Ignition Coil Question

[imported_TheMan]

Alright, one of the strangest things I've ever seen and I'm leaning towards it being abnormal..

I couldn't get the engine to start and figured I flooded the engine, so I pulled the plugs to dry them out and turn the engine over a few times to expel what gas I could. (The engine did start after I put the plugs back in, but thats not the point)

I disconnected the coil to distributor wire while I was turning the engine over.
While doing this, a high energy spark would travel from the coil plug to either the positive or negative terminals of the coil fairly regularly.. I've never seen anything like this before and am wondering what, if anything, it might mean. It seems that without the distributor connected to trip the coil, it should not emit a spark, but I am not sure if there is any variation from my other experiences due to the thunderbolt ignition system. I'm also not sure why the spark jumps to either the positive or negative side instead of just the negative side..

It is a '90 Mercruiser 4.3L with Thunderbolt ignition. Anyone ever see anything like this before or have some input?

Thanks in advance.. I might take a video of it just because it is kind of impressive..

 

[Don S]

Re: Ignition Coil Question

You should be grounding that coil wire when you pull it out of the distributor cap. That arching with no place to go can damage some electronic ignition systems.

 

[MikDee]

Re: Ignition Coil Question

Wait, you're never supposed to turn the motor over without grounding the coil wire! I've had this happen it is arcing (carbon tracking) across the coil terminals because the built up spark has no place to go. This can damage the tower of the coil, and leave a permanent path for the spark to short circuit. Make sure you clean off any carbon tracks, maybe with some alcohol, or acetone. Then for any future diagnostic cranking, either ground the main coil wire, Or, tempoarily remove the small wires going into the coil (so the there's no power going thru it).

 

[imported_TheMan]

Re: Ignition Coil Question

Thanks for setting me straight.. Guess I was falsely presuming the charge would hold..

Lot easier (and more fun) to assume the previous boat owner was an idiot rather than the current one

 

[wire2]

Re: Ignition Coil Question

Normally, the combined gap of the rotor and spark plug decide what the output voltage of the coil is. It's a simple case .0xx" gap allows yy kilovolts.

With the coil to rotor wire off, the voltage builds much higher, to the extent that it will jump to either + or - terminal. It sees almost no difference between the 2 posts, (12 volts compared to ~15,000).
It's predictable and normal, given the circuit.

 

[HT32BSX115]

Re: Ignition Coil Question

Uh.....what ever you do, keep a fire extinguisher handy. Exposed sparks have a nasty habit of igniting combustible vapors!

Cheers,



Rick

 

[bruceb58]

Re: Ignition Coil Question

Normally, the combined gap of the rotor and spark plug decide what the output voltage of the coil is. It's a simple case .0xx" gap allows yy kilovolts.

With the coil to rotor wire off, the voltage builds much higher, to the extent that it will jump to either + or - terminal. It sees almost no difference between the 2 posts, (12 volts compared to ~15,000).
It's predictable and normal, given the circuit.

Agreed....and since the voltage is going to be a lot higher than it normally would, you are severely affecting the life of your coil by doing this. This is why running with too wide a gap or lossy spark plug wires will also damage your coil.

 

[Haut Medoc]

Re: Ignition Coil Question

Uh.....what ever you do, keep a fire extinguisher handy. Exposed sparks have a nasty habit of igniting combustible vapors!

Cheers,



Rick

Yup!.....
Get a jumper wire, shove it in the coil lead & to the block=20 seconds....

 

[ron7000]

Re: Ignition Coil Question

i learned in school the number of windings in the coil, # in the secondary high voltage side to the # in the primary 12v side, is what determines output voltage. those "marine" coils must work differently

 

[Don S]

Re: Ignition Coil Question

Nope, they work the same as automotive coils.

 

[Bondo]

Re: Ignition Coil Question

Ayuh,......

What you learned in school is the Voltage Available.........

How Far it has to Jump, determines how much Voltage is Used........

 

[wire2]

Re: Ignition Coil Question

i learned in school the number of windings in the coil, # in the secondary high voltage side to the # in the primary 12v side, is what determines output voltage. those "marine" coils must work differently

That applies only if you have a sinusoidal (sine) wave going to the primary.

In this case, the field is built up relatively slowly with the points closed, (or electronics on). Then when the points open, the field collapses very fast, you get primary to secondary turns ratio volts but also mutual induction between the secondary turns. That can greatly increase the output voltage if it's not limited by a specific air gap to ground.

 

[wncrjb]

Re: Ignition Coil Question

I always just remove the wire from the positive side of the coil..........

 

[ron7000]

Re: Ignition Coil Question

That applies only if you have a sinusoidal (sine) wave going to the primary.

In this case, the field is built up relatively slowly with the points closed, (or electronics on). Then when the points open, the field collapses very fast, you get primary to secondary turns ratio volts but also mutual induction between the secondary turns. That can greatly increase the output voltage if it's not limited by a specific air gap to ground.

are you saying that if you decrease the spark plug gap the coil will output more voltage on the spark plug side? if not, then please explain.

what do you mean by mutual, when you say mutual induction between the secondary turns?

 

[bruceb58]

Re: Ignition Coil Question

are you saying that if you decrease the spark plug gap the coil will output more voltage on the spark plug side?

It is the opposite.

The smaller the gap...the lower the voltage.

 

[ron7000]

Re: Ignition Coil Question

is all that is trying to be said:
the smaller the spark plug gap, the less voltage required to make a spark jump that gap ?

I did not interpret that meaning from

Normally, the combined gap of the rotor and spark plug decide what the output voltage of the coil is. It's a simple case .0xx" gap allows yy kilovolts.

nor from other statements made about voltage available, voltage used, and "That can greatly increase the output voltage if it's not limited by a specific air gap to ground".

what is a lossy spark plug wire?

 

[bruceb58]

Re: Ignition Coil Question

what is a lossy spark plug wire?

Basically...hi resistance so that the instead of the energy being transmitted to the gap of the spark plug, there will be an alternate path found to ground somewhere.