life.

 

[Spud72]

Excellent thanx.

I thought that this might be the case. Do you know if it also damages the Low Tension side, especially with reference to the Transistor and capacitor?

 

[Ron07663]

I have seen coils fail by internally shorting from secondary to primary. When this happens on wasted spark systems often you will see only one of the secondary outputs fire. The ignition modules can be affected but they are protected from high flyback voltage and are current limited so they take a lot of abuse.

Ron

 

[thrashercharged]

Spud72 - yes, you're correct that the circuit has to be completed (current has to flow from one coil terminal to the other). So if you go open circuit on one terminal, the other plug will fire only if current gets to it somehow by any means possible. It'll still fire in the same polarity.