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Duraspark conversion.

Bronco648

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So, is that what we're looking for, one Ohm of resistance? That doesn't seem like much.
 


Uncle Gump

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Resistor wire is measured in ohms per foot.

@19Walt93 knows the internal resistance for a duraspark coil. Seems to me everyone i checked over the years was right around 6 ohms.
 

Bronco648

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Here's a new question: can anyone give me an idea of what the fifth fastener looks like for the EGR Spacer? I'm referring to the one closest to the upper radiator hose (it's unlike the other four).
 

Bronco648

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Allen head cap bolt? Hmm, I don't think I have any of those in my pile of orphaned hardware. Metric, right?
 

AndyB.

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Yes, metric:


These are what the other four should look like.

 

Bronco648

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franklin2

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Resistor wire is measured in ohms per foot.

@19Walt93 knows the internal resistance for a duraspark coil. Seems to me everyone i checked over the years was right around 6 ohms.
6 is way too high. The Ford spec is 1.05 to 1.15 ohms.

Think of the ignition coil like a tank you are filling with electricity. When the module first grounds the coil and the coil starts filling up with energy, to the circuit and the module it looks like a dead short for a instant. The small resistance in the circuit throttles the amount of current that is able to pass through the circuit, and the module is part of this circuit. As the coil fills up, the amount of current is less and less.

That is why the module tends to fail without the resistor, there is too much current going through it. 1 ohm is not much resistance, but it is enough to drop the voltage across the coil from 12 down to 9-10v when the engine is running.

The Ford TFI and the GM HEI both have current limiting circuits built into the module, so they do not need external resistance.
 

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6 is way too high. The Ford spec is 1.05 to 1.15 ohms.

Think of the ignition coil like a tank you are filling with electricity. When the module first grounds the coil and the coil starts filling up with energy, to the circuit and the module it looks like a dead short for a instant. The small resistance in the circuit throttles the amount of current that is able to pass through the circuit, and the module is part of this circuit. As the coil fills up, the amount of current is less and less.

That is why the module tends to fail without the resistor, there is too much current going through it. 1 ohm is not much resistance, but it is enough to drop the voltage across the coil from 12 down to 9-10v when the engine is running.

The Ford TFI and the GM HEI both have current limiting circuits built into the module, so they do not need external resistance.
I wasn't speaking of the ballast. I was referring to the coil. The only Duraspark schematic i have is for a 2.0L in my 85 EVTM (you also posted it) and it says 1.33 ohms I believe. But the coil also has some internal resistance.ive used a ton of Bosch blue coil over the years. It was my coil of choice for VW pointed ignitions and the popular electronic ignition conversions. Those coils are internally resisted and they ohm out right about 6 ohms. They work fine in the instances I've used them. I'm 95% sure I used one in my V8 duraspark swaped Ranger... with no resistor wire or ballast.

I did look online and did see Ford Duraspark coils have 0.7 ohms internally. I swear Walt had made mention of them being higher then that.
 

franklin2

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Manuals are our friends.
So that manual says the ballast resistor can be .8 to 1.6 ohms and still be serviceable.

In a pinch people have used the resistors found on older Chrysler products with success, even though their values are a little different.
 

AndyB.

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Also, I don’t know how this could fit into a duraspark 2 harness, but the only ballast resistor listed for any 1985 light truck applications is d7az-12250-a.
 

19Walt93

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Resistor wire is measured in ohms per foot.

@19Walt93 knows the internal resistance for a duraspark coil. Seems to me everyone i checked over the years was right around 6 ohms.
Nope, if I remember right it's 1.1 to 1.3 ohms. Lower resistance will make a little hotter spark but your module will die early and often.
 

Bronco648

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2WD
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14"
Nope, if I remember right it's 1.1 to 1.3 ohms. Lower resistance will make a little hotter spark but your module will die early and often.
So, @ 1.4 Ohms am I OK with the NAPA coil or should I go with the Accel coil and in-line resistor (kinda lost now)?
 

Bronco648

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Tire Size
14"
Also, the EGR spacer & 2150 are mounted but this doesn't seem right:

20220813_105758.jpg


  1. The kick down tube pulls the kick down lever so far back that there's no way that adjusting screw can do anything.
  2. The ball on the end of the post seems too small for the socket.
  3. The socket is too far forward to snap onto the ball.
(yes, I know the carb nuts are not tightened down)
 

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