Re: Would a bad ballast resistor cause an 86 F250 not to start?

In article
<y63tf.205056$qk4.35450@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"Stephen H" <hansensw@xxxxxxxxxxx> wrote:

> the engine wasn't that old, perhaps 7 years F.I.

Not so much a question of age or fuel system, it's a question of
what exercises that particular simulator was designed to emulate.

> Modern cars still do reduce voltage to the coils, mostly in the ignition
> modal if I remember correctly.

They most certainly do not.
Don't take my word for it, pop some hoods and do some testing
with your voltmeter.
Better yet, use a lab scope, that way you can see all the
dynamics over time.

> The critical point being that during a start, the car pulls the available
> battery voltage down to 9-10 volts, and a full 12v coil wouldn't have enough
> voltage at that time to saturate and fire correctly.

Problem is, coil saturation is not a function of voltage, it is a
function of current.

> It applied it the old days and still today.
> Every starter test we do shows 9-10 volts at start and the car passes with
> that number.

Yes, and modern e-core style coils will output enough secondary
when fed 9-10 volts to start an engine, especially now that we
have advanced fuel control and delivery.

Going back to the original post; the Ford Duraspark system in
question will actually shut itself off when cranking voltage goes
under 10 volts. You can demonstrate this for yourself by
connecting your carbon pile to the battery terminals, installing
a spark tester on the coil wire, cranking the engine (remotely)
and adjusting the carbon pile during crank. At almost exactly 10
volts, the spark will go out.
.

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