Re: Coil on backwards, did I fry my module ???
The original Ford DuraSpark started being used about late '74,
then almost totally used in '75.
It was just an electronic ignition like most everyone else's
at that time. The spark wasn't really much hotter, but it
did get better control over dwell variations due to loose
distributor bushings - a big help in controlling emissions.
GM HEI started at the same time, '75. The GM was a hotter
spark, more voltage, more current, and a longer spark duration.
Their "secret" wasn't really a secret, they no longer used an
ignition resistor, used an E coil, and their output transistors
About '77 or 78 Ford got around the GM patents and came out
with their DuraSpark II. Then they had something just as
good as GM's. Both ignition systems finally had the same
power, voltage, current and duration. This was really needed
since the mixtures were getting leaner every year, it was
much harder to light a good fire in the chamber.
Both used the larger cap because the extra distance between
terminals was needed for dielectric strength - insulation.
The DuraSpark II uses a different module connector, more
square than the DuraSpark I -- similar, but different.
(OK, it wasn't called I until there was a II.)
Whenever you see the larger Ford cap (stock, not conversions)
you'll find the module is the more powerful DuraSpark II.
The wiring is slightly different on those, and they have
another wire to contend with.
The TFI (Thick Film Ignition) came even later - that's the
one with the small flat module mounted directly on the
distributor. The reason they did that was to try to get
around the false triggering problems the Dura I & II
experienced. The Dura's were very sensitive and would
trigger from electrical noises. (GM got around that problem
by having a higher voltage signal from the pickup coil - 8 tips
passing each other to trigger vs 1, so they could use a
less sensitive module.)
The Ford TFI used the E coil.
The resistance on the E coil's primary is roughly 1/2 that
of the round coil used originally on the DuraSpark I.
The round DuraSpark II round coils were somewhere in between.
The DuraSpark II module also has a built-in current limiter
in it - that's why it does not overheat when the key is left on.
DuraSpark I - when you turned the key on current rushed into
the coil and continued flowing at full strength, ready to fire,
but if you didn't start it it continued pushing the current
through the coil. The original coil resistance was high
enough that it didn't harm the module - usually.
But when you use a coil with less primary resistance, the
current is greater, the output transistors have to dissipate
more heat, often too much -- "Pop."
The DuraSpark II has the current limiter - when you initially
turn the key on, current rushes into the coil to charge it
up, but then the limiter lowers the current substantially,
saving the output transistors.
That's actually a side benefit of the current limiter, it's
main purpose is to limit the amount of magnetic field to
the optimum level in the coil. There is something called
over-saturation in a coil, decreasing it's output - you
can pack it too tight with magnetic field.
I've always been under the impression that the Ford
DuraSpark II did NOT use an ignition resistor in series
with the coil, just straight 12 Volts to it. The GM does
not use the resistor.
But - I was looking at a schematic to be able to tell you
the slight difference in wiring between the I and II and my
book shows a resistor. It may be a misprint, need to
Not being a Ford enthusiast I've always tried to avoid them
- starting with when they came out with their electronic
ignition in '75, then for sure I lost all respect for them
when they went to computers.
Now - using an E coil with a DuraSpark I -- with the original
ignition resistor still in place, will provide a slightly
hotter spark than with the original points ignition or the
Dura I's coil, but not what it could if it was done right.
But - you have that overheating potential.
Best way then, more reliable, is use the round coil designed
to be used with that mudule.
Best way - do the complete conversion, later II module and
all - and if the ignition resistor is different or none,
do it too.
Then you'll have a spark rivaling an HEI.
I'll try to find out about that resistor and let you know.