Re: '86 560SL no ignition spark???

OK, I will take the coil into work to check the resistance from pos to neg.
My cheap meter looks like 0 ohms. It won't clearly resolve 3 ohms.

I expected some resistance from the spark out terminal to the coil body
ground / mount but it shows an open connection. Is this to be expected?

Thanks,
Joe

"Scott Gardner" <gardners14@xxxxxxx> wrote in message
news:oitui1dnl3pn70b1g65rgc5nhn3gier60o@xxxxxxxxxx
> On Mon, 19 Sep 2005 20:48:44 -0500, "jc7" <no@xxxxxxxx> wrote:
>
>>Thanks for the reply.
>>I was expecting to see continuos sparking. I will try it for a single
>>spark. The battery has a good charge. Both of the coil terminals had 12v
>>with the ignition on. I'll try the other checks tomorrow.
>>Thanks,
>>Joe
>
> Good luck - let us know. I wouldn't worry about trying for a spark
> from the coil wire - if you have the wire too far from the ground when
> you turn on the ignition, you can possibly damage the electronic
> ignition. (Not likely, but there's no reason to take the chance when
> the voltage and resistance checks will tell you everything you need to
> know about the condition of the coil.
>
> I'd still do the resistance check on the coil wire itself, though.
>
>
>
> (Continue reading only if you're interested in how an ignition coil
> works)
>
> An ignition coil is really two concentric coils wound around each
> other, but not making physical contact. The primary winding has a low
> resistance (I'll use 3 ohms as an example), and the secondary winding
> has a high resistance (I'll use 10000 ohms). The 12V battery voltage
> applied across the primary winding sets up a current of 4 amps (12V
> divided by 3 ohms) in the primary winding. Since the two windings are
> wound around one another, this causes a magnetic field that also sets
> up a 4-amp current in the secondary winding.
>
> When the distributor rotor hits one of the spark plug terminals inside
> the cap, the secondary winding now has a path to ground through the
> sparkplug. A coil resists any change in current, so it will try to
> maintain the same 4-amp current it had before it was grounded. The
> only way it can do this with its 10000-ohm resistance is to set up a
> very large voltage (in this case, 40,000 volts, which is 4 amps
> multiplied by 10000 ohms.) This is a high-enough voltage to bridge
> the gap between the spark plug electrode and the spark plug body, so
> you get a nice fat spark to ignite your air/fuel mixture.
>
> As the rotor continues past the spark plug terminal, the circuit is
> broken and the secondary winding has a few milliseconds to be "charged
> back up" by the primary winding before the distributor rotor gets to
> the next spark plug terminal and it all happens again.
>
> So, anything that increases the resistance of the primary winding, or
> decreases the resistance of the secondary winding, will decrease the
> voltage from the secondary winding, and you may not get a spark. The
> most-common problem is an open or shorted winding, which you'll detect
> when you do the resistance checks.
>
> --
> Scott Gardner
>
> "A child of five could understand this! Fetch me a child of five."
>


.

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